1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/gcTimer.hpp"
41 #include "gc_implementation/shared/gcTrace.hpp"
42 #include "gc_implementation/shared/gcTraceTime.hpp"
43 #include "gc_implementation/shared/isGCActiveMark.hpp"
44 #include "gc_interface/collectedHeap.inline.hpp"
45 #include "memory/allocation.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
66
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
68
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
73
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy suspicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential interference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
131
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
142
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
151
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
168
169
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
210
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
218
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
228
229 _gc_stats = new CMSGCStats();
230
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the minimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
271
272
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _initiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
298
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
303
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
317
318 }
319 }
320
321 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
326 gch->gen_policy()->size_policy();
327 assert(sp->is_gc_cms_adaptive_size_policy(),
328 "Wrong type of size policy");
329 return sp;
330 }
331
332 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
333 CMSGCAdaptivePolicyCounters* results =
334 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
335 assert(
336 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
337 "Wrong gc policy counter kind");
338 return results;
339 }
340
341
342 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
343
344 const char* gen_name = "old";
345
346 // Generation Counters - generation 1, 1 subspace
347 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
348
349 _space_counters = new GSpaceCounters(gen_name, 0,
350 _virtual_space.reserved_size(),
351 this, _gen_counters);
352 }
353
354 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
355 _cms_gen(cms_gen)
356 {
357 assert(alpha <= 100, "bad value");
358 _saved_alpha = alpha;
359
360 // Initialize the alphas to the bootstrap value of 100.
361 _gc0_alpha = _cms_alpha = 100;
362
363 _cms_begin_time.update();
364 _cms_end_time.update();
365
366 _gc0_duration = 0.0;
367 _gc0_period = 0.0;
368 _gc0_promoted = 0;
369
370 _cms_duration = 0.0;
371 _cms_period = 0.0;
372 _cms_allocated = 0;
373
374 _cms_used_at_gc0_begin = 0;
375 _cms_used_at_gc0_end = 0;
376 _allow_duty_cycle_reduction = false;
377 _valid_bits = 0;
378 _icms_duty_cycle = CMSIncrementalDutyCycle;
379 }
380
381 double CMSStats::cms_free_adjustment_factor(size_t free) const {
382 // TBD: CR 6909490
383 return 1.0;
384 }
385
386 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
387 }
388
389 // If promotion failure handling is on use
390 // the padded average size of the promotion for each
391 // young generation collection.
392 double CMSStats::time_until_cms_gen_full() const {
393 size_t cms_free = _cms_gen->cmsSpace()->free();
394 GenCollectedHeap* gch = GenCollectedHeap::heap();
395 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
396 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
397 if (cms_free > expected_promotion) {
398 // Start a cms collection if there isn't enough space to promote
399 // for the next minor collection. Use the padded average as
400 // a safety factor.
401 cms_free -= expected_promotion;
402
403 // Adjust by the safety factor.
404 double cms_free_dbl = (double)cms_free;
405 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
406 // Apply a further correction factor which tries to adjust
407 // for recent occurance of concurrent mode failures.
408 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
409 cms_free_dbl = cms_free_dbl * cms_adjustment;
410
411 if (PrintGCDetails && Verbose) {
412 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
413 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
414 cms_free, expected_promotion);
415 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
416 cms_free_dbl, cms_consumption_rate() + 1.0);
417 }
418 // Add 1 in case the consumption rate goes to zero.
419 return cms_free_dbl / (cms_consumption_rate() + 1.0);
420 }
421 return 0.0;
422 }
423
424 // Compare the duration of the cms collection to the
425 // time remaining before the cms generation is empty.
426 // Note that the time from the start of the cms collection
427 // to the start of the cms sweep (less than the total
428 // duration of the cms collection) can be used. This
429 // has been tried and some applications experienced
430 // promotion failures early in execution. This was
431 // possibly because the averages were not accurate
432 // enough at the beginning.
433 double CMSStats::time_until_cms_start() const {
434 // We add "gc0_period" to the "work" calculation
435 // below because this query is done (mostly) at the
436 // end of a scavenge, so we need to conservatively
437 // account for that much possible delay
438 // in the query so as to avoid concurrent mode failures
439 // due to starting the collection just a wee bit too
440 // late.
441 double work = cms_duration() + gc0_period();
442 double deadline = time_until_cms_gen_full();
443 // If a concurrent mode failure occurred recently, we want to be
444 // more conservative and halve our expected time_until_cms_gen_full()
445 if (work > deadline) {
446 if (Verbose && PrintGCDetails) {
447 gclog_or_tty->print(
448 " CMSCollector: collect because of anticipated promotion "
449 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
450 gc0_period(), time_until_cms_gen_full());
451 }
452 return 0.0;
453 }
454 return work - deadline;
455 }
456
457 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
458 // amount of change to prevent wild oscillation.
459 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
460 unsigned int new_duty_cycle) {
461 assert(old_duty_cycle <= 100, "bad input value");
462 assert(new_duty_cycle <= 100, "bad input value");
463
464 // Note: use subtraction with caution since it may underflow (values are
465 // unsigned). Addition is safe since we're in the range 0-100.
466 unsigned int damped_duty_cycle = new_duty_cycle;
467 if (new_duty_cycle < old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
469 if (new_duty_cycle + largest_delta < old_duty_cycle) {
470 damped_duty_cycle = old_duty_cycle - largest_delta;
471 }
472 } else if (new_duty_cycle > old_duty_cycle) {
473 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
474 if (new_duty_cycle > old_duty_cycle + largest_delta) {
475 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
476 }
477 }
478 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
479
480 if (CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
482 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
483 }
484 return damped_duty_cycle;
485 }
486
487 unsigned int CMSStats::icms_update_duty_cycle_impl() {
488 assert(CMSIncrementalPacing && valid(),
489 "should be handled in icms_update_duty_cycle()");
490
491 double cms_time_so_far = cms_timer().seconds();
492 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
493 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
494
495 // Avoid division by 0.
496 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
497 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
498
499 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
500 if (new_duty_cycle > _icms_duty_cycle) {
501 // Avoid very small duty cycles (1 or 2); 0 is allowed.
502 if (new_duty_cycle > 2) {
503 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
504 new_duty_cycle);
505 }
506 } else if (_allow_duty_cycle_reduction) {
507 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
508 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
509 // Respect the minimum duty cycle.
510 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
511 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
512 }
513
514 if (PrintGCDetails || CMSTraceIncrementalPacing) {
515 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
516 }
517
518 _allow_duty_cycle_reduction = false;
519 return _icms_duty_cycle;
520 }
521
522 #ifndef PRODUCT
523 void CMSStats::print_on(outputStream *st) const {
524 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
525 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
526 gc0_duration(), gc0_period(), gc0_promoted());
527 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
528 cms_duration(), cms_duration_per_mb(),
529 cms_period(), cms_allocated());
530 st->print(",cms_since_beg=%g,cms_since_end=%g",
531 cms_time_since_begin(), cms_time_since_end());
532 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
533 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
534 if (CMSIncrementalMode) {
535 st->print(",dc=%d", icms_duty_cycle());
536 }
537
538 if (valid()) {
539 st->print(",promo_rate=%g,cms_alloc_rate=%g",
540 promotion_rate(), cms_allocation_rate());
541 st->print(",cms_consumption_rate=%g,time_until_full=%g",
542 cms_consumption_rate(), time_until_cms_gen_full());
543 }
544 st->print(" ");
545 }
546 #endif // #ifndef PRODUCT
547
548 CMSCollector::CollectorState CMSCollector::_collectorState =
549 CMSCollector::Idling;
550 bool CMSCollector::_foregroundGCIsActive = false;
551 bool CMSCollector::_foregroundGCShouldWait = false;
552
553 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
554 CardTableRS* ct,
555 ConcurrentMarkSweepPolicy* cp):
556 _cmsGen(cmsGen),
557 _ct(ct),
558 _ref_processor(NULL), // will be set later
559 _conc_workers(NULL), // may be set later
560 _abort_preclean(false),
561 _start_sampling(false),
562 _between_prologue_and_epilogue(false),
563 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
564 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
565 -1 /* lock-free */, "No_lock" /* dummy */),
566 _modUnionClosure(&_modUnionTable),
567 _modUnionClosurePar(&_modUnionTable),
568 // Adjust my span to cover old (cms) gen
569 _span(cmsGen->reserved()),
570 // Construct the is_alive_closure with _span & markBitMap
571 _is_alive_closure(_span, &_markBitMap),
572 _restart_addr(NULL),
573 _overflow_list(NULL),
574 _stats(cmsGen),
575 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
576 _eden_chunk_array(NULL), // may be set in ctor body
577 _eden_chunk_capacity(0), // -- ditto --
578 _eden_chunk_index(0), // -- ditto --
579 _survivor_plab_array(NULL), // -- ditto --
580 _survivor_chunk_array(NULL), // -- ditto --
581 _survivor_chunk_capacity(0), // -- ditto --
582 _survivor_chunk_index(0), // -- ditto --
583 _ser_pmc_preclean_ovflw(0),
584 _ser_kac_preclean_ovflw(0),
585 _ser_pmc_remark_ovflw(0),
586 _par_pmc_remark_ovflw(0),
587 _ser_kac_ovflw(0),
588 _par_kac_ovflw(0),
589 #ifndef PRODUCT
590 _num_par_pushes(0),
591 #endif
592 _collection_count_start(0),
593 _verifying(false),
594 _icms_start_limit(NULL),
595 _icms_stop_limit(NULL),
596 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
597 _completed_initialization(false),
598 _collector_policy(cp),
599 _should_unload_classes(CMSClassUnloadingEnabled),
600 _concurrent_cycles_since_last_unload(0),
601 _roots_scanning_options(SharedHeap::SO_None),
602 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
603 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
604 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
605 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
606 _cms_start_registered(false)
607 {
608 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
609 ExplicitGCInvokesConcurrent = true;
610 }
611 // Now expand the span and allocate the collection support structures
612 // (MUT, marking bit map etc.) to cover both generations subject to
613 // collection.
614
615 // For use by dirty card to oop closures.
616 _cmsGen->cmsSpace()->set_collector(this);
617
618 // Allocate MUT and marking bit map
619 {
620 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
621 if (!_markBitMap.allocate(_span)) {
622 warning("Failed to allocate CMS Bit Map");
623 return;
624 }
625 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
626 }
627 {
628 _modUnionTable.allocate(_span);
629 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
630 }
631
632 if (!_markStack.allocate(MarkStackSize)) {
633 warning("Failed to allocate CMS Marking Stack");
634 return;
635 }
636
637 // Support for multi-threaded concurrent phases
638 if (CMSConcurrentMTEnabled) {
639 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
640 // just for now
641 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
642 }
643 if (ConcGCThreads > 1) {
644 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
645 ConcGCThreads, true);
646 if (_conc_workers == NULL) {
647 warning("GC/CMS: _conc_workers allocation failure: "
648 "forcing -CMSConcurrentMTEnabled");
649 CMSConcurrentMTEnabled = false;
650 } else {
651 _conc_workers->initialize_workers();
652 }
653 } else {
654 CMSConcurrentMTEnabled = false;
655 }
656 }
657 if (!CMSConcurrentMTEnabled) {
658 ConcGCThreads = 0;
659 } else {
660 // Turn off CMSCleanOnEnter optimization temporarily for
661 // the MT case where it's not fixed yet; see 6178663.
662 CMSCleanOnEnter = false;
663 }
664 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
665 "Inconsistency");
666
667 // Parallel task queues; these are shared for the
668 // concurrent and stop-world phases of CMS, but
669 // are not shared with parallel scavenge (ParNew).
670 {
671 uint i;
672 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
673
674 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
675 || ParallelRefProcEnabled)
676 && num_queues > 0) {
677 _task_queues = new OopTaskQueueSet(num_queues);
678 if (_task_queues == NULL) {
679 warning("task_queues allocation failure.");
680 return;
681 }
682 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
683 if (_hash_seed == NULL) {
684 warning("_hash_seed array allocation failure");
685 return;
686 }
687
688 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
689 for (i = 0; i < num_queues; i++) {
690 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
691 if (q == NULL) {
692 warning("work_queue allocation failure.");
693 return;
694 }
695 _task_queues->register_queue(i, q);
696 }
697 for (i = 0; i < num_queues; i++) {
698 _task_queues->queue(i)->initialize();
699 _hash_seed[i] = 17; // copied from ParNew
700 }
701 }
702 }
703
704 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
705
706 // Clip CMSBootstrapOccupancy between 0 and 100.
707 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
708
709 _full_gcs_since_conc_gc = 0;
710
711 // Now tell CMS generations the identity of their collector
712 ConcurrentMarkSweepGeneration::set_collector(this);
713
714 // Create & start a CMS thread for this CMS collector
715 _cmsThread = ConcurrentMarkSweepThread::start(this);
716 assert(cmsThread() != NULL, "CMS Thread should have been created");
717 assert(cmsThread()->collector() == this,
718 "CMS Thread should refer to this gen");
719 assert(CGC_lock != NULL, "Where's the CGC_lock?");
720
721 // Support for parallelizing young gen rescan
722 GenCollectedHeap* gch = GenCollectedHeap::heap();
723 _young_gen = gch->prev_gen(_cmsGen);
724 if (gch->supports_inline_contig_alloc()) {
725 _top_addr = gch->top_addr();
726 _end_addr = gch->end_addr();
727 assert(_young_gen != NULL, "no _young_gen");
728 _eden_chunk_index = 0;
729 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
730 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
731 if (_eden_chunk_array == NULL) {
732 _eden_chunk_capacity = 0;
733 warning("GC/CMS: _eden_chunk_array allocation failure");
734 }
735 }
736 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
737
738 // Support for parallelizing survivor space rescan
739 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
740 const size_t max_plab_samples =
741 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
742
743 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
744 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
745 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
746 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
747 || _cursor == NULL) {
748 warning("Failed to allocate survivor plab/chunk array");
749 if (_survivor_plab_array != NULL) {
750 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
751 _survivor_plab_array = NULL;
752 }
753 if (_survivor_chunk_array != NULL) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
755 _survivor_chunk_array = NULL;
756 }
757 if (_cursor != NULL) {
758 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
759 _cursor = NULL;
760 }
761 } else {
762 _survivor_chunk_capacity = 2*max_plab_samples;
763 for (uint i = 0; i < ParallelGCThreads; i++) {
764 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
765 if (vec == NULL) {
766 warning("Failed to allocate survivor plab array");
767 for (int j = i; j > 0; j--) {
768 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
769 }
770 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
771 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
772 _survivor_plab_array = NULL;
773 _survivor_chunk_array = NULL;
774 _survivor_chunk_capacity = 0;
775 break;
776 } else {
777 ChunkArray* cur =
778 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
779 max_plab_samples);
780 assert(cur->end() == 0, "Should be 0");
781 assert(cur->array() == vec, "Should be vec");
782 assert(cur->capacity() == max_plab_samples, "Error");
783 }
784 }
785 }
786 }
787 assert( ( _survivor_plab_array != NULL
788 && _survivor_chunk_array != NULL)
789 || ( _survivor_chunk_capacity == 0
790 && _survivor_chunk_index == 0),
791 "Error");
792
793 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
794 _gc_counters = new CollectorCounters("CMS", 1);
795 _completed_initialization = true;
796 _inter_sweep_timer.start(); // start of time
797 }
798
799 const char* ConcurrentMarkSweepGeneration::name() const {
800 return "concurrent mark-sweep generation";
801 }
802 void ConcurrentMarkSweepGeneration::update_counters() {
803 if (UsePerfData) {
804 _space_counters->update_all();
805 _gen_counters->update_all();
806 }
807 }
808
809 // this is an optimized version of update_counters(). it takes the
810 // used value as a parameter rather than computing it.
811 //
812 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
813 if (UsePerfData) {
814 _space_counters->update_used(used);
815 _space_counters->update_capacity();
816 _gen_counters->update_all();
817 }
818 }
819
820 void ConcurrentMarkSweepGeneration::print() const {
821 Generation::print();
822 cmsSpace()->print();
823 }
824
825 #ifndef PRODUCT
826 void ConcurrentMarkSweepGeneration::print_statistics() {
827 cmsSpace()->printFLCensus(0);
828 }
829 #endif
830
831 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
832 GenCollectedHeap* gch = GenCollectedHeap::heap();
833 if (PrintGCDetails) {
834 if (Verbose) {
835 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
836 level(), short_name(), s, used(), capacity());
837 } else {
838 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
839 level(), short_name(), s, used() / K, capacity() / K);
840 }
841 }
842 if (Verbose) {
843 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
844 gch->used(), gch->capacity());
845 } else {
846 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
847 gch->used() / K, gch->capacity() / K);
848 }
849 }
850
851 size_t
852 ConcurrentMarkSweepGeneration::contiguous_available() const {
853 // dld proposes an improvement in precision here. If the committed
854 // part of the space ends in a free block we should add that to
855 // uncommitted size in the calculation below. Will make this
856 // change later, staying with the approximation below for the
857 // time being. -- ysr.
858 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
859 }
860
861 size_t
862 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
863 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
864 }
865
866 size_t ConcurrentMarkSweepGeneration::max_available() const {
867 return free() + _virtual_space.uncommitted_size();
868 }
869
870 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
871 size_t available = max_available();
872 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
873 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
874 if (Verbose && PrintGCDetails) {
875 gclog_or_tty->print_cr(
876 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
877 "max_promo("SIZE_FORMAT")",
878 res? "":" not", available, res? ">=":"<",
879 av_promo, max_promotion_in_bytes);
880 }
881 return res;
882 }
883
884 // At a promotion failure dump information on block layout in heap
885 // (cms old generation).
886 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
887 if (CMSDumpAtPromotionFailure) {
888 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
889 }
890 }
891
892 CompactibleSpace*
893 ConcurrentMarkSweepGeneration::first_compaction_space() const {
894 return _cmsSpace;
895 }
896
897 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
898 // Clear the promotion information. These pointers can be adjusted
899 // along with all the other pointers into the heap but
900 // compaction is expected to be a rare event with
901 // a heap using cms so don't do it without seeing the need.
902 if (CollectedHeap::use_parallel_gc_threads()) {
903 for (uint i = 0; i < ParallelGCThreads; i++) {
904 _par_gc_thread_states[i]->promo.reset();
905 }
906 }
907 }
908
909 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
910 blk->do_space(_cmsSpace);
911 }
912
913 void ConcurrentMarkSweepGeneration::compute_new_size() {
914 assert_locked_or_safepoint(Heap_lock);
915
916 // If incremental collection failed, we just want to expand
917 // to the limit.
918 if (incremental_collection_failed()) {
919 clear_incremental_collection_failed();
920 grow_to_reserved();
921 return;
922 }
923
924 // The heap has been compacted but not reset yet.
925 // Any metric such as free() or used() will be incorrect.
926
927 CardGeneration::compute_new_size();
928
929 // Reset again after a possible resizing
930 if (did_compact()) {
931 cmsSpace()->reset_after_compaction();
932 }
933 }
934
935 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
936 assert_locked_or_safepoint(Heap_lock);
937
938 // If incremental collection failed, we just want to expand
939 // to the limit.
940 if (incremental_collection_failed()) {
941 clear_incremental_collection_failed();
942 grow_to_reserved();
943 return;
944 }
945
946 double free_percentage = ((double) free()) / capacity();
947 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
948 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
949
950 // compute expansion delta needed for reaching desired free percentage
951 if (free_percentage < desired_free_percentage) {
952 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
953 assert(desired_capacity >= capacity(), "invalid expansion size");
954 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
955 if (PrintGCDetails && Verbose) {
956 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
957 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
958 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
959 gclog_or_tty->print_cr(" Desired free fraction %f",
960 desired_free_percentage);
961 gclog_or_tty->print_cr(" Maximum free fraction %f",
962 maximum_free_percentage);
963 gclog_or_tty->print_cr(" Capacity "SIZE_FORMAT, capacity()/1000);
964 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
965 desired_capacity/1000);
966 int prev_level = level() - 1;
967 if (prev_level >= 0) {
968 size_t prev_size = 0;
969 GenCollectedHeap* gch = GenCollectedHeap::heap();
970 Generation* prev_gen = gch->_gens[prev_level];
971 prev_size = prev_gen->capacity();
972 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
973 prev_size/1000);
974 }
975 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
976 unsafe_max_alloc_nogc()/1000);
977 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
978 contiguous_available()/1000);
979 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
980 expand_bytes);
981 }
982 // safe if expansion fails
983 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
984 if (PrintGCDetails && Verbose) {
985 gclog_or_tty->print_cr(" Expanded free fraction %f",
986 ((double) free()) / capacity());
987 }
988 } else {
989 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
990 assert(desired_capacity <= capacity(), "invalid expansion size");
991 size_t shrink_bytes = capacity() - desired_capacity;
992 // Don't shrink unless the delta is greater than the minimum shrink we want
993 if (shrink_bytes >= MinHeapDeltaBytes) {
994 shrink_free_list_by(shrink_bytes);
995 }
996 }
997 }
998
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1002
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1010
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1040
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 //
1058 // Can the P-bits be deleted now? JJJ
1059 //
1060 // 1. need to mark the object as live so it isn't collected
1061 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1062 // 3. need to mark the end of the object so marking, precleaning or sweeping
1063 // can skip over uninitialized or unparsable objects. An allocated
1064 // object is considered uninitialized for our purposes as long as
1065 // its klass word is NULL. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1075
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1101
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1132
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1138
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* young = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = young->as_DefNewGeneration()->eden();
1143
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1148
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1157
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1160
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1178
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1181
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1195
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 p2i(top), p2i(_icms_stop_limit),
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1222
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 p2i(top), p2i(space->end()),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1237
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1251
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1260
1261 return NULL;
1262 }
1263
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1269
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1275
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1304
1305
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1313
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 //
1328 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1329 //
1330 // STATE IDENTIFICATION: (64 bit+COOPS)
1331 // ------------------------------------
1332 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1333 //
1334 // OBJECT: klass_word installed; klass_word != 0;
1335 // obj->size() computes correct size
1336 //
1337 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1338 //
1339 //
1340 // STATE TRANSITION DIAGRAM
1341 //
1342 // mut / parnew mut / parnew
1343 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1344 // ^ |
1345 // |------------------------ DEAD <------------------------------------|
1346 // sweep mut
1347 //
1348 // While a block is in TRANSIENT state its size cannot be determined
1349 // so readers will either need to come back later or stall until
1350 // the size can be determined. Note that for the case of direct
1351 // allocation, P-bits, when available, may be used to determine the
1352 // size of an object that may not yet have been initialized.
1353
1354 // Things to support parallel young-gen collection.
1355 oop
1356 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1357 oop old, markOop m,
1358 size_t word_sz) {
1359 #ifndef PRODUCT
1360 if (Universe::heap()->promotion_should_fail()) {
1361 return NULL;
1362 }
1363 #endif // #ifndef PRODUCT
1364
1365 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1366 PromotionInfo* promoInfo = &ps->promo;
1367 // if we are tracking promotions, then first ensure space for
1368 // promotion (including spooling space for saving header if necessary).
1369 // then allocate and copy, then track promoted info if needed.
1370 // When tracking (see PromotionInfo::track()), the mark word may
1371 // be displaced and in this case restoration of the mark word
1372 // occurs in the (oop_since_save_marks_)iterate phase.
1373 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1374 // Out of space for allocating spooling buffers;
1375 // try expanding and allocating spooling buffers.
1376 if (!expand_and_ensure_spooling_space(promoInfo)) {
1377 return NULL;
1378 }
1379 }
1380 assert(promoInfo->has_spooling_space(), "Control point invariant");
1381 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1382 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1383 if (obj_ptr == NULL) {
1384 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1385 if (obj_ptr == NULL) {
1386 return NULL;
1387 }
1388 }
1389 oop obj = oop(obj_ptr);
1390 OrderAccess::storestore();
1391 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1392 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1393 // IMPORTANT: See note on object initialization for CMS above.
1394 // Otherwise, copy the object. Here we must be careful to insert the
1395 // klass pointer last, since this marks the block as an allocated object.
1396 // Except with compressed oops it's the mark word.
1397 HeapWord* old_ptr = (HeapWord*)old;
1398 // Restore the mark word copied above.
1399 obj->set_mark(m);
1400 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1401 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1402 OrderAccess::storestore();
1403
1404 if (UseCompressedClassPointers) {
1405 // Copy gap missed by (aligned) header size calculation below
1406 obj->set_klass_gap(old->klass_gap());
1407 }
1408 if (word_sz > (size_t)oopDesc::header_size()) {
1409 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1410 obj_ptr + oopDesc::header_size(),
1411 word_sz - oopDesc::header_size());
1412 }
1413
1414 // Now we can track the promoted object, if necessary. We take care
1415 // to delay the transition from uninitialized to full object
1416 // (i.e., insertion of klass pointer) until after, so that it
1417 // atomically becomes a promoted object.
1418 if (promoInfo->tracking()) {
1419 promoInfo->track((PromotedObject*)obj, old->klass());
1420 }
1421 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1422 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1423 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1424
1425 // Finally, install the klass pointer (this should be volatile).
1426 OrderAccess::storestore();
1427 obj->set_klass(old->klass());
1428 // We should now be able to calculate the right size for this object
1429 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1430
1431 collector()->promoted(true, // parallel
1432 obj_ptr, old->is_objArray(), word_sz);
1433
1434 NOT_PRODUCT(
1435 Atomic::inc_ptr(&_numObjectsPromoted);
1436 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1437 )
1438
1439 return obj;
1440 }
1441
1442 void
1443 ConcurrentMarkSweepGeneration::
1444 par_promote_alloc_undo(int thread_num,
1445 HeapWord* obj, size_t word_sz) {
1446 // CMS does not support promotion undo.
1447 ShouldNotReachHere();
1448 }
1449
1450 void
1451 ConcurrentMarkSweepGeneration::
1452 par_promote_alloc_done(int thread_num) {
1453 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1454 ps->lab.retire(thread_num);
1455 }
1456
1457 void
1458 ConcurrentMarkSweepGeneration::
1459 par_oop_since_save_marks_iterate_done(int thread_num) {
1460 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1461 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1462 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1463 }
1464
1465 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1466 size_t size,
1467 bool tlab)
1468 {
1469 // We allow a STW collection only if a full
1470 // collection was requested.
1471 return full || should_allocate(size, tlab); // FIX ME !!!
1472 // This and promotion failure handling are connected at the
1473 // hip and should be fixed by untying them.
1474 }
1475
1476 bool CMSCollector::shouldConcurrentCollect() {
1477 if (_full_gc_requested) {
1478 if (Verbose && PrintGCDetails) {
1479 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1480 " gc request (or gc_locker)");
1481 }
1482 return true;
1483 }
1484
1485 // For debugging purposes, change the type of collection.
1486 // If the rotation is not on the concurrent collection
1487 // type, don't start a concurrent collection.
1488 NOT_PRODUCT(
1489 if (RotateCMSCollectionTypes &&
1490 (_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1492 assert(_cmsGen->debug_collection_type() !=
1493 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1494 "Bad cms collection type");
1495 return false;
1496 }
1497 )
1498
1499 FreelistLocker x(this);
1500 // ------------------------------------------------------------------
1501 // Print out lots of information which affects the initiation of
1502 // a collection.
1503 if (PrintCMSInitiationStatistics && stats().valid()) {
1504 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1505 gclog_or_tty->stamp();
1506 gclog_or_tty->cr();
1507 stats().print_on(gclog_or_tty);
1508 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1509 stats().time_until_cms_gen_full());
1510 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1511 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1512 _cmsGen->contiguous_available());
1513 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1514 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1515 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1516 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1517 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1518 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1519 gclog_or_tty->print_cr("metadata initialized %d",
1520 MetaspaceGC::should_concurrent_collect());
1521 }
1522 // ------------------------------------------------------------------
1523
1524 // If the estimated time to complete a cms collection (cms_duration())
1525 // is less than the estimated time remaining until the cms generation
1526 // is full, start a collection.
1527 if (!UseCMSInitiatingOccupancyOnly) {
1528 if (stats().valid()) {
1529 if (stats().time_until_cms_start() == 0.0) {
1530 return true;
1531 }
1532 } else {
1533 // We want to conservatively collect somewhat early in order
1534 // to try and "bootstrap" our CMS/promotion statistics;
1535 // this branch will not fire after the first successful CMS
1536 // collection because the stats should then be valid.
1537 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1538 if (Verbose && PrintGCDetails) {
1539 gclog_or_tty->print_cr(
1540 " CMSCollector: collect for bootstrapping statistics:"
1541 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1542 _bootstrap_occupancy);
1543 }
1544 return true;
1545 }
1546 }
1547 }
1548
1549 // Otherwise, we start a collection cycle if
1550 // old gen want a collection cycle started. Each may use
1551 // an appropriate criterion for making this decision.
1552 // XXX We need to make sure that the gen expansion
1553 // criterion dovetails well with this. XXX NEED TO FIX THIS
1554 if (_cmsGen->should_concurrent_collect()) {
1555 if (Verbose && PrintGCDetails) {
1556 gclog_or_tty->print_cr("CMS old gen initiated");
1557 }
1558 return true;
1559 }
1560
1561 // We start a collection if we believe an incremental collection may fail;
1562 // this is not likely to be productive in practice because it's probably too
1563 // late anyway.
1564 GenCollectedHeap* gch = GenCollectedHeap::heap();
1565 assert(gch->collector_policy()->is_generation_policy(),
1566 "You may want to check the correctness of the following");
1567 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1568 if (Verbose && PrintGCDetails) {
1569 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1570 }
1571 return true;
1572 }
1573
1574 if (MetaspaceGC::should_concurrent_collect()) {
1575 if (Verbose && PrintGCDetails) {
1576 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1577 }
1578 return true;
1579 }
1580
1581 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1582 if (CMSTriggerInterval >= 0) {
1583 if (CMSTriggerInterval == 0) {
1584 // Trigger always
1585 return true;
1586 }
1587
1588 // Check the CMS time since begin (we do not check the stats validity
1589 // as we want to be able to trigger the first CMS cycle as well)
1590 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1591 if (Verbose && PrintGCDetails) {
1592 if (stats().valid()) {
1593 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1594 stats().cms_time_since_begin());
1595 } else {
1596 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1597 }
1598 }
1599 return true;
1600 }
1601 }
1602
1603 return false;
1604 }
1605
1606 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1607
1608 // Clear _expansion_cause fields of constituent generations
1609 void CMSCollector::clear_expansion_cause() {
1610 _cmsGen->clear_expansion_cause();
1611 }
1612
1613 // We should be conservative in starting a collection cycle. To
1614 // start too eagerly runs the risk of collecting too often in the
1615 // extreme. To collect too rarely falls back on full collections,
1616 // which works, even if not optimum in terms of concurrent work.
1617 // As a work around for too eagerly collecting, use the flag
1618 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1619 // giving the user an easily understandable way of controlling the
1620 // collections.
1621 // We want to start a new collection cycle if any of the following
1622 // conditions hold:
1623 // . our current occupancy exceeds the configured initiating occupancy
1624 // for this generation, or
1625 // . we recently needed to expand this space and have not, since that
1626 // expansion, done a collection of this generation, or
1627 // . the underlying space believes that it may be a good idea to initiate
1628 // a concurrent collection (this may be based on criteria such as the
1629 // following: the space uses linear allocation and linear allocation is
1630 // going to fail, or there is believed to be excessive fragmentation in
1631 // the generation, etc... or ...
1632 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1633 // the case of the old generation; see CR 6543076):
1634 // we may be approaching a point at which allocation requests may fail because
1635 // we will be out of sufficient free space given allocation rate estimates.]
1636 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1637
1638 assert_lock_strong(freelistLock());
1639 if (occupancy() > initiating_occupancy()) {
1640 if (PrintGCDetails && Verbose) {
1641 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1642 short_name(), occupancy(), initiating_occupancy());
1643 }
1644 return true;
1645 }
1646 if (UseCMSInitiatingOccupancyOnly) {
1647 return false;
1648 }
1649 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1650 if (PrintGCDetails && Verbose) {
1651 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1652 short_name());
1653 }
1654 return true;
1655 }
1656 if (_cmsSpace->should_concurrent_collect()) {
1657 if (PrintGCDetails && Verbose) {
1658 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1659 short_name());
1660 }
1661 return true;
1662 }
1663 return false;
1664 }
1665
1666 void ConcurrentMarkSweepGeneration::collect(bool full,
1667 bool clear_all_soft_refs,
1668 size_t size,
1669 bool tlab)
1670 {
1671 collector()->collect(full, clear_all_soft_refs, size, tlab);
1672 }
1673
1674 void CMSCollector::collect(bool full,
1675 bool clear_all_soft_refs,
1676 size_t size,
1677 bool tlab)
1678 {
1679 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1680 // For debugging purposes skip the collection if the state
1681 // is not currently idle
1682 if (TraceCMSState) {
1683 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1684 Thread::current(), full, _collectorState);
1685 }
1686 return;
1687 }
1688
1689 // The following "if" branch is present for defensive reasons.
1690 // In the current uses of this interface, it can be replaced with:
1691 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1692 // But I am not placing that assert here to allow future
1693 // generality in invoking this interface.
1694 if (GC_locker::is_active()) {
1695 // A consistency test for GC_locker
1696 assert(GC_locker::needs_gc(), "Should have been set already");
1697 // Skip this foreground collection, instead
1698 // expanding the heap if necessary.
1699 // Need the free list locks for the call to free() in compute_new_size()
1700 compute_new_size();
1701 return;
1702 }
1703 acquire_control_and_collect(full, clear_all_soft_refs);
1704 _full_gcs_since_conc_gc++;
1705 }
1706
1707 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1708 GenCollectedHeap* gch = GenCollectedHeap::heap();
1709 unsigned int gc_count = gch->total_full_collections();
1710 if (gc_count == full_gc_count) {
1711 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1712 _full_gc_requested = true;
1713 _full_gc_cause = cause;
1714 CGC_lock->notify(); // nudge CMS thread
1715 } else {
1716 assert(gc_count > full_gc_count, "Error: causal loop");
1717 }
1718 }
1719
1720 bool CMSCollector::is_external_interruption() {
1721 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1722 return GCCause::is_user_requested_gc(cause) ||
1723 GCCause::is_serviceability_requested_gc(cause);
1724 }
1725
1726 void CMSCollector::report_concurrent_mode_interruption() {
1727 if (is_external_interruption()) {
1728 if (PrintGCDetails) {
1729 gclog_or_tty->print(" (concurrent mode interrupted)");
1730 }
1731 } else {
1732 if (PrintGCDetails) {
1733 gclog_or_tty->print(" (concurrent mode failure)");
1734 }
1735 _gc_tracer_cm->report_concurrent_mode_failure();
1736 }
1737 }
1738
1739
1740 // The foreground and background collectors need to coordinate in order
1741 // to make sure that they do not mutually interfere with CMS collections.
1742 // When a background collection is active,
1743 // the foreground collector may need to take over (preempt) and
1744 // synchronously complete an ongoing collection. Depending on the
1745 // frequency of the background collections and the heap usage
1746 // of the application, this preemption can be seldom or frequent.
1747 // There are only certain
1748 // points in the background collection that the "collection-baton"
1749 // can be passed to the foreground collector.
1750 //
1751 // The foreground collector will wait for the baton before
1752 // starting any part of the collection. The foreground collector
1753 // will only wait at one location.
1754 //
1755 // The background collector will yield the baton before starting a new
1756 // phase of the collection (e.g., before initial marking, marking from roots,
1757 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1758 // of the loop which switches the phases. The background collector does some
1759 // of the phases (initial mark, final re-mark) with the world stopped.
1760 // Because of locking involved in stopping the world,
1761 // the foreground collector should not block waiting for the background
1762 // collector when it is doing a stop-the-world phase. The background
1763 // collector will yield the baton at an additional point just before
1764 // it enters a stop-the-world phase. Once the world is stopped, the
1765 // background collector checks the phase of the collection. If the
1766 // phase has not changed, it proceeds with the collection. If the
1767 // phase has changed, it skips that phase of the collection. See
1768 // the comments on the use of the Heap_lock in collect_in_background().
1769 //
1770 // Variable used in baton passing.
1771 // _foregroundGCIsActive - Set to true by the foreground collector when
1772 // it wants the baton. The foreground clears it when it has finished
1773 // the collection.
1774 // _foregroundGCShouldWait - Set to true by the background collector
1775 // when it is running. The foreground collector waits while
1776 // _foregroundGCShouldWait is true.
1777 // CGC_lock - monitor used to protect access to the above variables
1778 // and to notify the foreground and background collectors.
1779 // _collectorState - current state of the CMS collection.
1780 //
1781 // The foreground collector
1782 // acquires the CGC_lock
1783 // sets _foregroundGCIsActive
1784 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1785 // various locks acquired in preparation for the collection
1786 // are released so as not to block the background collector
1787 // that is in the midst of a collection
1788 // proceeds with the collection
1789 // clears _foregroundGCIsActive
1790 // returns
1791 //
1792 // The background collector in a loop iterating on the phases of the
1793 // collection
1794 // acquires the CGC_lock
1795 // sets _foregroundGCShouldWait
1796 // if _foregroundGCIsActive is set
1797 // clears _foregroundGCShouldWait, notifies _CGC_lock
1798 // waits on _CGC_lock for _foregroundGCIsActive to become false
1799 // and exits the loop.
1800 // otherwise
1801 // proceed with that phase of the collection
1802 // if the phase is a stop-the-world phase,
1803 // yield the baton once more just before enqueueing
1804 // the stop-world CMS operation (executed by the VM thread).
1805 // returns after all phases of the collection are done
1806 //
1807
1808 void CMSCollector::acquire_control_and_collect(bool full,
1809 bool clear_all_soft_refs) {
1810 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1811 assert(!Thread::current()->is_ConcurrentGC_thread(),
1812 "shouldn't try to acquire control from self!");
1813
1814 // Start the protocol for acquiring control of the
1815 // collection from the background collector (aka CMS thread).
1816 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1817 "VM thread should have CMS token");
1818 // Remember the possibly interrupted state of an ongoing
1819 // concurrent collection
1820 CollectorState first_state = _collectorState;
1821
1822 // Signal to a possibly ongoing concurrent collection that
1823 // we want to do a foreground collection.
1824 _foregroundGCIsActive = true;
1825
1826 // Disable incremental mode during a foreground collection.
1827 ICMSDisabler icms_disabler;
1828
1829 // release locks and wait for a notify from the background collector
1830 // releasing the locks in only necessary for phases which
1831 // do yields to improve the granularity of the collection.
1832 assert_lock_strong(bitMapLock());
1833 // We need to lock the Free list lock for the space that we are
1834 // currently collecting.
1835 assert(haveFreelistLocks(), "Must be holding free list locks");
1836 bitMapLock()->unlock();
1837 releaseFreelistLocks();
1838 {
1839 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1840 if (_foregroundGCShouldWait) {
1841 // We are going to be waiting for action for the CMS thread;
1842 // it had better not be gone (for instance at shutdown)!
1843 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1844 "CMS thread must be running");
1845 // Wait here until the background collector gives us the go-ahead
1846 ConcurrentMarkSweepThread::clear_CMS_flag(
1847 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1848 // Get a possibly blocked CMS thread going:
1849 // Note that we set _foregroundGCIsActive true above,
1850 // without protection of the CGC_lock.
1851 CGC_lock->notify();
1852 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1853 "Possible deadlock");
1854 while (_foregroundGCShouldWait) {
1855 // wait for notification
1856 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1857 // Possibility of delay/starvation here, since CMS token does
1858 // not know to give priority to VM thread? Actually, i think
1859 // there wouldn't be any delay/starvation, but the proof of
1860 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1861 }
1862 ConcurrentMarkSweepThread::set_CMS_flag(
1863 ConcurrentMarkSweepThread::CMS_vm_has_token);
1864 }
1865 }
1866 // The CMS_token is already held. Get back the other locks.
1867 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1868 "VM thread should have CMS token");
1869 getFreelistLocks();
1870 bitMapLock()->lock_without_safepoint_check();
1871 if (TraceCMSState) {
1872 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1873 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1874 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1875 }
1876
1877 // Check if we need to do a compaction, or if not, whether
1878 // we need to start the mark-sweep from scratch.
1879 bool should_compact = false;
1880 bool should_start_over = false;
1881 decide_foreground_collection_type(clear_all_soft_refs,
1882 &should_compact, &should_start_over);
1883
1884 NOT_PRODUCT(
1885 if (RotateCMSCollectionTypes) {
1886 if (_cmsGen->debug_collection_type() ==
1887 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1888 should_compact = true;
1889 } else if (_cmsGen->debug_collection_type() ==
1890 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1891 should_compact = false;
1892 }
1893 }
1894 )
1895
1896 if (first_state > Idling) {
1897 report_concurrent_mode_interruption();
1898 }
1899
1900 set_did_compact(should_compact);
1901 if (should_compact) {
1902 // If the collection is being acquired from the background
1903 // collector, there may be references on the discovered
1904 // references lists that have NULL referents (being those
1905 // that were concurrently cleared by a mutator) or
1906 // that are no longer active (having been enqueued concurrently
1907 // by the mutator).
1908 // Scrub the list of those references because Mark-Sweep-Compact
1909 // code assumes referents are not NULL and that all discovered
1910 // Reference objects are active.
1911 ref_processor()->clean_up_discovered_references();
1912
1913 if (first_state > Idling) {
1914 save_heap_summary();
1915 }
1916
1917 do_compaction_work(clear_all_soft_refs);
1918
1919 // Has the GC time limit been exceeded?
1920 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1921 size_t max_eden_size = young_gen->max_capacity() -
1922 young_gen->to()->capacity() -
1923 young_gen->from()->capacity();
1924 GenCollectedHeap* gch = GenCollectedHeap::heap();
1925 GCCause::Cause gc_cause = gch->gc_cause();
1926 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1927 young_gen->eden()->used(),
1928 _cmsGen->max_capacity(),
1929 max_eden_size,
1930 full,
1931 gc_cause,
1932 gch->collector_policy());
1933 } else {
1934 do_mark_sweep_work(clear_all_soft_refs, first_state,
1935 should_start_over);
1936 }
1937 // Reset the expansion cause, now that we just completed
1938 // a collection cycle.
1939 clear_expansion_cause();
1940 _foregroundGCIsActive = false;
1941 return;
1942 }
1943
1944 // Resize the tenured generation
1945 // after obtaining the free list locks for the
1946 // two generations.
1947 void CMSCollector::compute_new_size() {
1948 assert_locked_or_safepoint(Heap_lock);
1949 FreelistLocker z(this);
1950 MetaspaceGC::compute_new_size();
1951 _cmsGen->compute_new_size_free_list();
1952 }
1953
1954 // A work method used by foreground collection to determine
1955 // what type of collection (compacting or not, continuing or fresh)
1956 // it should do.
1957 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1958 // and CMSCompactWhenClearAllSoftRefs the default in the future
1959 // and do away with the flags after a suitable period.
1960 void CMSCollector::decide_foreground_collection_type(
1961 bool clear_all_soft_refs, bool* should_compact,
1962 bool* should_start_over) {
1963 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1964 // flag is set, and we have either requested a System.gc() or
1965 // the number of full gc's since the last concurrent cycle
1966 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1967 // or if an incremental collection has failed
1968 GenCollectedHeap* gch = GenCollectedHeap::heap();
1969 assert(gch->collector_policy()->is_generation_policy(),
1970 "You may want to check the correctness of the following");
1971 // Inform cms gen if this was due to partial collection failing.
1972 // The CMS gen may use this fact to determine its expansion policy.
1973 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1974 assert(!_cmsGen->incremental_collection_failed(),
1975 "Should have been noticed, reacted to and cleared");
1976 _cmsGen->set_incremental_collection_failed();
1977 }
1978 *should_compact =
1979 UseCMSCompactAtFullCollection &&
1980 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1981 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1982 gch->incremental_collection_will_fail(true /* consult_young */));
1983 *should_start_over = false;
1984 if (clear_all_soft_refs && !*should_compact) {
1985 // We are about to do a last ditch collection attempt
1986 // so it would normally make sense to do a compaction
1987 // to reclaim as much space as possible.
1988 if (CMSCompactWhenClearAllSoftRefs) {
1989 // Default: The rationale is that in this case either
1990 // we are past the final marking phase, in which case
1991 // we'd have to start over, or so little has been done
1992 // that there's little point in saving that work. Compaction
1993 // appears to be the sensible choice in either case.
1994 *should_compact = true;
1995 } else {
1996 // We have been asked to clear all soft refs, but not to
1997 // compact. Make sure that we aren't past the final checkpoint
1998 // phase, for that is where we process soft refs. If we are already
1999 // past that phase, we'll need to redo the refs discovery phase and
2000 // if necessary clear soft refs that weren't previously
2001 // cleared. We do so by remembering the phase in which
2002 // we came in, and if we are past the refs processing
2003 // phase, we'll choose to just redo the mark-sweep
2004 // collection from scratch.
2005 if (_collectorState > FinalMarking) {
2006 // We are past the refs processing phase;
2007 // start over and do a fresh synchronous CMS cycle
2008 _collectorState = Resetting; // skip to reset to start new cycle
2009 reset(false /* == !asynch */);
2010 *should_start_over = true;
2011 } // else we can continue a possibly ongoing current cycle
2012 }
2013 }
2014 }
2015
2016 // A work method used by the foreground collector to do
2017 // a mark-sweep-compact.
2018 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
2019 GenCollectedHeap* gch = GenCollectedHeap::heap();
2020
2021 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2022 gc_timer->register_gc_start();
2023
2024 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2025 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2026
2027 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2028 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2029 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2030 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2031 }
2032
2033 // Sample collection interval time and reset for collection pause.
2034 if (UseAdaptiveSizePolicy) {
2035 size_policy()->msc_collection_begin();
2036 }
2037
2038 // Temporarily widen the span of the weak reference processing to
2039 // the entire heap.
2040 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2041 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2042 // Temporarily, clear the "is_alive_non_header" field of the
2043 // reference processor.
2044 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2045 // Temporarily make reference _processing_ single threaded (non-MT).
2046 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2047 // Temporarily make refs discovery atomic
2048 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2049 // Temporarily make reference _discovery_ single threaded (non-MT)
2050 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2051
2052 ref_processor()->set_enqueuing_is_done(false);
2053 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2054 ref_processor()->setup_policy(clear_all_soft_refs);
2055 // If an asynchronous collection finishes, the _modUnionTable is
2056 // all clear. If we are assuming the collection from an asynchronous
2057 // collection, clear the _modUnionTable.
2058 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2059 "_modUnionTable should be clear if the baton was not passed");
2060 _modUnionTable.clear_all();
2061 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2062 "mod union for klasses should be clear if the baton was passed");
2063 _ct->klass_rem_set()->clear_mod_union();
2064
2065 // We must adjust the allocation statistics being maintained
2066 // in the free list space. We do so by reading and clearing
2067 // the sweep timer and updating the block flux rate estimates below.
2068 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2069 if (_inter_sweep_timer.is_active()) {
2070 _inter_sweep_timer.stop();
2071 // Note that we do not use this sample to update the _inter_sweep_estimate.
2072 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2073 _inter_sweep_estimate.padded_average(),
2074 _intra_sweep_estimate.padded_average());
2075 }
2076
2077 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2078 ref_processor(), clear_all_soft_refs);
2079 #ifdef ASSERT
2080 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2081 size_t free_size = cms_space->free();
2082 assert(free_size ==
2083 pointer_delta(cms_space->end(), cms_space->compaction_top())
2084 * HeapWordSize,
2085 "All the free space should be compacted into one chunk at top");
2086 assert(cms_space->dictionary()->total_chunk_size(
2087 debug_only(cms_space->freelistLock())) == 0 ||
2088 cms_space->totalSizeInIndexedFreeLists() == 0,
2089 "All the free space should be in a single chunk");
2090 size_t num = cms_space->totalCount();
2091 assert((free_size == 0 && num == 0) ||
2092 (free_size > 0 && (num == 1 || num == 2)),
2093 "There should be at most 2 free chunks after compaction");
2094 #endif // ASSERT
2095 _collectorState = Resetting;
2096 assert(_restart_addr == NULL,
2097 "Should have been NULL'd before baton was passed");
2098 reset(false /* == !asynch */);
2099 _cmsGen->reset_after_compaction();
2100 _concurrent_cycles_since_last_unload = 0;
2101
2102 // Clear any data recorded in the PLAB chunk arrays.
2103 if (_survivor_plab_array != NULL) {
2104 reset_survivor_plab_arrays();
2105 }
2106
2107 // Adjust the per-size allocation stats for the next epoch.
2108 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2109 // Restart the "inter sweep timer" for the next epoch.
2110 _inter_sweep_timer.reset();
2111 _inter_sweep_timer.start();
2112
2113 // Sample collection pause time and reset for collection interval.
2114 if (UseAdaptiveSizePolicy) {
2115 size_policy()->msc_collection_end(gch->gc_cause());
2116 }
2117
2118 gc_timer->register_gc_end();
2119
2120 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2121
2122 // For a mark-sweep-compact, compute_new_size() will be called
2123 // in the heap's do_collection() method.
2124 }
2125
2126 // A work method used by the foreground collector to do
2127 // a mark-sweep, after taking over from a possibly on-going
2128 // concurrent mark-sweep collection.
2129 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2130 CollectorState first_state, bool should_start_over) {
2131 if (PrintGC && Verbose) {
2132 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2133 "collector with count %d",
2134 _full_gcs_since_conc_gc);
2135 }
2136 switch (_collectorState) {
2137 case Idling:
2138 if (first_state == Idling || should_start_over) {
2139 // The background GC was not active, or should
2140 // restarted from scratch; start the cycle.
2141 _collectorState = InitialMarking;
2142 }
2143 // If first_state was not Idling, then a background GC
2144 // was in progress and has now finished. No need to do it
2145 // again. Leave the state as Idling.
2146 break;
2147 case Precleaning:
2148 // In the foreground case don't do the precleaning since
2149 // it is not done concurrently and there is extra work
2150 // required.
2151 _collectorState = FinalMarking;
2152 }
2153 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2154
2155 // For a mark-sweep, compute_new_size() will be called
2156 // in the heap's do_collection() method.
2157 }
2158
2159
2160 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2161 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2162 EdenSpace* eden_space = dng->eden();
2163 ContiguousSpace* from_space = dng->from();
2164 ContiguousSpace* to_space = dng->to();
2165 // Eden
2166 if (_eden_chunk_array != NULL) {
2167 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2168 eden_space->bottom(), eden_space->top(),
2169 eden_space->end(), eden_space->capacity());
2170 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2171 "_eden_chunk_capacity=" SIZE_FORMAT,
2172 _eden_chunk_index, _eden_chunk_capacity);
2173 for (size_t i = 0; i < _eden_chunk_index; i++) {
2174 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2175 i, _eden_chunk_array[i]);
2176 }
2177 }
2178 // Survivor
2179 if (_survivor_chunk_array != NULL) {
2180 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2181 from_space->bottom(), from_space->top(),
2182 from_space->end(), from_space->capacity());
2183 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2184 "_survivor_chunk_capacity=" SIZE_FORMAT,
2185 _survivor_chunk_index, _survivor_chunk_capacity);
2186 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2187 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2188 i, _survivor_chunk_array[i]);
2189 }
2190 }
2191 }
2192
2193 void CMSCollector::getFreelistLocks() const {
2194 // Get locks for all free lists in all generations that this
2195 // collector is responsible for
2196 _cmsGen->freelistLock()->lock_without_safepoint_check();
2197 }
2198
2199 void CMSCollector::releaseFreelistLocks() const {
2200 // Release locks for all free lists in all generations that this
2201 // collector is responsible for
2202 _cmsGen->freelistLock()->unlock();
2203 }
2204
2205 bool CMSCollector::haveFreelistLocks() const {
2206 // Check locks for all free lists in all generations that this
2207 // collector is responsible for
2208 assert_lock_strong(_cmsGen->freelistLock());
2209 PRODUCT_ONLY(ShouldNotReachHere());
2210 return true;
2211 }
2212
2213 // A utility class that is used by the CMS collector to
2214 // temporarily "release" the foreground collector from its
2215 // usual obligation to wait for the background collector to
2216 // complete an ongoing phase before proceeding.
2217 class ReleaseForegroundGC: public StackObj {
2218 private:
2219 CMSCollector* _c;
2220 public:
2221 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2222 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2223 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2224 // allow a potentially blocked foreground collector to proceed
2225 _c->_foregroundGCShouldWait = false;
2226 if (_c->_foregroundGCIsActive) {
2227 CGC_lock->notify();
2228 }
2229 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2230 "Possible deadlock");
2231 }
2232
2233 ~ReleaseForegroundGC() {
2234 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2235 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2236 _c->_foregroundGCShouldWait = true;
2237 }
2238 };
2239
2240 // There are separate collect_in_background and collect_in_foreground because of
2241 // the different locking requirements of the background collector and the
2242 // foreground collector. There was originally an attempt to share
2243 // one "collect" method between the background collector and the foreground
2244 // collector but the if-then-else required made it cleaner to have
2245 // separate methods.
2246 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2247 assert(Thread::current()->is_ConcurrentGC_thread(),
2248 "A CMS asynchronous collection is only allowed on a CMS thread.");
2249
2250 GenCollectedHeap* gch = GenCollectedHeap::heap();
2251 {
2252 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2253 MutexLockerEx hl(Heap_lock, safepoint_check);
2254 FreelistLocker fll(this);
2255 MutexLockerEx x(CGC_lock, safepoint_check);
2256 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2257 // The foreground collector is active or we're
2258 // not using asynchronous collections. Skip this
2259 // background collection.
2260 assert(!_foregroundGCShouldWait, "Should be clear");
2261 return;
2262 } else {
2263 assert(_collectorState == Idling, "Should be idling before start.");
2264 _collectorState = InitialMarking;
2265 register_gc_start(cause);
2266 // Reset the expansion cause, now that we are about to begin
2267 // a new cycle.
2268 clear_expansion_cause();
2269
2270 // Clear the MetaspaceGC flag since a concurrent collection
2271 // is starting but also clear it after the collection.
2272 MetaspaceGC::set_should_concurrent_collect(false);
2273 }
2274 // Decide if we want to enable class unloading as part of the
2275 // ensuing concurrent GC cycle.
2276 update_should_unload_classes();
2277 _full_gc_requested = false; // acks all outstanding full gc requests
2278 _full_gc_cause = GCCause::_no_gc;
2279 // Signal that we are about to start a collection
2280 gch->increment_total_full_collections(); // ... starting a collection cycle
2281 _collection_count_start = gch->total_full_collections();
2282 }
2283
2284 // Used for PrintGC
2285 size_t prev_used;
2286 if (PrintGC && Verbose) {
2287 prev_used = _cmsGen->used(); // XXXPERM
2288 }
2289
2290 // The change of the collection state is normally done at this level;
2291 // the exceptions are phases that are executed while the world is
2292 // stopped. For those phases the change of state is done while the
2293 // world is stopped. For baton passing purposes this allows the
2294 // background collector to finish the phase and change state atomically.
2295 // The foreground collector cannot wait on a phase that is done
2296 // while the world is stopped because the foreground collector already
2297 // has the world stopped and would deadlock.
2298 while (_collectorState != Idling) {
2299 if (TraceCMSState) {
2300 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2301 Thread::current(), _collectorState);
2302 }
2303 // The foreground collector
2304 // holds the Heap_lock throughout its collection.
2305 // holds the CMS token (but not the lock)
2306 // except while it is waiting for the background collector to yield.
2307 //
2308 // The foreground collector should be blocked (not for long)
2309 // if the background collector is about to start a phase
2310 // executed with world stopped. If the background
2311 // collector has already started such a phase, the
2312 // foreground collector is blocked waiting for the
2313 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2314 // are executed in the VM thread.
2315 //
2316 // The locking order is
2317 // PendingListLock (PLL) -- if applicable (FinalMarking)
2318 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2319 // CMS token (claimed in
2320 // stop_world_and_do() -->
2321 // safepoint_synchronize() -->
2322 // CMSThread::synchronize())
2323
2324 {
2325 // Check if the FG collector wants us to yield.
2326 CMSTokenSync x(true); // is cms thread
2327 if (waitForForegroundGC()) {
2328 // We yielded to a foreground GC, nothing more to be
2329 // done this round.
2330 assert(_foregroundGCShouldWait == false, "We set it to false in "
2331 "waitForForegroundGC()");
2332 if (TraceCMSState) {
2333 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2334 " exiting collection CMS state %d",
2335 Thread::current(), _collectorState);
2336 }
2337 return;
2338 } else {
2339 // The background collector can run but check to see if the
2340 // foreground collector has done a collection while the
2341 // background collector was waiting to get the CGC_lock
2342 // above. If yes, break so that _foregroundGCShouldWait
2343 // is cleared before returning.
2344 if (_collectorState == Idling) {
2345 break;
2346 }
2347 }
2348 }
2349
2350 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2351 "should be waiting");
2352
2353 switch (_collectorState) {
2354 case InitialMarking:
2355 {
2356 ReleaseForegroundGC x(this);
2357 stats().record_cms_begin();
2358 VM_CMS_Initial_Mark initial_mark_op(this);
2359 VMThread::execute(&initial_mark_op);
2360 }
2361 // The collector state may be any legal state at this point
2362 // since the background collector may have yielded to the
2363 // foreground collector.
2364 break;
2365 case Marking:
2366 // initial marking in checkpointRootsInitialWork has been completed
2367 if (markFromRoots(true)) { // we were successful
2368 assert(_collectorState == Precleaning, "Collector state should "
2369 "have changed");
2370 } else {
2371 assert(_foregroundGCIsActive, "Internal state inconsistency");
2372 }
2373 break;
2374 case Precleaning:
2375 if (UseAdaptiveSizePolicy) {
2376 size_policy()->concurrent_precleaning_begin();
2377 }
2378 // marking from roots in markFromRoots has been completed
2379 preclean();
2380 if (UseAdaptiveSizePolicy) {
2381 size_policy()->concurrent_precleaning_end();
2382 }
2383 assert(_collectorState == AbortablePreclean ||
2384 _collectorState == FinalMarking,
2385 "Collector state should have changed");
2386 break;
2387 case AbortablePreclean:
2388 if (UseAdaptiveSizePolicy) {
2389 size_policy()->concurrent_phases_resume();
2390 }
2391 abortable_preclean();
2392 if (UseAdaptiveSizePolicy) {
2393 size_policy()->concurrent_precleaning_end();
2394 }
2395 assert(_collectorState == FinalMarking, "Collector state should "
2396 "have changed");
2397 break;
2398 case FinalMarking:
2399 {
2400 ReleaseForegroundGC x(this);
2401
2402 VM_CMS_Final_Remark final_remark_op(this);
2403 VMThread::execute(&final_remark_op);
2404 }
2405 assert(_foregroundGCShouldWait, "block post-condition");
2406 break;
2407 case Sweeping:
2408 if (UseAdaptiveSizePolicy) {
2409 size_policy()->concurrent_sweeping_begin();
2410 }
2411 // final marking in checkpointRootsFinal has been completed
2412 sweep(true);
2413 assert(_collectorState == Resizing, "Collector state change "
2414 "to Resizing must be done under the free_list_lock");
2415 _full_gcs_since_conc_gc = 0;
2416
2417 // Stop the timers for adaptive size policy for the concurrent phases
2418 if (UseAdaptiveSizePolicy) {
2419 size_policy()->concurrent_sweeping_end();
2420 size_policy()->concurrent_phases_end(gch->gc_cause(),
2421 gch->prev_gen(_cmsGen)->capacity(),
2422 _cmsGen->free());
2423 }
2424
2425 case Resizing: {
2426 // Sweeping has been completed...
2427 // At this point the background collection has completed.
2428 // Don't move the call to compute_new_size() down
2429 // into code that might be executed if the background
2430 // collection was preempted.
2431 {
2432 ReleaseForegroundGC x(this); // unblock FG collection
2433 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2434 CMSTokenSync z(true); // not strictly needed.
2435 if (_collectorState == Resizing) {
2436 compute_new_size();
2437 save_heap_summary();
2438 _collectorState = Resetting;
2439 } else {
2440 assert(_collectorState == Idling, "The state should only change"
2441 " because the foreground collector has finished the collection");
2442 }
2443 }
2444 break;
2445 }
2446 case Resetting:
2447 // CMS heap resizing has been completed
2448 reset(true);
2449 assert(_collectorState == Idling, "Collector state should "
2450 "have changed");
2451
2452 MetaspaceGC::set_should_concurrent_collect(false);
2453
2454 stats().record_cms_end();
2455 // Don't move the concurrent_phases_end() and compute_new_size()
2456 // calls to here because a preempted background collection
2457 // has it's state set to "Resetting".
2458 break;
2459 case Idling:
2460 default:
2461 ShouldNotReachHere();
2462 break;
2463 }
2464 if (TraceCMSState) {
2465 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2466 Thread::current(), _collectorState);
2467 }
2468 assert(_foregroundGCShouldWait, "block post-condition");
2469 }
2470
2471 // Should this be in gc_epilogue?
2472 collector_policy()->counters()->update_counters();
2473
2474 {
2475 // Clear _foregroundGCShouldWait and, in the event that the
2476 // foreground collector is waiting, notify it, before
2477 // returning.
2478 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2479 _foregroundGCShouldWait = false;
2480 if (_foregroundGCIsActive) {
2481 CGC_lock->notify();
2482 }
2483 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2484 "Possible deadlock");
2485 }
2486 if (TraceCMSState) {
2487 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2488 " exiting collection CMS state %d",
2489 Thread::current(), _collectorState);
2490 }
2491 if (PrintGC && Verbose) {
2492 _cmsGen->print_heap_change(prev_used);
2493 }
2494 }
2495
2496 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2497 if (!_cms_start_registered) {
2498 register_gc_start(cause);
2499 }
2500 }
2501
2502 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2503 _cms_start_registered = true;
2504 _gc_timer_cm->register_gc_start();
2505 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2506 }
2507
2508 void CMSCollector::register_gc_end() {
2509 if (_cms_start_registered) {
2510 report_heap_summary(GCWhen::AfterGC);
2511
2512 _gc_timer_cm->register_gc_end();
2513 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2514 _cms_start_registered = false;
2515 }
2516 }
2517
2518 void CMSCollector::save_heap_summary() {
2519 GenCollectedHeap* gch = GenCollectedHeap::heap();
2520 _last_heap_summary = gch->create_heap_summary();
2521 _last_metaspace_summary = gch->create_metaspace_summary();
2522 }
2523
2524 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2525 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2526 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2527 }
2528
2529 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2530 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2531 "Foreground collector should be waiting, not executing");
2532 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2533 "may only be done by the VM Thread with the world stopped");
2534 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2535 "VM thread should have CMS token");
2536
2537 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2538 true, NULL);)
2539 if (UseAdaptiveSizePolicy) {
2540 size_policy()->ms_collection_begin();
2541 }
2542 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2543
2544 HandleMark hm; // Discard invalid handles created during verification
2545
2546 if (VerifyBeforeGC &&
2547 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2548 Universe::verify();
2549 }
2550
2551 // Snapshot the soft reference policy to be used in this collection cycle.
2552 ref_processor()->setup_policy(clear_all_soft_refs);
2553
2554 // Decide if class unloading should be done
2555 update_should_unload_classes();
2556
2557 bool init_mark_was_synchronous = false; // until proven otherwise
2558 while (_collectorState != Idling) {
2559 if (TraceCMSState) {
2560 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2561 Thread::current(), _collectorState);
2562 }
2563 switch (_collectorState) {
2564 case InitialMarking:
2565 register_foreground_gc_start(cause);
2566 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2567 checkpointRootsInitial(false);
2568 assert(_collectorState == Marking, "Collector state should have changed"
2569 " within checkpointRootsInitial()");
2570 break;
2571 case Marking:
2572 // initial marking in checkpointRootsInitialWork has been completed
2573 if (VerifyDuringGC &&
2574 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2575 Universe::verify("Verify before initial mark: ");
2576 }
2577 {
2578 bool res = markFromRoots(false);
2579 assert(res && _collectorState == FinalMarking, "Collector state should "
2580 "have changed");
2581 break;
2582 }
2583 case FinalMarking:
2584 if (VerifyDuringGC &&
2585 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2586 Universe::verify("Verify before re-mark: ");
2587 }
2588 checkpointRootsFinal(false, clear_all_soft_refs,
2589 init_mark_was_synchronous);
2590 assert(_collectorState == Sweeping, "Collector state should not "
2591 "have changed within checkpointRootsFinal()");
2592 break;
2593 case Sweeping:
2594 // final marking in checkpointRootsFinal has been completed
2595 if (VerifyDuringGC &&
2596 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2597 Universe::verify("Verify before sweep: ");
2598 }
2599 sweep(false);
2600 assert(_collectorState == Resizing, "Incorrect state");
2601 break;
2602 case Resizing: {
2603 // Sweeping has been completed; the actual resize in this case
2604 // is done separately; nothing to be done in this state.
2605 _collectorState = Resetting;
2606 break;
2607 }
2608 case Resetting:
2609 // The heap has been resized.
2610 if (VerifyDuringGC &&
2611 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2612 Universe::verify("Verify before reset: ");
2613 }
2614 save_heap_summary();
2615 reset(false);
2616 assert(_collectorState == Idling, "Collector state should "
2617 "have changed");
2618 break;
2619 case Precleaning:
2620 case AbortablePreclean:
2621 // Elide the preclean phase
2622 _collectorState = FinalMarking;
2623 break;
2624 default:
2625 ShouldNotReachHere();
2626 }
2627 if (TraceCMSState) {
2628 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2629 Thread::current(), _collectorState);
2630 }
2631 }
2632
2633 if (UseAdaptiveSizePolicy) {
2634 GenCollectedHeap* gch = GenCollectedHeap::heap();
2635 size_policy()->ms_collection_end(gch->gc_cause());
2636 }
2637
2638 if (VerifyAfterGC &&
2639 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2640 Universe::verify();
2641 }
2642 if (TraceCMSState) {
2643 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2644 " exiting collection CMS state %d",
2645 Thread::current(), _collectorState);
2646 }
2647 }
2648
2649 bool CMSCollector::waitForForegroundGC() {
2650 bool res = false;
2651 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2652 "CMS thread should have CMS token");
2653 // Block the foreground collector until the
2654 // background collectors decides whether to
2655 // yield.
2656 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2657 _foregroundGCShouldWait = true;
2658 if (_foregroundGCIsActive) {
2659 // The background collector yields to the
2660 // foreground collector and returns a value
2661 // indicating that it has yielded. The foreground
2662 // collector can proceed.
2663 res = true;
2664 _foregroundGCShouldWait = false;
2665 ConcurrentMarkSweepThread::clear_CMS_flag(
2666 ConcurrentMarkSweepThread::CMS_cms_has_token);
2667 ConcurrentMarkSweepThread::set_CMS_flag(
2668 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2669 // Get a possibly blocked foreground thread going
2670 CGC_lock->notify();
2671 if (TraceCMSState) {
2672 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2673 Thread::current(), _collectorState);
2674 }
2675 while (_foregroundGCIsActive) {
2676 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2677 }
2678 ConcurrentMarkSweepThread::set_CMS_flag(
2679 ConcurrentMarkSweepThread::CMS_cms_has_token);
2680 ConcurrentMarkSweepThread::clear_CMS_flag(
2681 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2682 }
2683 if (TraceCMSState) {
2684 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2685 Thread::current(), _collectorState);
2686 }
2687 return res;
2688 }
2689
2690 // Because of the need to lock the free lists and other structures in
2691 // the collector, common to all the generations that the collector is
2692 // collecting, we need the gc_prologues of individual CMS generations
2693 // delegate to their collector. It may have been simpler had the
2694 // current infrastructure allowed one to call a prologue on a
2695 // collector. In the absence of that we have the generation's
2696 // prologue delegate to the collector, which delegates back
2697 // some "local" work to a worker method in the individual generations
2698 // that it's responsible for collecting, while itself doing any
2699 // work common to all generations it's responsible for. A similar
2700 // comment applies to the gc_epilogue()'s.
2701 // The role of the variable _between_prologue_and_epilogue is to
2702 // enforce the invocation protocol.
2703 void CMSCollector::gc_prologue(bool full) {
2704 // Call gc_prologue_work() for the CMSGen
2705 // we are responsible for.
2706
2707 // The following locking discipline assumes that we are only called
2708 // when the world is stopped.
2709 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2710
2711 // The CMSCollector prologue must call the gc_prologues for the
2712 // "generations" that it's responsible
2713 // for.
2714
2715 assert( Thread::current()->is_VM_thread()
2716 || ( CMSScavengeBeforeRemark
2717 && Thread::current()->is_ConcurrentGC_thread()),
2718 "Incorrect thread type for prologue execution");
2719
2720 if (_between_prologue_and_epilogue) {
2721 // We have already been invoked; this is a gc_prologue delegation
2722 // from yet another CMS generation that we are responsible for, just
2723 // ignore it since all relevant work has already been done.
2724 return;
2725 }
2726
2727 // set a bit saying prologue has been called; cleared in epilogue
2728 _between_prologue_and_epilogue = true;
2729 // Claim locks for common data structures, then call gc_prologue_work()
2730 // for each CMSGen.
2731
2732 getFreelistLocks(); // gets free list locks on constituent spaces
2733 bitMapLock()->lock_without_safepoint_check();
2734
2735 // Should call gc_prologue_work() for all cms gens we are responsible for
2736 bool duringMarking = _collectorState >= Marking
2737 && _collectorState < Sweeping;
2738
2739 // The young collections clear the modified oops state, which tells if
2740 // there are any modified oops in the class. The remark phase also needs
2741 // that information. Tell the young collection to save the union of all
2742 // modified klasses.
2743 if (duringMarking) {
2744 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2745 }
2746
2747 bool registerClosure = duringMarking;
2748
2749 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2750 &_modUnionClosurePar
2751 : &_modUnionClosure;
2752 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2753
2754 if (!full) {
2755 stats().record_gc0_begin();
2756 }
2757 }
2758
2759 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2760
2761 _capacity_at_prologue = capacity();
2762 _used_at_prologue = used();
2763
2764 // Delegate to CMScollector which knows how to coordinate between
2765 // this and any other CMS generations that it is responsible for
2766 // collecting.
2767 collector()->gc_prologue(full);
2768 }
2769
2770 // This is a "private" interface for use by this generation's CMSCollector.
2771 // Not to be called directly by any other entity (for instance,
2772 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2773 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2774 bool registerClosure, ModUnionClosure* modUnionClosure) {
2775 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2776 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2777 "Should be NULL");
2778 if (registerClosure) {
2779 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2780 }
2781 cmsSpace()->gc_prologue();
2782 // Clear stat counters
2783 NOT_PRODUCT(
2784 assert(_numObjectsPromoted == 0, "check");
2785 assert(_numWordsPromoted == 0, "check");
2786 if (Verbose && PrintGC) {
2787 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2788 SIZE_FORMAT" bytes concurrently",
2789 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2790 }
2791 _numObjectsAllocated = 0;
2792 _numWordsAllocated = 0;
2793 )
2794 }
2795
2796 void CMSCollector::gc_epilogue(bool full) {
2797 // The following locking discipline assumes that we are only called
2798 // when the world is stopped.
2799 assert(SafepointSynchronize::is_at_safepoint(),
2800 "world is stopped assumption");
2801
2802 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2803 // if linear allocation blocks need to be appropriately marked to allow the
2804 // the blocks to be parsable. We also check here whether we need to nudge the
2805 // CMS collector thread to start a new cycle (if it's not already active).
2806 assert( Thread::current()->is_VM_thread()
2807 || ( CMSScavengeBeforeRemark
2808 && Thread::current()->is_ConcurrentGC_thread()),
2809 "Incorrect thread type for epilogue execution");
2810
2811 if (!_between_prologue_and_epilogue) {
2812 // We have already been invoked; this is a gc_epilogue delegation
2813 // from yet another CMS generation that we are responsible for, just
2814 // ignore it since all relevant work has already been done.
2815 return;
2816 }
2817 assert(haveFreelistLocks(), "must have freelist locks");
2818 assert_lock_strong(bitMapLock());
2819
2820 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2821
2822 _cmsGen->gc_epilogue_work(full);
2823
2824 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2825 // in case sampling was not already enabled, enable it
2826 _start_sampling = true;
2827 }
2828 // reset _eden_chunk_array so sampling starts afresh
2829 _eden_chunk_index = 0;
2830
2831 size_t cms_used = _cmsGen->cmsSpace()->used();
2832
2833 // update performance counters - this uses a special version of
2834 // update_counters() that allows the utilization to be passed as a
2835 // parameter, avoiding multiple calls to used().
2836 //
2837 _cmsGen->update_counters(cms_used);
2838
2839 if (CMSIncrementalMode) {
2840 icms_update_allocation_limits();
2841 }
2842
2843 bitMapLock()->unlock();
2844 releaseFreelistLocks();
2845
2846 if (!CleanChunkPoolAsync) {
2847 Chunk::clean_chunk_pool();
2848 }
2849
2850 set_did_compact(false);
2851 _between_prologue_and_epilogue = false; // ready for next cycle
2852 }
2853
2854 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2855 collector()->gc_epilogue(full);
2856
2857 // Also reset promotion tracking in par gc thread states.
2858 if (CollectedHeap::use_parallel_gc_threads()) {
2859 for (uint i = 0; i < ParallelGCThreads; i++) {
2860 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2861 }
2862 }
2863 }
2864
2865 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2866 assert(!incremental_collection_failed(), "Should have been cleared");
2867 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2868 cmsSpace()->gc_epilogue();
2869 // Print stat counters
2870 NOT_PRODUCT(
2871 assert(_numObjectsAllocated == 0, "check");
2872 assert(_numWordsAllocated == 0, "check");
2873 if (Verbose && PrintGC) {
2874 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2875 SIZE_FORMAT" bytes",
2876 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2877 }
2878 _numObjectsPromoted = 0;
2879 _numWordsPromoted = 0;
2880 )
2881
2882 if (PrintGC && Verbose) {
2883 // Call down the chain in contiguous_available needs the freelistLock
2884 // so print this out before releasing the freeListLock.
2885 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2886 contiguous_available());
2887 }
2888 }
2889
2890 #ifndef PRODUCT
2891 bool CMSCollector::have_cms_token() {
2892 Thread* thr = Thread::current();
2893 if (thr->is_VM_thread()) {
2894 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2895 } else if (thr->is_ConcurrentGC_thread()) {
2896 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2897 } else if (thr->is_GC_task_thread()) {
2898 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2899 ParGCRareEvent_lock->owned_by_self();
2900 }
2901 return false;
2902 }
2903 #endif
2904
2905 // Check reachability of the given heap address in CMS generation,
2906 // treating all other generations as roots.
2907 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2908 // We could "guarantee" below, rather than assert, but I'll
2909 // leave these as "asserts" so that an adventurous debugger
2910 // could try this in the product build provided some subset of
2911 // the conditions were met, provided they were interested in the
2912 // results and knew that the computation below wouldn't interfere
2913 // with other concurrent computations mutating the structures
2914 // being read or written.
2915 assert(SafepointSynchronize::is_at_safepoint(),
2916 "Else mutations in object graph will make answer suspect");
2917 assert(have_cms_token(), "Should hold cms token");
2918 assert(haveFreelistLocks(), "must hold free list locks");
2919 assert_lock_strong(bitMapLock());
2920
2921 // Clear the marking bit map array before starting, but, just
2922 // for kicks, first report if the given address is already marked
2923 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", addr,
2924 _markBitMap.isMarked(addr) ? "" : " not");
2925
2926 if (verify_after_remark()) {
2927 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2928 bool result = verification_mark_bm()->isMarked(addr);
2929 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", addr,
2930 result ? "IS" : "is NOT");
2931 return result;
2932 } else {
2933 gclog_or_tty->print_cr("Could not compute result");
2934 return false;
2935 }
2936 }
2937
2938
2939 void
2940 CMSCollector::print_on_error(outputStream* st) {
2941 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2942 if (collector != NULL) {
2943 CMSBitMap* bitmap = &collector->_markBitMap;
2944 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2945 bitmap->print_on_error(st, " Bits: ");
2946
2947 st->cr();
2948
2949 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2950 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2951 mut_bitmap->print_on_error(st, " Bits: ");
2952 }
2953 }
2954
2955 ////////////////////////////////////////////////////////
2956 // CMS Verification Support
2957 ////////////////////////////////////////////////////////
2958 // Following the remark phase, the following invariant
2959 // should hold -- each object in the CMS heap which is
2960 // marked in markBitMap() should be marked in the verification_mark_bm().
2961
2962 class VerifyMarkedClosure: public BitMapClosure {
2963 CMSBitMap* _marks;
2964 bool _failed;
2965
2966 public:
2967 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2968
2969 bool do_bit(size_t offset) {
2970 HeapWord* addr = _marks->offsetToHeapWord(offset);
2971 if (!_marks->isMarked(addr)) {
2972 oop(addr)->print_on(gclog_or_tty);
2973 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2974 _failed = true;
2975 }
2976 return true;
2977 }
2978
2979 bool failed() { return _failed; }
2980 };
2981
2982 bool CMSCollector::verify_after_remark(bool silent) {
2983 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2984 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2985 static bool init = false;
2986
2987 assert(SafepointSynchronize::is_at_safepoint(),
2988 "Else mutations in object graph will make answer suspect");
2989 assert(have_cms_token(),
2990 "Else there may be mutual interference in use of "
2991 " verification data structures");
2992 assert(_collectorState > Marking && _collectorState <= Sweeping,
2993 "Else marking info checked here may be obsolete");
2994 assert(haveFreelistLocks(), "must hold free list locks");
2995 assert_lock_strong(bitMapLock());
2996
2997
2998 // Allocate marking bit map if not already allocated
2999 if (!init) { // first time
3000 if (!verification_mark_bm()->allocate(_span)) {
3001 return false;
3002 }
3003 init = true;
3004 }
3005
3006 assert(verification_mark_stack()->isEmpty(), "Should be empty");
3007
3008 // Turn off refs discovery -- so we will be tracing through refs.
3009 // This is as intended, because by this time
3010 // GC must already have cleared any refs that need to be cleared,
3011 // and traced those that need to be marked; moreover,
3012 // the marking done here is not going to interfere in any
3013 // way with the marking information used by GC.
3014 NoRefDiscovery no_discovery(ref_processor());
3015
3016 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3017
3018 // Clear any marks from a previous round
3019 verification_mark_bm()->clear_all();
3020 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
3021 verify_work_stacks_empty();
3022
3023 GenCollectedHeap* gch = GenCollectedHeap::heap();
3024 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3025 // Update the saved marks which may affect the root scans.
3026 gch->save_marks();
3027
3028 if (CMSRemarkVerifyVariant == 1) {
3029 // In this first variant of verification, we complete
3030 // all marking, then check if the new marks-vector is
3031 // a subset of the CMS marks-vector.
3032 verify_after_remark_work_1();
3033 } else if (CMSRemarkVerifyVariant == 2) {
3034 // In this second variant of verification, we flag an error
3035 // (i.e. an object reachable in the new marks-vector not reachable
3036 // in the CMS marks-vector) immediately, also indicating the
3037 // identify of an object (A) that references the unmarked object (B) --
3038 // presumably, a mutation to A failed to be picked up by preclean/remark?
3039 verify_after_remark_work_2();
3040 } else {
3041 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3042 CMSRemarkVerifyVariant);
3043 }
3044 if (!silent) gclog_or_tty->print(" done] ");
3045 return true;
3046 }
3047
3048 void CMSCollector::verify_after_remark_work_1() {
3049 ResourceMark rm;
3050 HandleMark hm;
3051 GenCollectedHeap* gch = GenCollectedHeap::heap();
3052
3053 // Get a clear set of claim bits for the strong roots processing to work with.
3054 ClassLoaderDataGraph::clear_claimed_marks();
3055
3056 // Mark from roots one level into CMS
3057 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3058 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3059
3060 gch->gen_process_strong_roots(_cmsGen->level(),
3061 true, // younger gens are roots
3062 true, // activate StrongRootsScope
3063 SharedHeap::ScanningOption(roots_scanning_options()),
3064 ¬Older,
3065 NULL,
3066 NULL); // SSS: Provide correct closure
3067
3068 // Now mark from the roots
3069 MarkFromRootsClosure markFromRootsClosure(this, _span,
3070 verification_mark_bm(), verification_mark_stack(),
3071 false /* don't yield */, true /* verifying */);
3072 assert(_restart_addr == NULL, "Expected pre-condition");
3073 verification_mark_bm()->iterate(&markFromRootsClosure);
3074 while (_restart_addr != NULL) {
3075 // Deal with stack overflow: by restarting at the indicated
3076 // address.
3077 HeapWord* ra = _restart_addr;
3078 markFromRootsClosure.reset(ra);
3079 _restart_addr = NULL;
3080 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3081 }
3082 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3083 verify_work_stacks_empty();
3084
3085 // Marking completed -- now verify that each bit marked in
3086 // verification_mark_bm() is also marked in markBitMap(); flag all
3087 // errors by printing corresponding objects.
3088 VerifyMarkedClosure vcl(markBitMap());
3089 verification_mark_bm()->iterate(&vcl);
3090 if (vcl.failed()) {
3091 gclog_or_tty->print("Verification failed");
3092 Universe::heap()->print_on(gclog_or_tty);
3093 fatal("CMS: failed marking verification after remark");
3094 }
3095 }
3096
3097 class VerifyKlassOopsKlassClosure : public KlassClosure {
3098 class VerifyKlassOopsClosure : public OopClosure {
3099 CMSBitMap* _bitmap;
3100 public:
3101 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3102 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3103 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3104 } _oop_closure;
3105 public:
3106 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3107 void do_klass(Klass* k) {
3108 k->oops_do(&_oop_closure);
3109 }
3110 };
3111
3112 void CMSCollector::verify_after_remark_work_2() {
3113 ResourceMark rm;
3114 HandleMark hm;
3115 GenCollectedHeap* gch = GenCollectedHeap::heap();
3116
3117 // Get a clear set of claim bits for the strong roots processing to work with.
3118 ClassLoaderDataGraph::clear_claimed_marks();
3119
3120 // Mark from roots one level into CMS
3121 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3122 markBitMap());
3123 CMKlassClosure klass_closure(¬Older);
3124
3125 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3126 gch->gen_process_strong_roots(_cmsGen->level(),
3127 true, // younger gens are roots
3128 true, // activate StrongRootsScope
3129 SharedHeap::ScanningOption(roots_scanning_options()),
3130 ¬Older,
3131 NULL,
3132 &klass_closure);
3133
3134 // Now mark from the roots
3135 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3136 verification_mark_bm(), markBitMap(), verification_mark_stack());
3137 assert(_restart_addr == NULL, "Expected pre-condition");
3138 verification_mark_bm()->iterate(&markFromRootsClosure);
3139 while (_restart_addr != NULL) {
3140 // Deal with stack overflow: by restarting at the indicated
3141 // address.
3142 HeapWord* ra = _restart_addr;
3143 markFromRootsClosure.reset(ra);
3144 _restart_addr = NULL;
3145 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3146 }
3147 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3148 verify_work_stacks_empty();
3149
3150 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3151 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3152
3153 // Marking completed -- now verify that each bit marked in
3154 // verification_mark_bm() is also marked in markBitMap(); flag all
3155 // errors by printing corresponding objects.
3156 VerifyMarkedClosure vcl(markBitMap());
3157 verification_mark_bm()->iterate(&vcl);
3158 assert(!vcl.failed(), "Else verification above should not have succeeded");
3159 }
3160
3161 void ConcurrentMarkSweepGeneration::save_marks() {
3162 // delegate to CMS space
3163 cmsSpace()->save_marks();
3164 for (uint i = 0; i < ParallelGCThreads; i++) {
3165 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3166 }
3167 }
3168
3169 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3170 return cmsSpace()->no_allocs_since_save_marks();
3171 }
3172
3173 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3174 \
3175 void ConcurrentMarkSweepGeneration:: \
3176 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3177 cl->set_generation(this); \
3178 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3179 cl->reset_generation(); \
3180 save_marks(); \
3181 }
3182
3183 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3184
3185 void
3186 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3187 cl->set_generation(this);
3188 younger_refs_in_space_iterate(_cmsSpace, cl);
3189 cl->reset_generation();
3190 }
3191
3192 void
3193 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3194 if (freelistLock()->owned_by_self()) {
3195 Generation::oop_iterate(cl);
3196 } else {
3197 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3198 Generation::oop_iterate(cl);
3199 }
3200 }
3201
3202 void
3203 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3204 if (freelistLock()->owned_by_self()) {
3205 Generation::object_iterate(cl);
3206 } else {
3207 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3208 Generation::object_iterate(cl);
3209 }
3210 }
3211
3212 void
3213 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3214 if (freelistLock()->owned_by_self()) {
3215 Generation::safe_object_iterate(cl);
3216 } else {
3217 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3218 Generation::safe_object_iterate(cl);
3219 }
3220 }
3221
3222 void
3223 ConcurrentMarkSweepGeneration::post_compact() {
3224 }
3225
3226 void
3227 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3228 // Fix the linear allocation blocks to look like free blocks.
3229
3230 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3231 // are not called when the heap is verified during universe initialization and
3232 // at vm shutdown.
3233 if (freelistLock()->owned_by_self()) {
3234 cmsSpace()->prepare_for_verify();
3235 } else {
3236 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3237 cmsSpace()->prepare_for_verify();
3238 }
3239 }
3240
3241 void
3242 ConcurrentMarkSweepGeneration::verify() {
3243 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3244 // are not called when the heap is verified during universe initialization and
3245 // at vm shutdown.
3246 if (freelistLock()->owned_by_self()) {
3247 cmsSpace()->verify();
3248 } else {
3249 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3250 cmsSpace()->verify();
3251 }
3252 }
3253
3254 void CMSCollector::verify() {
3255 _cmsGen->verify();
3256 }
3257
3258 #ifndef PRODUCT
3259 bool CMSCollector::overflow_list_is_empty() const {
3260 assert(_num_par_pushes >= 0, "Inconsistency");
3261 if (_overflow_list == NULL) {
3262 assert(_num_par_pushes == 0, "Inconsistency");
3263 }
3264 return _overflow_list == NULL;
3265 }
3266
3267 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3268 // merely consolidate assertion checks that appear to occur together frequently.
3269 void CMSCollector::verify_work_stacks_empty() const {
3270 assert(_markStack.isEmpty(), "Marking stack should be empty");
3271 assert(overflow_list_is_empty(), "Overflow list should be empty");
3272 }
3273
3274 void CMSCollector::verify_overflow_empty() const {
3275 assert(overflow_list_is_empty(), "Overflow list should be empty");
3276 assert(no_preserved_marks(), "No preserved marks");
3277 }
3278 #endif // PRODUCT
3279
3280 // Decide if we want to enable class unloading as part of the
3281 // ensuing concurrent GC cycle. We will collect and
3282 // unload classes if it's the case that:
3283 // (1) an explicit gc request has been made and the flag
3284 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3285 // (2) (a) class unloading is enabled at the command line, and
3286 // (b) old gen is getting really full
3287 // NOTE: Provided there is no change in the state of the heap between
3288 // calls to this method, it should have idempotent results. Moreover,
3289 // its results should be monotonically increasing (i.e. going from 0 to 1,
3290 // but not 1 to 0) between successive calls between which the heap was
3291 // not collected. For the implementation below, it must thus rely on
3292 // the property that concurrent_cycles_since_last_unload()
3293 // will not decrease unless a collection cycle happened and that
3294 // _cmsGen->is_too_full() are
3295 // themselves also monotonic in that sense. See check_monotonicity()
3296 // below.
3297 void CMSCollector::update_should_unload_classes() {
3298 _should_unload_classes = false;
3299 // Condition 1 above
3300 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3301 _should_unload_classes = true;
3302 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3303 // Disjuncts 2.b.(i,ii,iii) above
3304 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3305 CMSClassUnloadingMaxInterval)
3306 || _cmsGen->is_too_full();
3307 }
3308 }
3309
3310 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3311 bool res = should_concurrent_collect();
3312 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3313 return res;
3314 }
3315
3316 void CMSCollector::setup_cms_unloading_and_verification_state() {
3317 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3318 || VerifyBeforeExit;
3319 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_AllCodeCache;
3320
3321 // We set the proper root for this CMS cycle here.
3322 if (should_unload_classes()) { // Should unload classes this cycle
3323 remove_root_scanning_option(SharedHeap::SO_AllClasses);
3324 add_root_scanning_option(SharedHeap::SO_SystemClasses);
3325 remove_root_scanning_option(rso); // Shrink the root set appropriately
3326 set_verifying(should_verify); // Set verification state for this cycle
3327 return; // Nothing else needs to be done at this time
3328 }
3329
3330 // Not unloading classes this cycle
3331 assert(!should_unload_classes(), "Inconsistency!");
3332 remove_root_scanning_option(SharedHeap::SO_SystemClasses);
3333 add_root_scanning_option(SharedHeap::SO_AllClasses);
3334
3335 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3336 // Include symbols, strings and code cache elements to prevent their resurrection.
3337 add_root_scanning_option(rso);
3338 set_verifying(true);
3339 } else if (verifying() && !should_verify) {
3340 // We were verifying, but some verification flags got disabled.
3341 set_verifying(false);
3342 // Exclude symbols, strings and code cache elements from root scanning to
3343 // reduce IM and RM pauses.
3344 remove_root_scanning_option(rso);
3345 }
3346 }
3347
3348
3349 #ifndef PRODUCT
3350 HeapWord* CMSCollector::block_start(const void* p) const {
3351 const HeapWord* addr = (HeapWord*)p;
3352 if (_span.contains(p)) {
3353 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3354 return _cmsGen->cmsSpace()->block_start(p);
3355 }
3356 }
3357 return NULL;
3358 }
3359 #endif
3360
3361 HeapWord*
3362 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3363 bool tlab,
3364 bool parallel) {
3365 CMSSynchronousYieldRequest yr;
3366 assert(!tlab, "Can't deal with TLAB allocation");
3367 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3368 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3369 CMSExpansionCause::_satisfy_allocation);
3370 if (GCExpandToAllocateDelayMillis > 0) {
3371 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3372 }
3373 return have_lock_and_allocate(word_size, tlab);
3374 }
3375
3376 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3377 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3378 // to CardGeneration and share it...
3379 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3380 return CardGeneration::expand(bytes, expand_bytes);
3381 }
3382
3383 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3384 CMSExpansionCause::Cause cause)
3385 {
3386
3387 bool success = expand(bytes, expand_bytes);
3388
3389 // remember why we expanded; this information is used
3390 // by shouldConcurrentCollect() when making decisions on whether to start
3391 // a new CMS cycle.
3392 if (success) {
3393 set_expansion_cause(cause);
3394 if (PrintGCDetails && Verbose) {
3395 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3396 CMSExpansionCause::to_string(cause));
3397 }
3398 }
3399 }
3400
3401 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3402 HeapWord* res = NULL;
3403 MutexLocker x(ParGCRareEvent_lock);
3404 while (true) {
3405 // Expansion by some other thread might make alloc OK now:
3406 res = ps->lab.alloc(word_sz);
3407 if (res != NULL) return res;
3408 // If there's not enough expansion space available, give up.
3409 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3410 return NULL;
3411 }
3412 // Otherwise, we try expansion.
3413 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3414 CMSExpansionCause::_allocate_par_lab);
3415 // Now go around the loop and try alloc again;
3416 // A competing par_promote might beat us to the expansion space,
3417 // so we may go around the loop again if promotion fails again.
3418 if (GCExpandToAllocateDelayMillis > 0) {
3419 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3420 }
3421 }
3422 }
3423
3424
3425 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3426 PromotionInfo* promo) {
3427 MutexLocker x(ParGCRareEvent_lock);
3428 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3429 while (true) {
3430 // Expansion by some other thread might make alloc OK now:
3431 if (promo->ensure_spooling_space()) {
3432 assert(promo->has_spooling_space(),
3433 "Post-condition of successful ensure_spooling_space()");
3434 return true;
3435 }
3436 // If there's not enough expansion space available, give up.
3437 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3438 return false;
3439 }
3440 // Otherwise, we try expansion.
3441 expand(refill_size_bytes, MinHeapDeltaBytes,
3442 CMSExpansionCause::_allocate_par_spooling_space);
3443 // Now go around the loop and try alloc again;
3444 // A competing allocation might beat us to the expansion space,
3445 // so we may go around the loop again if allocation fails again.
3446 if (GCExpandToAllocateDelayMillis > 0) {
3447 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3448 }
3449 }
3450 }
3451
3452
3453 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3454 assert_locked_or_safepoint(ExpandHeap_lock);
3455 // Shrink committed space
3456 _virtual_space.shrink_by(bytes);
3457 // Shrink space; this also shrinks the space's BOT
3458 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3459 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3460 // Shrink the shared block offset array
3461 _bts->resize(new_word_size);
3462 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3463 // Shrink the card table
3464 Universe::heap()->barrier_set()->resize_covered_region(mr);
3465
3466 if (Verbose && PrintGC) {
3467 size_t new_mem_size = _virtual_space.committed_size();
3468 size_t old_mem_size = new_mem_size + bytes;
3469 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3470 name(), old_mem_size/K, new_mem_size/K);
3471 }
3472 }
3473
3474 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3475 assert_locked_or_safepoint(Heap_lock);
3476 size_t size = ReservedSpace::page_align_size_down(bytes);
3477 // Only shrink if a compaction was done so that all the free space
3478 // in the generation is in a contiguous block at the end.
3479 if (size > 0 && did_compact()) {
3480 shrink_by(size);
3481 }
3482 }
3483
3484 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3485 assert_locked_or_safepoint(Heap_lock);
3486 bool result = _virtual_space.expand_by(bytes);
3487 if (result) {
3488 size_t new_word_size =
3489 heap_word_size(_virtual_space.committed_size());
3490 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3491 _bts->resize(new_word_size); // resize the block offset shared array
3492 Universe::heap()->barrier_set()->resize_covered_region(mr);
3493 // Hmmmm... why doesn't CFLS::set_end verify locking?
3494 // This is quite ugly; FIX ME XXX
3495 _cmsSpace->assert_locked(freelistLock());
3496 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3497
3498 // update the space and generation capacity counters
3499 if (UsePerfData) {
3500 _space_counters->update_capacity();
3501 _gen_counters->update_all();
3502 }
3503
3504 if (Verbose && PrintGC) {
3505 size_t new_mem_size = _virtual_space.committed_size();
3506 size_t old_mem_size = new_mem_size - bytes;
3507 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3508 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3509 }
3510 }
3511 return result;
3512 }
3513
3514 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3515 assert_locked_or_safepoint(Heap_lock);
3516 bool success = true;
3517 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3518 if (remaining_bytes > 0) {
3519 success = grow_by(remaining_bytes);
3520 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3521 }
3522 return success;
3523 }
3524
3525 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3526 assert_locked_or_safepoint(Heap_lock);
3527 assert_lock_strong(freelistLock());
3528 if (PrintGCDetails && Verbose) {
3529 warning("Shrinking of CMS not yet implemented");
3530 }
3531 return;
3532 }
3533
3534
3535 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3536 // phases.
3537 class CMSPhaseAccounting: public StackObj {
3538 public:
3539 CMSPhaseAccounting(CMSCollector *collector,
3540 const char *phase,
3541 bool print_cr = true);
3542 ~CMSPhaseAccounting();
3543
3544 private:
3545 CMSCollector *_collector;
3546 const char *_phase;
3547 elapsedTimer _wallclock;
3548 bool _print_cr;
3549
3550 public:
3551 // Not MT-safe; so do not pass around these StackObj's
3552 // where they may be accessed by other threads.
3553 jlong wallclock_millis() {
3554 assert(_wallclock.is_active(), "Wall clock should not stop");
3555 _wallclock.stop(); // to record time
3556 jlong ret = _wallclock.milliseconds();
3557 _wallclock.start(); // restart
3558 return ret;
3559 }
3560 };
3561
3562 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3563 const char *phase,
3564 bool print_cr) :
3565 _collector(collector), _phase(phase), _print_cr(print_cr) {
3566
3567 if (PrintCMSStatistics != 0) {
3568 _collector->resetYields();
3569 }
3570 if (PrintGCDetails) {
3571 gclog_or_tty->date_stamp(PrintGCDateStamps);
3572 gclog_or_tty->stamp(PrintGCTimeStamps);
3573 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3574 _collector->cmsGen()->short_name(), _phase);
3575 }
3576 _collector->resetTimer();
3577 _wallclock.start();
3578 _collector->startTimer();
3579 }
3580
3581 CMSPhaseAccounting::~CMSPhaseAccounting() {
3582 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3583 _collector->stopTimer();
3584 _wallclock.stop();
3585 if (PrintGCDetails) {
3586 gclog_or_tty->date_stamp(PrintGCDateStamps);
3587 gclog_or_tty->stamp(PrintGCTimeStamps);
3588 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3589 _collector->cmsGen()->short_name(),
3590 _phase, _collector->timerValue(), _wallclock.seconds());
3591 if (_print_cr) {
3592 gclog_or_tty->cr();
3593 }
3594 if (PrintCMSStatistics != 0) {
3595 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3596 _collector->yields());
3597 }
3598 }
3599 }
3600
3601 // CMS work
3602
3603 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3604 class CMSParMarkTask : public AbstractGangTask {
3605 protected:
3606 CMSCollector* _collector;
3607 int _n_workers;
3608 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3609 AbstractGangTask(name),
3610 _collector(collector),
3611 _n_workers(n_workers) {}
3612 // Work method in support of parallel rescan ... of young gen spaces
3613 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3614 ContiguousSpace* space,
3615 HeapWord** chunk_array, size_t chunk_top);
3616 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3617 };
3618
3619 // Parallel initial mark task
3620 class CMSParInitialMarkTask: public CMSParMarkTask {
3621 public:
3622 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3623 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3624 collector, n_workers) {}
3625 void work(uint worker_id);
3626 };
3627
3628 // Checkpoint the roots into this generation from outside
3629 // this generation. [Note this initial checkpoint need only
3630 // be approximate -- we'll do a catch up phase subsequently.]
3631 void CMSCollector::checkpointRootsInitial(bool asynch) {
3632 assert(_collectorState == InitialMarking, "Wrong collector state");
3633 check_correct_thread_executing();
3634 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3635
3636 save_heap_summary();
3637 report_heap_summary(GCWhen::BeforeGC);
3638
3639 ReferenceProcessor* rp = ref_processor();
3640 SpecializationStats::clear();
3641 assert(_restart_addr == NULL, "Control point invariant");
3642 if (asynch) {
3643 // acquire locks for subsequent manipulations
3644 MutexLockerEx x(bitMapLock(),
3645 Mutex::_no_safepoint_check_flag);
3646 checkpointRootsInitialWork(asynch);
3647 // enable ("weak") refs discovery
3648 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3649 _collectorState = Marking;
3650 } else {
3651 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3652 // which recognizes if we are a CMS generation, and doesn't try to turn on
3653 // discovery; verify that they aren't meddling.
3654 assert(!rp->discovery_is_atomic(),
3655 "incorrect setting of discovery predicate");
3656 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3657 "ref discovery for this generation kind");
3658 // already have locks
3659 checkpointRootsInitialWork(asynch);
3660 // now enable ("weak") refs discovery
3661 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3662 _collectorState = Marking;
3663 }
3664 SpecializationStats::print();
3665 }
3666
3667 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3668 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3669 assert(_collectorState == InitialMarking, "just checking");
3670
3671 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3672 // precede our marking with a collection of all
3673 // younger generations to keep floating garbage to a minimum.
3674 // XXX: we won't do this for now -- it's an optimization to be done later.
3675
3676 // already have locks
3677 assert_lock_strong(bitMapLock());
3678 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3679
3680 // Setup the verification and class unloading state for this
3681 // CMS collection cycle.
3682 setup_cms_unloading_and_verification_state();
3683
3684 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3685 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3686 if (UseAdaptiveSizePolicy) {
3687 size_policy()->checkpoint_roots_initial_begin();
3688 }
3689
3690 // Reset all the PLAB chunk arrays if necessary.
3691 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3692 reset_survivor_plab_arrays();
3693 }
3694
3695 ResourceMark rm;
3696 HandleMark hm;
3697
3698 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3699 GenCollectedHeap* gch = GenCollectedHeap::heap();
3700
3701 verify_work_stacks_empty();
3702 verify_overflow_empty();
3703
3704 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3705 // Update the saved marks which may affect the root scans.
3706 gch->save_marks();
3707
3708 // weak reference processing has not started yet.
3709 ref_processor()->set_enqueuing_is_done(false);
3710
3711 // Need to remember all newly created CLDs,
3712 // so that we can guarantee that the remark finds them.
3713 ClassLoaderDataGraph::remember_new_clds(true);
3714
3715 // Whenever a CLD is found, it will be claimed before proceeding to mark
3716 // the klasses. The claimed marks need to be cleared before marking starts.
3717 ClassLoaderDataGraph::clear_claimed_marks();
3718
3719 if (CMSPrintEdenSurvivorChunks) {
3720 print_eden_and_survivor_chunk_arrays();
3721 }
3722
3723 {
3724 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3725 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3726 // The parallel version.
3727 FlexibleWorkGang* workers = gch->workers();
3728 assert(workers != NULL, "Need parallel worker threads.");
3729 int n_workers = workers->active_workers();
3730 CMSParInitialMarkTask tsk(this, n_workers);
3731 gch->set_par_threads(n_workers);
3732 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3733 if (n_workers > 1) {
3734 GenCollectedHeap::StrongRootsScope srs(gch);
3735 workers->run_task(&tsk);
3736 } else {
3737 GenCollectedHeap::StrongRootsScope srs(gch);
3738 tsk.work(0);
3739 }
3740 gch->set_par_threads(0);
3741 } else {
3742 // The serial version.
3743 CMKlassClosure klass_closure(¬Older);
3744 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3745 gch->gen_process_strong_roots(_cmsGen->level(),
3746 true, // younger gens are roots
3747 true, // activate StrongRootsScope
3748 SharedHeap::ScanningOption(roots_scanning_options()),
3749 ¬Older,
3750 NULL,
3751 &klass_closure);
3752 }
3753 }
3754
3755 // Clear mod-union table; it will be dirtied in the prologue of
3756 // CMS generation per each younger generation collection.
3757
3758 assert(_modUnionTable.isAllClear(),
3759 "Was cleared in most recent final checkpoint phase"
3760 " or no bits are set in the gc_prologue before the start of the next "
3761 "subsequent marking phase.");
3762
3763 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3764
3765 // Save the end of the used_region of the constituent generations
3766 // to be used to limit the extent of sweep in each generation.
3767 save_sweep_limits();
3768 if (UseAdaptiveSizePolicy) {
3769 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3770 }
3771 verify_overflow_empty();
3772 }
3773
3774 bool CMSCollector::markFromRoots(bool asynch) {
3775 // we might be tempted to assert that:
3776 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3777 // "inconsistent argument?");
3778 // However that wouldn't be right, because it's possible that
3779 // a safepoint is indeed in progress as a younger generation
3780 // stop-the-world GC happens even as we mark in this generation.
3781 assert(_collectorState == Marking, "inconsistent state?");
3782 check_correct_thread_executing();
3783 verify_overflow_empty();
3784
3785 bool res;
3786 if (asynch) {
3787
3788 // Start the timers for adaptive size policy for the concurrent phases
3789 // Do it here so that the foreground MS can use the concurrent
3790 // timer since a foreground MS might has the sweep done concurrently
3791 // or STW.
3792 if (UseAdaptiveSizePolicy) {
3793 size_policy()->concurrent_marking_begin();
3794 }
3795
3796 // Weak ref discovery note: We may be discovering weak
3797 // refs in this generation concurrent (but interleaved) with
3798 // weak ref discovery by a younger generation collector.
3799
3800 CMSTokenSyncWithLocks ts(true, bitMapLock());
3801 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3802 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3803 res = markFromRootsWork(asynch);
3804 if (res) {
3805 _collectorState = Precleaning;
3806 } else { // We failed and a foreground collection wants to take over
3807 assert(_foregroundGCIsActive, "internal state inconsistency");
3808 assert(_restart_addr == NULL, "foreground will restart from scratch");
3809 if (PrintGCDetails) {
3810 gclog_or_tty->print_cr("bailing out to foreground collection");
3811 }
3812 }
3813 if (UseAdaptiveSizePolicy) {
3814 size_policy()->concurrent_marking_end();
3815 }
3816 } else {
3817 assert(SafepointSynchronize::is_at_safepoint(),
3818 "inconsistent with asynch == false");
3819 if (UseAdaptiveSizePolicy) {
3820 size_policy()->ms_collection_marking_begin();
3821 }
3822 // already have locks
3823 res = markFromRootsWork(asynch);
3824 _collectorState = FinalMarking;
3825 if (UseAdaptiveSizePolicy) {
3826 GenCollectedHeap* gch = GenCollectedHeap::heap();
3827 size_policy()->ms_collection_marking_end(gch->gc_cause());
3828 }
3829 }
3830 verify_overflow_empty();
3831 return res;
3832 }
3833
3834 bool CMSCollector::markFromRootsWork(bool asynch) {
3835 // iterate over marked bits in bit map, doing a full scan and mark
3836 // from these roots using the following algorithm:
3837 // . if oop is to the right of the current scan pointer,
3838 // mark corresponding bit (we'll process it later)
3839 // . else (oop is to left of current scan pointer)
3840 // push oop on marking stack
3841 // . drain the marking stack
3842
3843 // Note that when we do a marking step we need to hold the
3844 // bit map lock -- recall that direct allocation (by mutators)
3845 // and promotion (by younger generation collectors) is also
3846 // marking the bit map. [the so-called allocate live policy.]
3847 // Because the implementation of bit map marking is not
3848 // robust wrt simultaneous marking of bits in the same word,
3849 // we need to make sure that there is no such interference
3850 // between concurrent such updates.
3851
3852 // already have locks
3853 assert_lock_strong(bitMapLock());
3854
3855 verify_work_stacks_empty();
3856 verify_overflow_empty();
3857 bool result = false;
3858 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3859 result = do_marking_mt(asynch);
3860 } else {
3861 result = do_marking_st(asynch);
3862 }
3863 return result;
3864 }
3865
3866 // Forward decl
3867 class CMSConcMarkingTask;
3868
3869 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3870 CMSCollector* _collector;
3871 CMSConcMarkingTask* _task;
3872 public:
3873 virtual void yield();
3874
3875 // "n_threads" is the number of threads to be terminated.
3876 // "queue_set" is a set of work queues of other threads.
3877 // "collector" is the CMS collector associated with this task terminator.
3878 // "yield" indicates whether we need the gang as a whole to yield.
3879 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3880 ParallelTaskTerminator(n_threads, queue_set),
3881 _collector(collector) { }
3882
3883 void set_task(CMSConcMarkingTask* task) {
3884 _task = task;
3885 }
3886 };
3887
3888 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3889 CMSConcMarkingTask* _task;
3890 public:
3891 bool should_exit_termination();
3892 void set_task(CMSConcMarkingTask* task) {
3893 _task = task;
3894 }
3895 };
3896
3897 // MT Concurrent Marking Task
3898 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3899 CMSCollector* _collector;
3900 int _n_workers; // requested/desired # workers
3901 bool _asynch;
3902 bool _result;
3903 CompactibleFreeListSpace* _cms_space;
3904 char _pad_front[64]; // padding to ...
3905 HeapWord* _global_finger; // ... avoid sharing cache line
3906 char _pad_back[64];
3907 HeapWord* _restart_addr;
3908
3909 // Exposed here for yielding support
3910 Mutex* const _bit_map_lock;
3911
3912 // The per thread work queues, available here for stealing
3913 OopTaskQueueSet* _task_queues;
3914
3915 // Termination (and yielding) support
3916 CMSConcMarkingTerminator _term;
3917 CMSConcMarkingTerminatorTerminator _term_term;
3918
3919 public:
3920 CMSConcMarkingTask(CMSCollector* collector,
3921 CompactibleFreeListSpace* cms_space,
3922 bool asynch,
3923 YieldingFlexibleWorkGang* workers,
3924 OopTaskQueueSet* task_queues):
3925 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3926 _collector(collector),
3927 _cms_space(cms_space),
3928 _asynch(asynch), _n_workers(0), _result(true),
3929 _task_queues(task_queues),
3930 _term(_n_workers, task_queues, _collector),
3931 _bit_map_lock(collector->bitMapLock())
3932 {
3933 _requested_size = _n_workers;
3934 _term.set_task(this);
3935 _term_term.set_task(this);
3936 _restart_addr = _global_finger = _cms_space->bottom();
3937 }
3938
3939
3940 OopTaskQueueSet* task_queues() { return _task_queues; }
3941
3942 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3943
3944 HeapWord** global_finger_addr() { return &_global_finger; }
3945
3946 CMSConcMarkingTerminator* terminator() { return &_term; }
3947
3948 virtual void set_for_termination(int active_workers) {
3949 terminator()->reset_for_reuse(active_workers);
3950 }
3951
3952 void work(uint worker_id);
3953 bool should_yield() {
3954 return ConcurrentMarkSweepThread::should_yield()
3955 && !_collector->foregroundGCIsActive()
3956 && _asynch;
3957 }
3958
3959 virtual void coordinator_yield(); // stuff done by coordinator
3960 bool result() { return _result; }
3961
3962 void reset(HeapWord* ra) {
3963 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3964 _restart_addr = _global_finger = ra;
3965 _term.reset_for_reuse();
3966 }
3967
3968 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3969 OopTaskQueue* work_q);
3970
3971 private:
3972 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3973 void do_work_steal(int i);
3974 void bump_global_finger(HeapWord* f);
3975 };
3976
3977 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3978 assert(_task != NULL, "Error");
3979 return _task->yielding();
3980 // Note that we do not need the disjunct || _task->should_yield() above
3981 // because we want terminating threads to yield only if the task
3982 // is already in the midst of yielding, which happens only after at least one
3983 // thread has yielded.
3984 }
3985
3986 void CMSConcMarkingTerminator::yield() {
3987 if (_task->should_yield()) {
3988 _task->yield();
3989 } else {
3990 ParallelTaskTerminator::yield();
3991 }
3992 }
3993
3994 ////////////////////////////////////////////////////////////////
3995 // Concurrent Marking Algorithm Sketch
3996 ////////////////////////////////////////////////////////////////
3997 // Until all tasks exhausted (both spaces):
3998 // -- claim next available chunk
3999 // -- bump global finger via CAS
4000 // -- find first object that starts in this chunk
4001 // and start scanning bitmap from that position
4002 // -- scan marked objects for oops
4003 // -- CAS-mark target, and if successful:
4004 // . if target oop is above global finger (volatile read)
4005 // nothing to do
4006 // . if target oop is in chunk and above local finger
4007 // then nothing to do
4008 // . else push on work-queue
4009 // -- Deal with possible overflow issues:
4010 // . local work-queue overflow causes stuff to be pushed on
4011 // global (common) overflow queue
4012 // . always first empty local work queue
4013 // . then get a batch of oops from global work queue if any
4014 // . then do work stealing
4015 // -- When all tasks claimed (both spaces)
4016 // and local work queue empty,
4017 // then in a loop do:
4018 // . check global overflow stack; steal a batch of oops and trace
4019 // . try to steal from other threads oif GOS is empty
4020 // . if neither is available, offer termination
4021 // -- Terminate and return result
4022 //
4023 void CMSConcMarkingTask::work(uint worker_id) {
4024 elapsedTimer _timer;
4025 ResourceMark rm;
4026 HandleMark hm;
4027
4028 DEBUG_ONLY(_collector->verify_overflow_empty();)
4029
4030 // Before we begin work, our work queue should be empty
4031 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4032 // Scan the bitmap covering _cms_space, tracing through grey objects.
4033 _timer.start();
4034 do_scan_and_mark(worker_id, _cms_space);
4035 _timer.stop();
4036 if (PrintCMSStatistics != 0) {
4037 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4038 worker_id, _timer.seconds());
4039 // XXX: need xxx/xxx type of notation, two timers
4040 }
4041
4042 // ... do work stealing
4043 _timer.reset();
4044 _timer.start();
4045 do_work_steal(worker_id);
4046 _timer.stop();
4047 if (PrintCMSStatistics != 0) {
4048 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4049 worker_id, _timer.seconds());
4050 // XXX: need xxx/xxx type of notation, two timers
4051 }
4052 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4053 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4054 // Note that under the current task protocol, the
4055 // following assertion is true even of the spaces
4056 // expanded since the completion of the concurrent
4057 // marking. XXX This will likely change under a strict
4058 // ABORT semantics.
4059 // After perm removal the comparison was changed to
4060 // greater than or equal to from strictly greater than.
4061 // Before perm removal the highest address sweep would
4062 // have been at the end of perm gen but now is at the
4063 // end of the tenured gen.
4064 assert(_global_finger >= _cms_space->end(),
4065 "All tasks have been completed");
4066 DEBUG_ONLY(_collector->verify_overflow_empty();)
4067 }
4068
4069 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4070 HeapWord* read = _global_finger;
4071 HeapWord* cur = read;
4072 while (f > read) {
4073 cur = read;
4074 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4075 if (cur == read) {
4076 // our cas succeeded
4077 assert(_global_finger >= f, "protocol consistency");
4078 break;
4079 }
4080 }
4081 }
4082
4083 // This is really inefficient, and should be redone by
4084 // using (not yet available) block-read and -write interfaces to the
4085 // stack and the work_queue. XXX FIX ME !!!
4086 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4087 OopTaskQueue* work_q) {
4088 // Fast lock-free check
4089 if (ovflw_stk->length() == 0) {
4090 return false;
4091 }
4092 assert(work_q->size() == 0, "Shouldn't steal");
4093 MutexLockerEx ml(ovflw_stk->par_lock(),
4094 Mutex::_no_safepoint_check_flag);
4095 // Grab up to 1/4 the size of the work queue
4096 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4097 (size_t)ParGCDesiredObjsFromOverflowList);
4098 num = MIN2(num, ovflw_stk->length());
4099 for (int i = (int) num; i > 0; i--) {
4100 oop cur = ovflw_stk->pop();
4101 assert(cur != NULL, "Counted wrong?");
4102 work_q->push(cur);
4103 }
4104 return num > 0;
4105 }
4106
4107 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4108 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4109 int n_tasks = pst->n_tasks();
4110 // We allow that there may be no tasks to do here because
4111 // we are restarting after a stack overflow.
4112 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4113 uint nth_task = 0;
4114
4115 HeapWord* aligned_start = sp->bottom();
4116 if (sp->used_region().contains(_restart_addr)) {
4117 // Align down to a card boundary for the start of 0th task
4118 // for this space.
4119 aligned_start =
4120 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4121 CardTableModRefBS::card_size);
4122 }
4123
4124 size_t chunk_size = sp->marking_task_size();
4125 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4126 // Having claimed the nth task in this space,
4127 // compute the chunk that it corresponds to:
4128 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4129 aligned_start + (nth_task+1)*chunk_size);
4130 // Try and bump the global finger via a CAS;
4131 // note that we need to do the global finger bump
4132 // _before_ taking the intersection below, because
4133 // the task corresponding to that region will be
4134 // deemed done even if the used_region() expands
4135 // because of allocation -- as it almost certainly will
4136 // during start-up while the threads yield in the
4137 // closure below.
4138 HeapWord* finger = span.end();
4139 bump_global_finger(finger); // atomically
4140 // There are null tasks here corresponding to chunks
4141 // beyond the "top" address of the space.
4142 span = span.intersection(sp->used_region());
4143 if (!span.is_empty()) { // Non-null task
4144 HeapWord* prev_obj;
4145 assert(!span.contains(_restart_addr) || nth_task == 0,
4146 "Inconsistency");
4147 if (nth_task == 0) {
4148 // For the 0th task, we'll not need to compute a block_start.
4149 if (span.contains(_restart_addr)) {
4150 // In the case of a restart because of stack overflow,
4151 // we might additionally skip a chunk prefix.
4152 prev_obj = _restart_addr;
4153 } else {
4154 prev_obj = span.start();
4155 }
4156 } else {
4157 // We want to skip the first object because
4158 // the protocol is to scan any object in its entirety
4159 // that _starts_ in this span; a fortiori, any
4160 // object starting in an earlier span is scanned
4161 // as part of an earlier claimed task.
4162 // Below we use the "careful" version of block_start
4163 // so we do not try to navigate uninitialized objects.
4164 prev_obj = sp->block_start_careful(span.start());
4165 // Below we use a variant of block_size that uses the
4166 // Printezis bits to avoid waiting for allocated
4167 // objects to become initialized/parsable.
4168 while (prev_obj < span.start()) {
4169 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4170 if (sz > 0) {
4171 prev_obj += sz;
4172 } else {
4173 // In this case we may end up doing a bit of redundant
4174 // scanning, but that appears unavoidable, short of
4175 // locking the free list locks; see bug 6324141.
4176 break;
4177 }
4178 }
4179 }
4180 if (prev_obj < span.end()) {
4181 MemRegion my_span = MemRegion(prev_obj, span.end());
4182 // Do the marking work within a non-empty span --
4183 // the last argument to the constructor indicates whether the
4184 // iteration should be incremental with periodic yields.
4185 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4186 &_collector->_markBitMap,
4187 work_queue(i),
4188 &_collector->_markStack,
4189 _asynch);
4190 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4191 } // else nothing to do for this task
4192 } // else nothing to do for this task
4193 }
4194 // We'd be tempted to assert here that since there are no
4195 // more tasks left to claim in this space, the global_finger
4196 // must exceed space->top() and a fortiori space->end(). However,
4197 // that would not quite be correct because the bumping of
4198 // global_finger occurs strictly after the claiming of a task,
4199 // so by the time we reach here the global finger may not yet
4200 // have been bumped up by the thread that claimed the last
4201 // task.
4202 pst->all_tasks_completed();
4203 }
4204
4205 class Par_ConcMarkingClosure: public CMSOopClosure {
4206 private:
4207 CMSCollector* _collector;
4208 CMSConcMarkingTask* _task;
4209 MemRegion _span;
4210 CMSBitMap* _bit_map;
4211 CMSMarkStack* _overflow_stack;
4212 OopTaskQueue* _work_queue;
4213 protected:
4214 DO_OOP_WORK_DEFN
4215 public:
4216 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4217 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4218 CMSOopClosure(collector->ref_processor()),
4219 _collector(collector),
4220 _task(task),
4221 _span(collector->_span),
4222 _work_queue(work_queue),
4223 _bit_map(bit_map),
4224 _overflow_stack(overflow_stack)
4225 { }
4226 virtual void do_oop(oop* p);
4227 virtual void do_oop(narrowOop* p);
4228
4229 void trim_queue(size_t max);
4230 void handle_stack_overflow(HeapWord* lost);
4231 void do_yield_check() {
4232 if (_task->should_yield()) {
4233 _task->yield();
4234 }
4235 }
4236 };
4237
4238 // Grey object scanning during work stealing phase --
4239 // the salient assumption here is that any references
4240 // that are in these stolen objects being scanned must
4241 // already have been initialized (else they would not have
4242 // been published), so we do not need to check for
4243 // uninitialized objects before pushing here.
4244 void Par_ConcMarkingClosure::do_oop(oop obj) {
4245 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4246 HeapWord* addr = (HeapWord*)obj;
4247 // Check if oop points into the CMS generation
4248 // and is not marked
4249 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4250 // a white object ...
4251 // If we manage to "claim" the object, by being the
4252 // first thread to mark it, then we push it on our
4253 // marking stack
4254 if (_bit_map->par_mark(addr)) { // ... now grey
4255 // push on work queue (grey set)
4256 bool simulate_overflow = false;
4257 NOT_PRODUCT(
4258 if (CMSMarkStackOverflowALot &&
4259 _collector->simulate_overflow()) {
4260 // simulate a stack overflow
4261 simulate_overflow = true;
4262 }
4263 )
4264 if (simulate_overflow ||
4265 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4266 // stack overflow
4267 if (PrintCMSStatistics != 0) {
4268 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4269 SIZE_FORMAT, _overflow_stack->capacity());
4270 }
4271 // We cannot assert that the overflow stack is full because
4272 // it may have been emptied since.
4273 assert(simulate_overflow ||
4274 _work_queue->size() == _work_queue->max_elems(),
4275 "Else push should have succeeded");
4276 handle_stack_overflow(addr);
4277 }
4278 } // Else, some other thread got there first
4279 do_yield_check();
4280 }
4281 }
4282
4283 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4284 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4285
4286 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4287 while (_work_queue->size() > max) {
4288 oop new_oop;
4289 if (_work_queue->pop_local(new_oop)) {
4290 assert(new_oop->is_oop(), "Should be an oop");
4291 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4292 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4293 new_oop->oop_iterate(this); // do_oop() above
4294 do_yield_check();
4295 }
4296 }
4297 }
4298
4299 // Upon stack overflow, we discard (part of) the stack,
4300 // remembering the least address amongst those discarded
4301 // in CMSCollector's _restart_address.
4302 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4303 // We need to do this under a mutex to prevent other
4304 // workers from interfering with the work done below.
4305 MutexLockerEx ml(_overflow_stack->par_lock(),
4306 Mutex::_no_safepoint_check_flag);
4307 // Remember the least grey address discarded
4308 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4309 _collector->lower_restart_addr(ra);
4310 _overflow_stack->reset(); // discard stack contents
4311 _overflow_stack->expand(); // expand the stack if possible
4312 }
4313
4314
4315 void CMSConcMarkingTask::do_work_steal(int i) {
4316 OopTaskQueue* work_q = work_queue(i);
4317 oop obj_to_scan;
4318 CMSBitMap* bm = &(_collector->_markBitMap);
4319 CMSMarkStack* ovflw = &(_collector->_markStack);
4320 int* seed = _collector->hash_seed(i);
4321 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4322 while (true) {
4323 cl.trim_queue(0);
4324 assert(work_q->size() == 0, "Should have been emptied above");
4325 if (get_work_from_overflow_stack(ovflw, work_q)) {
4326 // Can't assert below because the work obtained from the
4327 // overflow stack may already have been stolen from us.
4328 // assert(work_q->size() > 0, "Work from overflow stack");
4329 continue;
4330 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4331 assert(obj_to_scan->is_oop(), "Should be an oop");
4332 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4333 obj_to_scan->oop_iterate(&cl);
4334 } else if (terminator()->offer_termination(&_term_term)) {
4335 assert(work_q->size() == 0, "Impossible!");
4336 break;
4337 } else if (yielding() || should_yield()) {
4338 yield();
4339 }
4340 }
4341 }
4342
4343 // This is run by the CMS (coordinator) thread.
4344 void CMSConcMarkingTask::coordinator_yield() {
4345 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4346 "CMS thread should hold CMS token");
4347 // First give up the locks, then yield, then re-lock
4348 // We should probably use a constructor/destructor idiom to
4349 // do this unlock/lock or modify the MutexUnlocker class to
4350 // serve our purpose. XXX
4351 assert_lock_strong(_bit_map_lock);
4352 _bit_map_lock->unlock();
4353 ConcurrentMarkSweepThread::desynchronize(true);
4354 ConcurrentMarkSweepThread::acknowledge_yield_request();
4355 _collector->stopTimer();
4356 if (PrintCMSStatistics != 0) {
4357 _collector->incrementYields();
4358 }
4359 _collector->icms_wait();
4360
4361 // It is possible for whichever thread initiated the yield request
4362 // not to get a chance to wake up and take the bitmap lock between
4363 // this thread releasing it and reacquiring it. So, while the
4364 // should_yield() flag is on, let's sleep for a bit to give the
4365 // other thread a chance to wake up. The limit imposed on the number
4366 // of iterations is defensive, to avoid any unforseen circumstances
4367 // putting us into an infinite loop. Since it's always been this
4368 // (coordinator_yield()) method that was observed to cause the
4369 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4370 // which is by default non-zero. For the other seven methods that
4371 // also perform the yield operation, as are using a different
4372 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4373 // can enable the sleeping for those methods too, if necessary.
4374 // See 6442774.
4375 //
4376 // We really need to reconsider the synchronization between the GC
4377 // thread and the yield-requesting threads in the future and we
4378 // should really use wait/notify, which is the recommended
4379 // way of doing this type of interaction. Additionally, we should
4380 // consolidate the eight methods that do the yield operation and they
4381 // are almost identical into one for better maintainability and
4382 // readability. See 6445193.
4383 //
4384 // Tony 2006.06.29
4385 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4386 ConcurrentMarkSweepThread::should_yield() &&
4387 !CMSCollector::foregroundGCIsActive(); ++i) {
4388 os::sleep(Thread::current(), 1, false);
4389 ConcurrentMarkSweepThread::acknowledge_yield_request();
4390 }
4391
4392 ConcurrentMarkSweepThread::synchronize(true);
4393 _bit_map_lock->lock_without_safepoint_check();
4394 _collector->startTimer();
4395 }
4396
4397 bool CMSCollector::do_marking_mt(bool asynch) {
4398 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4399 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4400 conc_workers()->total_workers(),
4401 conc_workers()->active_workers(),
4402 Threads::number_of_non_daemon_threads());
4403 conc_workers()->set_active_workers(num_workers);
4404
4405 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4406
4407 CMSConcMarkingTask tsk(this,
4408 cms_space,
4409 asynch,
4410 conc_workers(),
4411 task_queues());
4412
4413 // Since the actual number of workers we get may be different
4414 // from the number we requested above, do we need to do anything different
4415 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4416 // class?? XXX
4417 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4418
4419 // Refs discovery is already non-atomic.
4420 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4421 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4422 conc_workers()->start_task(&tsk);
4423 while (tsk.yielded()) {
4424 tsk.coordinator_yield();
4425 conc_workers()->continue_task(&tsk);
4426 }
4427 // If the task was aborted, _restart_addr will be non-NULL
4428 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4429 while (_restart_addr != NULL) {
4430 // XXX For now we do not make use of ABORTED state and have not
4431 // yet implemented the right abort semantics (even in the original
4432 // single-threaded CMS case). That needs some more investigation
4433 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4434 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4435 // If _restart_addr is non-NULL, a marking stack overflow
4436 // occurred; we need to do a fresh marking iteration from the
4437 // indicated restart address.
4438 if (_foregroundGCIsActive && asynch) {
4439 // We may be running into repeated stack overflows, having
4440 // reached the limit of the stack size, while making very
4441 // slow forward progress. It may be best to bail out and
4442 // let the foreground collector do its job.
4443 // Clear _restart_addr, so that foreground GC
4444 // works from scratch. This avoids the headache of
4445 // a "rescan" which would otherwise be needed because
4446 // of the dirty mod union table & card table.
4447 _restart_addr = NULL;
4448 return false;
4449 }
4450 // Adjust the task to restart from _restart_addr
4451 tsk.reset(_restart_addr);
4452 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4453 _restart_addr);
4454 _restart_addr = NULL;
4455 // Get the workers going again
4456 conc_workers()->start_task(&tsk);
4457 while (tsk.yielded()) {
4458 tsk.coordinator_yield();
4459 conc_workers()->continue_task(&tsk);
4460 }
4461 }
4462 assert(tsk.completed(), "Inconsistency");
4463 assert(tsk.result() == true, "Inconsistency");
4464 return true;
4465 }
4466
4467 bool CMSCollector::do_marking_st(bool asynch) {
4468 ResourceMark rm;
4469 HandleMark hm;
4470
4471 // Temporarily make refs discovery single threaded (non-MT)
4472 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4473 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4474 &_markStack, CMSYield && asynch);
4475 // the last argument to iterate indicates whether the iteration
4476 // should be incremental with periodic yields.
4477 _markBitMap.iterate(&markFromRootsClosure);
4478 // If _restart_addr is non-NULL, a marking stack overflow
4479 // occurred; we need to do a fresh iteration from the
4480 // indicated restart address.
4481 while (_restart_addr != NULL) {
4482 if (_foregroundGCIsActive && asynch) {
4483 // We may be running into repeated stack overflows, having
4484 // reached the limit of the stack size, while making very
4485 // slow forward progress. It may be best to bail out and
4486 // let the foreground collector do its job.
4487 // Clear _restart_addr, so that foreground GC
4488 // works from scratch. This avoids the headache of
4489 // a "rescan" which would otherwise be needed because
4490 // of the dirty mod union table & card table.
4491 _restart_addr = NULL;
4492 return false; // indicating failure to complete marking
4493 }
4494 // Deal with stack overflow:
4495 // we restart marking from _restart_addr
4496 HeapWord* ra = _restart_addr;
4497 markFromRootsClosure.reset(ra);
4498 _restart_addr = NULL;
4499 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4500 }
4501 return true;
4502 }
4503
4504 void CMSCollector::preclean() {
4505 check_correct_thread_executing();
4506 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4507 verify_work_stacks_empty();
4508 verify_overflow_empty();
4509 _abort_preclean = false;
4510 if (CMSPrecleaningEnabled) {
4511 if (!CMSEdenChunksRecordAlways) {
4512 _eden_chunk_index = 0;
4513 }
4514 size_t used = get_eden_used();
4515 size_t capacity = get_eden_capacity();
4516 // Don't start sampling unless we will get sufficiently
4517 // many samples.
4518 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4519 * CMSScheduleRemarkEdenPenetration)) {
4520 _start_sampling = true;
4521 } else {
4522 _start_sampling = false;
4523 }
4524 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4525 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4526 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4527 }
4528 CMSTokenSync x(true); // is cms thread
4529 if (CMSPrecleaningEnabled) {
4530 sample_eden();
4531 _collectorState = AbortablePreclean;
4532 } else {
4533 _collectorState = FinalMarking;
4534 }
4535 verify_work_stacks_empty();
4536 verify_overflow_empty();
4537 }
4538
4539 // Try and schedule the remark such that young gen
4540 // occupancy is CMSScheduleRemarkEdenPenetration %.
4541 void CMSCollector::abortable_preclean() {
4542 check_correct_thread_executing();
4543 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4544 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4545
4546 // If Eden's current occupancy is below this threshold,
4547 // immediately schedule the remark; else preclean
4548 // past the next scavenge in an effort to
4549 // schedule the pause as described above. By choosing
4550 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4551 // we will never do an actual abortable preclean cycle.
4552 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4553 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4554 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4555 // We need more smarts in the abortable preclean
4556 // loop below to deal with cases where allocation
4557 // in young gen is very very slow, and our precleaning
4558 // is running a losing race against a horde of
4559 // mutators intent on flooding us with CMS updates
4560 // (dirty cards).
4561 // One, admittedly dumb, strategy is to give up
4562 // after a certain number of abortable precleaning loops
4563 // or after a certain maximum time. We want to make
4564 // this smarter in the next iteration.
4565 // XXX FIX ME!!! YSR
4566 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4567 while (!(should_abort_preclean() ||
4568 ConcurrentMarkSweepThread::should_terminate())) {
4569 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4570 cumworkdone += workdone;
4571 loops++;
4572 // Voluntarily terminate abortable preclean phase if we have
4573 // been at it for too long.
4574 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4575 loops >= CMSMaxAbortablePrecleanLoops) {
4576 if (PrintGCDetails) {
4577 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4578 }
4579 break;
4580 }
4581 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4582 if (PrintGCDetails) {
4583 gclog_or_tty->print(" CMS: abort preclean due to time ");
4584 }
4585 break;
4586 }
4587 // If we are doing little work each iteration, we should
4588 // take a short break.
4589 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4590 // Sleep for some time, waiting for work to accumulate
4591 stopTimer();
4592 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4593 startTimer();
4594 waited++;
4595 }
4596 }
4597 if (PrintCMSStatistics > 0) {
4598 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
4599 loops, waited, cumworkdone);
4600 }
4601 }
4602 CMSTokenSync x(true); // is cms thread
4603 if (_collectorState != Idling) {
4604 assert(_collectorState == AbortablePreclean,
4605 "Spontaneous state transition?");
4606 _collectorState = FinalMarking;
4607 } // Else, a foreground collection completed this CMS cycle.
4608 return;
4609 }
4610
4611 // Respond to an Eden sampling opportunity
4612 void CMSCollector::sample_eden() {
4613 // Make sure a young gc cannot sneak in between our
4614 // reading and recording of a sample.
4615 assert(Thread::current()->is_ConcurrentGC_thread(),
4616 "Only the cms thread may collect Eden samples");
4617 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4618 "Should collect samples while holding CMS token");
4619 if (!_start_sampling) {
4620 return;
4621 }
4622 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4623 // is populated by the young generation.
4624 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4625 if (_eden_chunk_index < _eden_chunk_capacity) {
4626 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4627 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4628 "Unexpected state of Eden");
4629 // We'd like to check that what we just sampled is an oop-start address;
4630 // however, we cannot do that here since the object may not yet have been
4631 // initialized. So we'll instead do the check when we _use_ this sample
4632 // later.
4633 if (_eden_chunk_index == 0 ||
4634 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4635 _eden_chunk_array[_eden_chunk_index-1])
4636 >= CMSSamplingGrain)) {
4637 _eden_chunk_index++; // commit sample
4638 }
4639 }
4640 }
4641 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4642 size_t used = get_eden_used();
4643 size_t capacity = get_eden_capacity();
4644 assert(used <= capacity, "Unexpected state of Eden");
4645 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4646 _abort_preclean = true;
4647 }
4648 }
4649 }
4650
4651
4652 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4653 assert(_collectorState == Precleaning ||
4654 _collectorState == AbortablePreclean, "incorrect state");
4655 ResourceMark rm;
4656 HandleMark hm;
4657
4658 // Precleaning is currently not MT but the reference processor
4659 // may be set for MT. Disable it temporarily here.
4660 ReferenceProcessor* rp = ref_processor();
4661 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4662
4663 // Do one pass of scrubbing the discovered reference lists
4664 // to remove any reference objects with strongly-reachable
4665 // referents.
4666 if (clean_refs) {
4667 CMSPrecleanRefsYieldClosure yield_cl(this);
4668 assert(rp->span().equals(_span), "Spans should be equal");
4669 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4670 &_markStack, true /* preclean */);
4671 CMSDrainMarkingStackClosure complete_trace(this,
4672 _span, &_markBitMap, &_markStack,
4673 &keep_alive, true /* preclean */);
4674
4675 // We don't want this step to interfere with a young
4676 // collection because we don't want to take CPU
4677 // or memory bandwidth away from the young GC threads
4678 // (which may be as many as there are CPUs).
4679 // Note that we don't need to protect ourselves from
4680 // interference with mutators because they can't
4681 // manipulate the discovered reference lists nor affect
4682 // the computed reachability of the referents, the
4683 // only properties manipulated by the precleaning
4684 // of these reference lists.
4685 stopTimer();
4686 CMSTokenSyncWithLocks x(true /* is cms thread */,
4687 bitMapLock());
4688 startTimer();
4689 sample_eden();
4690
4691 // The following will yield to allow foreground
4692 // collection to proceed promptly. XXX YSR:
4693 // The code in this method may need further
4694 // tweaking for better performance and some restructuring
4695 // for cleaner interfaces.
4696 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4697 rp->preclean_discovered_references(
4698 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4699 gc_timer);
4700 }
4701
4702 if (clean_survivor) { // preclean the active survivor space(s)
4703 assert(_young_gen->kind() == Generation::DefNew ||
4704 _young_gen->kind() == Generation::ParNew ||
4705 _young_gen->kind() == Generation::ASParNew,
4706 "incorrect type for cast");
4707 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4708 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4709 &_markBitMap, &_modUnionTable,
4710 &_markStack, true /* precleaning phase */);
4711 stopTimer();
4712 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4713 bitMapLock());
4714 startTimer();
4715 unsigned int before_count =
4716 GenCollectedHeap::heap()->total_collections();
4717 SurvivorSpacePrecleanClosure
4718 sss_cl(this, _span, &_markBitMap, &_markStack,
4719 &pam_cl, before_count, CMSYield);
4720 dng->from()->object_iterate_careful(&sss_cl);
4721 dng->to()->object_iterate_careful(&sss_cl);
4722 }
4723 MarkRefsIntoAndScanClosure
4724 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4725 &_markStack, this, CMSYield,
4726 true /* precleaning phase */);
4727 // CAUTION: The following closure has persistent state that may need to
4728 // be reset upon a decrease in the sequence of addresses it
4729 // processes.
4730 ScanMarkedObjectsAgainCarefullyClosure
4731 smoac_cl(this, _span,
4732 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4733
4734 // Preclean dirty cards in ModUnionTable and CardTable using
4735 // appropriate convergence criterion;
4736 // repeat CMSPrecleanIter times unless we find that
4737 // we are losing.
4738 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4739 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4740 "Bad convergence multiplier");
4741 assert(CMSPrecleanThreshold >= 100,
4742 "Unreasonably low CMSPrecleanThreshold");
4743
4744 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4745 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4746 numIter < CMSPrecleanIter;
4747 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4748 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4749 if (Verbose && PrintGCDetails) {
4750 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
4751 }
4752 // Either there are very few dirty cards, so re-mark
4753 // pause will be small anyway, or our pre-cleaning isn't
4754 // that much faster than the rate at which cards are being
4755 // dirtied, so we might as well stop and re-mark since
4756 // precleaning won't improve our re-mark time by much.
4757 if (curNumCards <= CMSPrecleanThreshold ||
4758 (numIter > 0 &&
4759 (curNumCards * CMSPrecleanDenominator >
4760 lastNumCards * CMSPrecleanNumerator))) {
4761 numIter++;
4762 cumNumCards += curNumCards;
4763 break;
4764 }
4765 }
4766
4767 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4768
4769 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4770 cumNumCards += curNumCards;
4771 if (PrintGCDetails && PrintCMSStatistics != 0) {
4772 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4773 curNumCards, cumNumCards, numIter);
4774 }
4775 return cumNumCards; // as a measure of useful work done
4776 }
4777
4778 // PRECLEANING NOTES:
4779 // Precleaning involves:
4780 // . reading the bits of the modUnionTable and clearing the set bits.
4781 // . For the cards corresponding to the set bits, we scan the
4782 // objects on those cards. This means we need the free_list_lock
4783 // so that we can safely iterate over the CMS space when scanning
4784 // for oops.
4785 // . When we scan the objects, we'll be both reading and setting
4786 // marks in the marking bit map, so we'll need the marking bit map.
4787 // . For protecting _collector_state transitions, we take the CGC_lock.
4788 // Note that any races in the reading of of card table entries by the
4789 // CMS thread on the one hand and the clearing of those entries by the
4790 // VM thread or the setting of those entries by the mutator threads on the
4791 // other are quite benign. However, for efficiency it makes sense to keep
4792 // the VM thread from racing with the CMS thread while the latter is
4793 // dirty card info to the modUnionTable. We therefore also use the
4794 // CGC_lock to protect the reading of the card table and the mod union
4795 // table by the CM thread.
4796 // . We run concurrently with mutator updates, so scanning
4797 // needs to be done carefully -- we should not try to scan
4798 // potentially uninitialized objects.
4799 //
4800 // Locking strategy: While holding the CGC_lock, we scan over and
4801 // reset a maximal dirty range of the mod union / card tables, then lock
4802 // the free_list_lock and bitmap lock to do a full marking, then
4803 // release these locks; and repeat the cycle. This allows for a
4804 // certain amount of fairness in the sharing of these locks between
4805 // the CMS collector on the one hand, and the VM thread and the
4806 // mutators on the other.
4807
4808 // NOTE: preclean_mod_union_table() and preclean_card_table()
4809 // further below are largely identical; if you need to modify
4810 // one of these methods, please check the other method too.
4811
4812 size_t CMSCollector::preclean_mod_union_table(
4813 ConcurrentMarkSweepGeneration* gen,
4814 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4815 verify_work_stacks_empty();
4816 verify_overflow_empty();
4817
4818 // strategy: starting with the first card, accumulate contiguous
4819 // ranges of dirty cards; clear these cards, then scan the region
4820 // covered by these cards.
4821
4822 // Since all of the MUT is committed ahead, we can just use
4823 // that, in case the generations expand while we are precleaning.
4824 // It might also be fine to just use the committed part of the
4825 // generation, but we might potentially miss cards when the
4826 // generation is rapidly expanding while we are in the midst
4827 // of precleaning.
4828 HeapWord* startAddr = gen->reserved().start();
4829 HeapWord* endAddr = gen->reserved().end();
4830
4831 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4832
4833 size_t numDirtyCards, cumNumDirtyCards;
4834 HeapWord *nextAddr, *lastAddr;
4835 for (cumNumDirtyCards = numDirtyCards = 0,
4836 nextAddr = lastAddr = startAddr;
4837 nextAddr < endAddr;
4838 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4839
4840 ResourceMark rm;
4841 HandleMark hm;
4842
4843 MemRegion dirtyRegion;
4844 {
4845 stopTimer();
4846 // Potential yield point
4847 CMSTokenSync ts(true);
4848 startTimer();
4849 sample_eden();
4850 // Get dirty region starting at nextOffset (inclusive),
4851 // simultaneously clearing it.
4852 dirtyRegion =
4853 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4854 assert(dirtyRegion.start() >= nextAddr,
4855 "returned region inconsistent?");
4856 }
4857 // Remember where the next search should begin.
4858 // The returned region (if non-empty) is a right open interval,
4859 // so lastOffset is obtained from the right end of that
4860 // interval.
4861 lastAddr = dirtyRegion.end();
4862 // Should do something more transparent and less hacky XXX
4863 numDirtyCards =
4864 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4865
4866 // We'll scan the cards in the dirty region (with periodic
4867 // yields for foreground GC as needed).
4868 if (!dirtyRegion.is_empty()) {
4869 assert(numDirtyCards > 0, "consistency check");
4870 HeapWord* stop_point = NULL;
4871 stopTimer();
4872 // Potential yield point
4873 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4874 bitMapLock());
4875 startTimer();
4876 {
4877 verify_work_stacks_empty();
4878 verify_overflow_empty();
4879 sample_eden();
4880 stop_point =
4881 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4882 }
4883 if (stop_point != NULL) {
4884 // The careful iteration stopped early either because it found an
4885 // uninitialized object, or because we were in the midst of an
4886 // "abortable preclean", which should now be aborted. Redirty
4887 // the bits corresponding to the partially-scanned or unscanned
4888 // cards. We'll either restart at the next block boundary or
4889 // abort the preclean.
4890 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4891 "Should only be AbortablePreclean.");
4892 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4893 if (should_abort_preclean()) {
4894 break; // out of preclean loop
4895 } else {
4896 // Compute the next address at which preclean should pick up;
4897 // might need bitMapLock in order to read P-bits.
4898 lastAddr = next_card_start_after_block(stop_point);
4899 }
4900 }
4901 } else {
4902 assert(lastAddr == endAddr, "consistency check");
4903 assert(numDirtyCards == 0, "consistency check");
4904 break;
4905 }
4906 }
4907 verify_work_stacks_empty();
4908 verify_overflow_empty();
4909 return cumNumDirtyCards;
4910 }
4911
4912 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4913 // below are largely identical; if you need to modify
4914 // one of these methods, please check the other method too.
4915
4916 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4917 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4918 // strategy: it's similar to precleamModUnionTable above, in that
4919 // we accumulate contiguous ranges of dirty cards, mark these cards
4920 // precleaned, then scan the region covered by these cards.
4921 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4922 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4923
4924 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4925
4926 size_t numDirtyCards, cumNumDirtyCards;
4927 HeapWord *lastAddr, *nextAddr;
4928
4929 for (cumNumDirtyCards = numDirtyCards = 0,
4930 nextAddr = lastAddr = startAddr;
4931 nextAddr < endAddr;
4932 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4933
4934 ResourceMark rm;
4935 HandleMark hm;
4936
4937 MemRegion dirtyRegion;
4938 {
4939 // See comments in "Precleaning notes" above on why we
4940 // do this locking. XXX Could the locking overheads be
4941 // too high when dirty cards are sparse? [I don't think so.]
4942 stopTimer();
4943 CMSTokenSync x(true); // is cms thread
4944 startTimer();
4945 sample_eden();
4946 // Get and clear dirty region from card table
4947 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4948 MemRegion(nextAddr, endAddr),
4949 true,
4950 CardTableModRefBS::precleaned_card_val());
4951
4952 assert(dirtyRegion.start() >= nextAddr,
4953 "returned region inconsistent?");
4954 }
4955 lastAddr = dirtyRegion.end();
4956 numDirtyCards =
4957 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4958
4959 if (!dirtyRegion.is_empty()) {
4960 stopTimer();
4961 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4962 startTimer();
4963 sample_eden();
4964 verify_work_stacks_empty();
4965 verify_overflow_empty();
4966 HeapWord* stop_point =
4967 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4968 if (stop_point != NULL) {
4969 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4970 "Should only be AbortablePreclean.");
4971 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4972 if (should_abort_preclean()) {
4973 break; // out of preclean loop
4974 } else {
4975 // Compute the next address at which preclean should pick up.
4976 lastAddr = next_card_start_after_block(stop_point);
4977 }
4978 }
4979 } else {
4980 break;
4981 }
4982 }
4983 verify_work_stacks_empty();
4984 verify_overflow_empty();
4985 return cumNumDirtyCards;
4986 }
4987
4988 class PrecleanKlassClosure : public KlassClosure {
4989 CMKlassClosure _cm_klass_closure;
4990 public:
4991 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4992 void do_klass(Klass* k) {
4993 if (k->has_accumulated_modified_oops()) {
4994 k->clear_accumulated_modified_oops();
4995
4996 _cm_klass_closure.do_klass(k);
4997 }
4998 }
4999 };
5000
5001 // The freelist lock is needed to prevent asserts, is it really needed?
5002 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
5003
5004 cl->set_freelistLock(freelistLock);
5005
5006 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
5007
5008 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
5009 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
5010 PrecleanKlassClosure preclean_klass_closure(cl);
5011 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
5012
5013 verify_work_stacks_empty();
5014 verify_overflow_empty();
5015 }
5016
5017 void CMSCollector::checkpointRootsFinal(bool asynch,
5018 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5019 assert(_collectorState == FinalMarking, "incorrect state transition?");
5020 check_correct_thread_executing();
5021 // world is stopped at this checkpoint
5022 assert(SafepointSynchronize::is_at_safepoint(),
5023 "world should be stopped");
5024 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5025
5026 verify_work_stacks_empty();
5027 verify_overflow_empty();
5028
5029 SpecializationStats::clear();
5030 if (PrintGCDetails) {
5031 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5032 _young_gen->used() / K,
5033 _young_gen->capacity() / K);
5034 }
5035 if (asynch) {
5036 if (CMSScavengeBeforeRemark) {
5037 GenCollectedHeap* gch = GenCollectedHeap::heap();
5038 // Temporarily set flag to false, GCH->do_collection will
5039 // expect it to be false and set to true
5040 FlagSetting fl(gch->_is_gc_active, false);
5041 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5042 PrintGCDetails && Verbose, true, _gc_timer_cm);)
5043 int level = _cmsGen->level() - 1;
5044 if (level >= 0) {
5045 gch->do_collection(true, // full (i.e. force, see below)
5046 false, // !clear_all_soft_refs
5047 0, // size
5048 false, // is_tlab
5049 level // max_level
5050 );
5051 }
5052 }
5053 FreelistLocker x(this);
5054 MutexLockerEx y(bitMapLock(),
5055 Mutex::_no_safepoint_check_flag);
5056 assert(!init_mark_was_synchronous, "but that's impossible!");
5057 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5058 } else {
5059 // already have all the locks
5060 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5061 init_mark_was_synchronous);
5062 }
5063 verify_work_stacks_empty();
5064 verify_overflow_empty();
5065 SpecializationStats::print();
5066 }
5067
5068 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5069 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5070
5071 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
5072
5073 assert(haveFreelistLocks(), "must have free list locks");
5074 assert_lock_strong(bitMapLock());
5075
5076 if (UseAdaptiveSizePolicy) {
5077 size_policy()->checkpoint_roots_final_begin();
5078 }
5079
5080 ResourceMark rm;
5081 HandleMark hm;
5082
5083 GenCollectedHeap* gch = GenCollectedHeap::heap();
5084
5085 if (should_unload_classes()) {
5086 CodeCache::gc_prologue();
5087 }
5088 assert(haveFreelistLocks(), "must have free list locks");
5089 assert_lock_strong(bitMapLock());
5090
5091 if (!init_mark_was_synchronous) {
5092 // We might assume that we need not fill TLAB's when
5093 // CMSScavengeBeforeRemark is set, because we may have just done
5094 // a scavenge which would have filled all TLAB's -- and besides
5095 // Eden would be empty. This however may not always be the case --
5096 // for instance although we asked for a scavenge, it may not have
5097 // happened because of a JNI critical section. We probably need
5098 // a policy for deciding whether we can in that case wait until
5099 // the critical section releases and then do the remark following
5100 // the scavenge, and skip it here. In the absence of that policy,
5101 // or of an indication of whether the scavenge did indeed occur,
5102 // we cannot rely on TLAB's having been filled and must do
5103 // so here just in case a scavenge did not happen.
5104 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5105 // Update the saved marks which may affect the root scans.
5106 gch->save_marks();
5107
5108 if (CMSPrintEdenSurvivorChunks) {
5109 print_eden_and_survivor_chunk_arrays();
5110 }
5111
5112 {
5113 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5114
5115 // Note on the role of the mod union table:
5116 // Since the marker in "markFromRoots" marks concurrently with
5117 // mutators, it is possible for some reachable objects not to have been
5118 // scanned. For instance, an only reference to an object A was
5119 // placed in object B after the marker scanned B. Unless B is rescanned,
5120 // A would be collected. Such updates to references in marked objects
5121 // are detected via the mod union table which is the set of all cards
5122 // dirtied since the first checkpoint in this GC cycle and prior to
5123 // the most recent young generation GC, minus those cleaned up by the
5124 // concurrent precleaning.
5125 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5126 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5127 do_remark_parallel();
5128 } else {
5129 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5130 _gc_timer_cm);
5131 do_remark_non_parallel();
5132 }
5133 }
5134 } else {
5135 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5136 // The initial mark was stop-world, so there's no rescanning to
5137 // do; go straight on to the next step below.
5138 }
5139 verify_work_stacks_empty();
5140 verify_overflow_empty();
5141
5142 {
5143 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5144 refProcessingWork(asynch, clear_all_soft_refs);
5145 }
5146 verify_work_stacks_empty();
5147 verify_overflow_empty();
5148
5149 if (should_unload_classes()) {
5150 CodeCache::gc_epilogue();
5151 }
5152 JvmtiExport::gc_epilogue();
5153
5154 // If we encountered any (marking stack / work queue) overflow
5155 // events during the current CMS cycle, take appropriate
5156 // remedial measures, where possible, so as to try and avoid
5157 // recurrence of that condition.
5158 assert(_markStack.isEmpty(), "No grey objects");
5159 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5160 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5161 if (ser_ovflw > 0) {
5162 if (PrintCMSStatistics != 0) {
5163 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5164 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5165 ", kac_preclean="SIZE_FORMAT")",
5166 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5167 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5168 }
5169 _markStack.expand();
5170 _ser_pmc_remark_ovflw = 0;
5171 _ser_pmc_preclean_ovflw = 0;
5172 _ser_kac_preclean_ovflw = 0;
5173 _ser_kac_ovflw = 0;
5174 }
5175 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5176 if (PrintCMSStatistics != 0) {
5177 gclog_or_tty->print_cr("Work queue overflow (benign) "
5178 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5179 _par_pmc_remark_ovflw, _par_kac_ovflw);
5180 }
5181 _par_pmc_remark_ovflw = 0;
5182 _par_kac_ovflw = 0;
5183 }
5184 if (PrintCMSStatistics != 0) {
5185 if (_markStack._hit_limit > 0) {
5186 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5187 _markStack._hit_limit);
5188 }
5189 if (_markStack._failed_double > 0) {
5190 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5191 " current capacity "SIZE_FORMAT,
5192 _markStack._failed_double,
5193 _markStack.capacity());
5194 }
5195 }
5196 _markStack._hit_limit = 0;
5197 _markStack._failed_double = 0;
5198
5199 if ((VerifyAfterGC || VerifyDuringGC) &&
5200 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5201 verify_after_remark();
5202 }
5203
5204 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5205
5206 // Change under the freelistLocks.
5207 _collectorState = Sweeping;
5208 // Call isAllClear() under bitMapLock
5209 assert(_modUnionTable.isAllClear(),
5210 "Should be clear by end of the final marking");
5211 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5212 "Should be clear by end of the final marking");
5213 if (UseAdaptiveSizePolicy) {
5214 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5215 }
5216 }
5217
5218 void CMSParInitialMarkTask::work(uint worker_id) {
5219 elapsedTimer _timer;
5220 ResourceMark rm;
5221 HandleMark hm;
5222
5223 // ---------- scan from roots --------------
5224 _timer.start();
5225 GenCollectedHeap* gch = GenCollectedHeap::heap();
5226 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5227 CMKlassClosure klass_closure(&par_mri_cl);
5228
5229 // ---------- young gen roots --------------
5230 {
5231 work_on_young_gen_roots(worker_id, &par_mri_cl);
5232 _timer.stop();
5233 if (PrintCMSStatistics != 0) {
5234 gclog_or_tty->print_cr(
5235 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5236 worker_id, _timer.seconds());
5237 }
5238 }
5239
5240 // ---------- remaining roots --------------
5241 _timer.reset();
5242 _timer.start();
5243 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5244 false, // yg was scanned above
5245 false, // this is parallel code
5246 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5247 &par_mri_cl,
5248 NULL,
5249 &klass_closure);
5250 assert(_collector->should_unload_classes()
5251 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5252 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5253 _timer.stop();
5254 if (PrintCMSStatistics != 0) {
5255 gclog_or_tty->print_cr(
5256 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5257 worker_id, _timer.seconds());
5258 }
5259 }
5260
5261 // Parallel remark task
5262 class CMSParRemarkTask: public CMSParMarkTask {
5263 CompactibleFreeListSpace* _cms_space;
5264
5265 // The per-thread work queues, available here for stealing.
5266 OopTaskQueueSet* _task_queues;
5267 ParallelTaskTerminator _term;
5268
5269 public:
5270 // A value of 0 passed to n_workers will cause the number of
5271 // workers to be taken from the active workers in the work gang.
5272 CMSParRemarkTask(CMSCollector* collector,
5273 CompactibleFreeListSpace* cms_space,
5274 int n_workers, FlexibleWorkGang* workers,
5275 OopTaskQueueSet* task_queues):
5276 CMSParMarkTask("Rescan roots and grey objects in parallel",
5277 collector, n_workers),
5278 _cms_space(cms_space),
5279 _task_queues(task_queues),
5280 _term(n_workers, task_queues) { }
5281
5282 OopTaskQueueSet* task_queues() { return _task_queues; }
5283
5284 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5285
5286 ParallelTaskTerminator* terminator() { return &_term; }
5287 int n_workers() { return _n_workers; }
5288
5289 void work(uint worker_id);
5290
5291 private:
5292 // ... of dirty cards in old space
5293 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5294 Par_MarkRefsIntoAndScanClosure* cl);
5295
5296 // ... work stealing for the above
5297 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5298 };
5299
5300 class RemarkKlassClosure : public KlassClosure {
5301 CMKlassClosure _cm_klass_closure;
5302 public:
5303 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5304 void do_klass(Klass* k) {
5305 // Check if we have modified any oops in the Klass during the concurrent marking.
5306 if (k->has_accumulated_modified_oops()) {
5307 k->clear_accumulated_modified_oops();
5308
5309 // We could have transfered the current modified marks to the accumulated marks,
5310 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5311 } else if (k->has_modified_oops()) {
5312 // Don't clear anything, this info is needed by the next young collection.
5313 } else {
5314 // No modified oops in the Klass.
5315 return;
5316 }
5317
5318 // The klass has modified fields, need to scan the klass.
5319 _cm_klass_closure.do_klass(k);
5320 }
5321 };
5322
5323 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5324 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5325 EdenSpace* eden_space = dng->eden();
5326 ContiguousSpace* from_space = dng->from();
5327 ContiguousSpace* to_space = dng->to();
5328
5329 HeapWord** eca = _collector->_eden_chunk_array;
5330 size_t ect = _collector->_eden_chunk_index;
5331 HeapWord** sca = _collector->_survivor_chunk_array;
5332 size_t sct = _collector->_survivor_chunk_index;
5333
5334 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5335 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5336
5337 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5338 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5339 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5340 }
5341
5342 // work_queue(i) is passed to the closure
5343 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5344 // also is passed to do_dirty_card_rescan_tasks() and to
5345 // do_work_steal() to select the i-th task_queue.
5346
5347 void CMSParRemarkTask::work(uint worker_id) {
5348 elapsedTimer _timer;
5349 ResourceMark rm;
5350 HandleMark hm;
5351
5352 // ---------- rescan from roots --------------
5353 _timer.start();
5354 GenCollectedHeap* gch = GenCollectedHeap::heap();
5355 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5356 _collector->_span, _collector->ref_processor(),
5357 &(_collector->_markBitMap),
5358 work_queue(worker_id));
5359
5360 // Rescan young gen roots first since these are likely
5361 // coarsely partitioned and may, on that account, constitute
5362 // the critical path; thus, it's best to start off that
5363 // work first.
5364 // ---------- young gen roots --------------
5365 {
5366 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5367 _timer.stop();
5368 if (PrintCMSStatistics != 0) {
5369 gclog_or_tty->print_cr(
5370 "Finished young gen rescan work in %dth thread: %3.3f sec",
5371 worker_id, _timer.seconds());
5372 }
5373 }
5374
5375 // ---------- remaining roots --------------
5376 _timer.reset();
5377 _timer.start();
5378 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5379 false, // yg was scanned above
5380 false, // this is parallel code
5381 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5382 &par_mrias_cl,
5383 NULL,
5384 NULL); // The dirty klasses will be handled below
5385 assert(_collector->should_unload_classes()
5386 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5387 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5388 _timer.stop();
5389 if (PrintCMSStatistics != 0) {
5390 gclog_or_tty->print_cr(
5391 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5392 worker_id, _timer.seconds());
5393 }
5394
5395 // ---------- unhandled CLD scanning ----------
5396 if (worker_id == 0) { // Single threaded at the moment.
5397 _timer.reset();
5398 _timer.start();
5399
5400 // Scan all new class loader data objects and new dependencies that were
5401 // introduced during concurrent marking.
5402 ResourceMark rm;
5403 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5404 for (int i = 0; i < array->length(); i++) {
5405 par_mrias_cl.do_class_loader_data(array->at(i));
5406 }
5407
5408 // We don't need to keep track of new CLDs anymore.
5409 ClassLoaderDataGraph::remember_new_clds(false);
5410
5411 _timer.stop();
5412 if (PrintCMSStatistics != 0) {
5413 gclog_or_tty->print_cr(
5414 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5415 worker_id, _timer.seconds());
5416 }
5417 }
5418
5419 // ---------- dirty klass scanning ----------
5420 if (worker_id == 0) { // Single threaded at the moment.
5421 _timer.reset();
5422 _timer.start();
5423
5424 // Scan all classes that was dirtied during the concurrent marking phase.
5425 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5426 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5427
5428 _timer.stop();
5429 if (PrintCMSStatistics != 0) {
5430 gclog_or_tty->print_cr(
5431 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5432 worker_id, _timer.seconds());
5433 }
5434 }
5435
5436 // We might have added oops to ClassLoaderData::_handles during the
5437 // concurrent marking phase. These oops point to newly allocated objects
5438 // that are guaranteed to be kept alive. Either by the direct allocation
5439 // code, or when the young collector processes the strong roots. Hence,
5440 // we don't have to revisit the _handles block during the remark phase.
5441
5442 // ---------- rescan dirty cards ------------
5443 _timer.reset();
5444 _timer.start();
5445
5446 // Do the rescan tasks for each of the two spaces
5447 // (cms_space) in turn.
5448 // "worker_id" is passed to select the task_queue for "worker_id"
5449 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5450 _timer.stop();
5451 if (PrintCMSStatistics != 0) {
5452 gclog_or_tty->print_cr(
5453 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5454 worker_id, _timer.seconds());
5455 }
5456
5457 // ---------- steal work from other threads ...
5458 // ---------- ... and drain overflow list.
5459 _timer.reset();
5460 _timer.start();
5461 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5462 _timer.stop();
5463 if (PrintCMSStatistics != 0) {
5464 gclog_or_tty->print_cr(
5465 "Finished work stealing in %dth thread: %3.3f sec",
5466 worker_id, _timer.seconds());
5467 }
5468 }
5469
5470 // Note that parameter "i" is not used.
5471 void
5472 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5473 OopsInGenClosure* cl, ContiguousSpace* space,
5474 HeapWord** chunk_array, size_t chunk_top) {
5475 // Until all tasks completed:
5476 // . claim an unclaimed task
5477 // . compute region boundaries corresponding to task claimed
5478 // using chunk_array
5479 // . par_oop_iterate(cl) over that region
5480
5481 ResourceMark rm;
5482 HandleMark hm;
5483
5484 SequentialSubTasksDone* pst = space->par_seq_tasks();
5485
5486 uint nth_task = 0;
5487 uint n_tasks = pst->n_tasks();
5488
5489 if (n_tasks > 0) {
5490 assert(pst->valid(), "Uninitialized use?");
5491 HeapWord *start, *end;
5492 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5493 // We claimed task # nth_task; compute its boundaries.
5494 if (chunk_top == 0) { // no samples were taken
5495 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5496 start = space->bottom();
5497 end = space->top();
5498 } else if (nth_task == 0) {
5499 start = space->bottom();
5500 end = chunk_array[nth_task];
5501 } else if (nth_task < (uint)chunk_top) {
5502 assert(nth_task >= 1, "Control point invariant");
5503 start = chunk_array[nth_task - 1];
5504 end = chunk_array[nth_task];
5505 } else {
5506 assert(nth_task == (uint)chunk_top, "Control point invariant");
5507 start = chunk_array[chunk_top - 1];
5508 end = space->top();
5509 }
5510 MemRegion mr(start, end);
5511 // Verify that mr is in space
5512 assert(mr.is_empty() || space->used_region().contains(mr),
5513 "Should be in space");
5514 // Verify that "start" is an object boundary
5515 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5516 "Should be an oop");
5517 space->par_oop_iterate(mr, cl);
5518 }
5519 pst->all_tasks_completed();
5520 }
5521 }
5522
5523 void
5524 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5525 CompactibleFreeListSpace* sp, int i,
5526 Par_MarkRefsIntoAndScanClosure* cl) {
5527 // Until all tasks completed:
5528 // . claim an unclaimed task
5529 // . compute region boundaries corresponding to task claimed
5530 // . transfer dirty bits ct->mut for that region
5531 // . apply rescanclosure to dirty mut bits for that region
5532
5533 ResourceMark rm;
5534 HandleMark hm;
5535
5536 OopTaskQueue* work_q = work_queue(i);
5537 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5538 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5539 // CAUTION: This closure has state that persists across calls to
5540 // the work method dirty_range_iterate_clear() in that it has
5541 // embedded in it a (subtype of) UpwardsObjectClosure. The
5542 // use of that state in the embedded UpwardsObjectClosure instance
5543 // assumes that the cards are always iterated (even if in parallel
5544 // by several threads) in monotonically increasing order per each
5545 // thread. This is true of the implementation below which picks
5546 // card ranges (chunks) in monotonically increasing order globally
5547 // and, a-fortiori, in monotonically increasing order per thread
5548 // (the latter order being a subsequence of the former).
5549 // If the work code below is ever reorganized into a more chaotic
5550 // work-partitioning form than the current "sequential tasks"
5551 // paradigm, the use of that persistent state will have to be
5552 // revisited and modified appropriately. See also related
5553 // bug 4756801 work on which should examine this code to make
5554 // sure that the changes there do not run counter to the
5555 // assumptions made here and necessary for correctness and
5556 // efficiency. Note also that this code might yield inefficient
5557 // behavior in the case of very large objects that span one or
5558 // more work chunks. Such objects would potentially be scanned
5559 // several times redundantly. Work on 4756801 should try and
5560 // address that performance anomaly if at all possible. XXX
5561 MemRegion full_span = _collector->_span;
5562 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5563 MarkFromDirtyCardsClosure
5564 greyRescanClosure(_collector, full_span, // entire span of interest
5565 sp, bm, work_q, cl);
5566
5567 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5568 assert(pst->valid(), "Uninitialized use?");
5569 uint nth_task = 0;
5570 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5571 MemRegion span = sp->used_region();
5572 HeapWord* start_addr = span.start();
5573 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5574 alignment);
5575 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5576 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5577 start_addr, "Check alignment");
5578 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5579 chunk_size, "Check alignment");
5580
5581 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5582 // Having claimed the nth_task, compute corresponding mem-region,
5583 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
5584 // The alignment restriction ensures that we do not need any
5585 // synchronization with other gang-workers while setting or
5586 // clearing bits in thus chunk of the MUT.
5587 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5588 start_addr + (nth_task+1)*chunk_size);
5589 // The last chunk's end might be way beyond end of the
5590 // used region. In that case pull back appropriately.
5591 if (this_span.end() > end_addr) {
5592 this_span.set_end(end_addr);
5593 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5594 }
5595 // Iterate over the dirty cards covering this chunk, marking them
5596 // precleaned, and setting the corresponding bits in the mod union
5597 // table. Since we have been careful to partition at Card and MUT-word
5598 // boundaries no synchronization is needed between parallel threads.
5599 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5600 &modUnionClosure);
5601
5602 // Having transferred these marks into the modUnionTable,
5603 // rescan the marked objects on the dirty cards in the modUnionTable.
5604 // Even if this is at a synchronous collection, the initial marking
5605 // may have been done during an asynchronous collection so there
5606 // may be dirty bits in the mod-union table.
5607 _collector->_modUnionTable.dirty_range_iterate_clear(
5608 this_span, &greyRescanClosure);
5609 _collector->_modUnionTable.verifyNoOneBitsInRange(
5610 this_span.start(),
5611 this_span.end());
5612 }
5613 pst->all_tasks_completed(); // declare that i am done
5614 }
5615
5616 // . see if we can share work_queues with ParNew? XXX
5617 void
5618 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5619 int* seed) {
5620 OopTaskQueue* work_q = work_queue(i);
5621 NOT_PRODUCT(int num_steals = 0;)
5622 oop obj_to_scan;
5623 CMSBitMap* bm = &(_collector->_markBitMap);
5624
5625 while (true) {
5626 // Completely finish any left over work from (an) earlier round(s)
5627 cl->trim_queue(0);
5628 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5629 (size_t)ParGCDesiredObjsFromOverflowList);
5630 // Now check if there's any work in the overflow list
5631 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5632 // only affects the number of attempts made to get work from the
5633 // overflow list and does not affect the number of workers. Just
5634 // pass ParallelGCThreads so this behavior is unchanged.
5635 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5636 work_q,
5637 ParallelGCThreads)) {
5638 // found something in global overflow list;
5639 // not yet ready to go stealing work from others.
5640 // We'd like to assert(work_q->size() != 0, ...)
5641 // because we just took work from the overflow list,
5642 // but of course we can't since all of that could have
5643 // been already stolen from us.
5644 // "He giveth and He taketh away."
5645 continue;
5646 }
5647 // Verify that we have no work before we resort to stealing
5648 assert(work_q->size() == 0, "Have work, shouldn't steal");
5649 // Try to steal from other queues that have work
5650 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5651 NOT_PRODUCT(num_steals++;)
5652 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5653 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5654 // Do scanning work
5655 obj_to_scan->oop_iterate(cl);
5656 // Loop around, finish this work, and try to steal some more
5657 } else if (terminator()->offer_termination()) {
5658 break; // nirvana from the infinite cycle
5659 }
5660 }
5661 NOT_PRODUCT(
5662 if (PrintCMSStatistics != 0) {
5663 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5664 }
5665 )
5666 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5667 "Else our work is not yet done");
5668 }
5669
5670 // Record object boundaries in _eden_chunk_array by sampling the eden
5671 // top in the slow-path eden object allocation code path and record
5672 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5673 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5674 // sampling in sample_eden() that activates during the part of the
5675 // preclean phase.
5676 void CMSCollector::sample_eden_chunk() {
5677 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5678 if (_eden_chunk_lock->try_lock()) {
5679 // Record a sample. This is the critical section. The contents
5680 // of the _eden_chunk_array have to be non-decreasing in the
5681 // address order.
5682 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5683 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5684 "Unexpected state of Eden");
5685 if (_eden_chunk_index == 0 ||
5686 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5687 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5688 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5689 _eden_chunk_index++; // commit sample
5690 }
5691 _eden_chunk_lock->unlock();
5692 }
5693 }
5694 }
5695
5696 // Return a thread-local PLAB recording array, as appropriate.
5697 void* CMSCollector::get_data_recorder(int thr_num) {
5698 if (_survivor_plab_array != NULL &&
5699 (CMSPLABRecordAlways ||
5700 (_collectorState > Marking && _collectorState < FinalMarking))) {
5701 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5702 ChunkArray* ca = &_survivor_plab_array[thr_num];
5703 ca->reset(); // clear it so that fresh data is recorded
5704 return (void*) ca;
5705 } else {
5706 return NULL;
5707 }
5708 }
5709
5710 // Reset all the thread-local PLAB recording arrays
5711 void CMSCollector::reset_survivor_plab_arrays() {
5712 for (uint i = 0; i < ParallelGCThreads; i++) {
5713 _survivor_plab_array[i].reset();
5714 }
5715 }
5716
5717 // Merge the per-thread plab arrays into the global survivor chunk
5718 // array which will provide the partitioning of the survivor space
5719 // for CMS initial scan and rescan.
5720 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5721 int no_of_gc_threads) {
5722 assert(_survivor_plab_array != NULL, "Error");
5723 assert(_survivor_chunk_array != NULL, "Error");
5724 assert(_collectorState == FinalMarking ||
5725 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5726 for (int j = 0; j < no_of_gc_threads; j++) {
5727 _cursor[j] = 0;
5728 }
5729 HeapWord* top = surv->top();
5730 size_t i;
5731 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5732 HeapWord* min_val = top; // Higher than any PLAB address
5733 uint min_tid = 0; // position of min_val this round
5734 for (int j = 0; j < no_of_gc_threads; j++) {
5735 ChunkArray* cur_sca = &_survivor_plab_array[j];
5736 if (_cursor[j] == cur_sca->end()) {
5737 continue;
5738 }
5739 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5740 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5741 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5742 if (cur_val < min_val) {
5743 min_tid = j;
5744 min_val = cur_val;
5745 } else {
5746 assert(cur_val < top, "All recorded addresses should be less");
5747 }
5748 }
5749 // At this point min_val and min_tid are respectively
5750 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5751 // and the thread (j) that witnesses that address.
5752 // We record this address in the _survivor_chunk_array[i]
5753 // and increment _cursor[min_tid] prior to the next round i.
5754 if (min_val == top) {
5755 break;
5756 }
5757 _survivor_chunk_array[i] = min_val;
5758 _cursor[min_tid]++;
5759 }
5760 // We are all done; record the size of the _survivor_chunk_array
5761 _survivor_chunk_index = i; // exclusive: [0, i)
5762 if (PrintCMSStatistics > 0) {
5763 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5764 }
5765 // Verify that we used up all the recorded entries
5766 #ifdef ASSERT
5767 size_t total = 0;
5768 for (int j = 0; j < no_of_gc_threads; j++) {
5769 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5770 total += _cursor[j];
5771 }
5772 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5773 // Check that the merged array is in sorted order
5774 if (total > 0) {
5775 for (size_t i = 0; i < total - 1; i++) {
5776 if (PrintCMSStatistics > 0) {
5777 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5778 i, _survivor_chunk_array[i]);
5779 }
5780 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5781 "Not sorted");
5782 }
5783 }
5784 #endif // ASSERT
5785 }
5786
5787 // Set up the space's par_seq_tasks structure for work claiming
5788 // for parallel initial scan and rescan of young gen.
5789 // See ParRescanTask where this is currently used.
5790 void
5791 CMSCollector::
5792 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5793 assert(n_threads > 0, "Unexpected n_threads argument");
5794 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5795
5796 // Eden space
5797 if (!dng->eden()->is_empty()) {
5798 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5799 assert(!pst->valid(), "Clobbering existing data?");
5800 // Each valid entry in [0, _eden_chunk_index) represents a task.
5801 size_t n_tasks = _eden_chunk_index + 1;
5802 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5803 // Sets the condition for completion of the subtask (how many threads
5804 // need to finish in order to be done).
5805 pst->set_n_threads(n_threads);
5806 pst->set_n_tasks((int)n_tasks);
5807 }
5808
5809 // Merge the survivor plab arrays into _survivor_chunk_array
5810 if (_survivor_plab_array != NULL) {
5811 merge_survivor_plab_arrays(dng->from(), n_threads);
5812 } else {
5813 assert(_survivor_chunk_index == 0, "Error");
5814 }
5815
5816 // To space
5817 {
5818 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5819 assert(!pst->valid(), "Clobbering existing data?");
5820 // Sets the condition for completion of the subtask (how many threads
5821 // need to finish in order to be done).
5822 pst->set_n_threads(n_threads);
5823 pst->set_n_tasks(1);
5824 assert(pst->valid(), "Error");
5825 }
5826
5827 // From space
5828 {
5829 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5830 assert(!pst->valid(), "Clobbering existing data?");
5831 size_t n_tasks = _survivor_chunk_index + 1;
5832 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5833 // Sets the condition for completion of the subtask (how many threads
5834 // need to finish in order to be done).
5835 pst->set_n_threads(n_threads);
5836 pst->set_n_tasks((int)n_tasks);
5837 assert(pst->valid(), "Error");
5838 }
5839 }
5840
5841 // Parallel version of remark
5842 void CMSCollector::do_remark_parallel() {
5843 GenCollectedHeap* gch = GenCollectedHeap::heap();
5844 FlexibleWorkGang* workers = gch->workers();
5845 assert(workers != NULL, "Need parallel worker threads.");
5846 // Choose to use the number of GC workers most recently set
5847 // into "active_workers". If active_workers is not set, set it
5848 // to ParallelGCThreads.
5849 int n_workers = workers->active_workers();
5850 if (n_workers == 0) {
5851 assert(n_workers > 0, "Should have been set during scavenge");
5852 n_workers = ParallelGCThreads;
5853 workers->set_active_workers(n_workers);
5854 }
5855 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5856
5857 CMSParRemarkTask tsk(this,
5858 cms_space,
5859 n_workers, workers, task_queues());
5860
5861 // Set up for parallel process_strong_roots work.
5862 gch->set_par_threads(n_workers);
5863 // We won't be iterating over the cards in the card table updating
5864 // the younger_gen cards, so we shouldn't call the following else
5865 // the verification code as well as subsequent younger_refs_iterate
5866 // code would get confused. XXX
5867 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5868
5869 // The young gen rescan work will not be done as part of
5870 // process_strong_roots (which currently doesn't knw how to
5871 // parallelize such a scan), but rather will be broken up into
5872 // a set of parallel tasks (via the sampling that the [abortable]
5873 // preclean phase did of EdenSpace, plus the [two] tasks of
5874 // scanning the [two] survivor spaces. Further fine-grain
5875 // parallelization of the scanning of the survivor spaces
5876 // themselves, and of precleaning of the younger gen itself
5877 // is deferred to the future.
5878 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5879
5880 // The dirty card rescan work is broken up into a "sequence"
5881 // of parallel tasks (per constituent space) that are dynamically
5882 // claimed by the parallel threads.
5883 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5884
5885 // It turns out that even when we're using 1 thread, doing the work in a
5886 // separate thread causes wide variance in run times. We can't help this
5887 // in the multi-threaded case, but we special-case n=1 here to get
5888 // repeatable measurements of the 1-thread overhead of the parallel code.
5889 if (n_workers > 1) {
5890 // Make refs discovery MT-safe, if it isn't already: it may not
5891 // necessarily be so, since it's possible that we are doing
5892 // ST marking.
5893 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5894 GenCollectedHeap::StrongRootsScope srs(gch);
5895 workers->run_task(&tsk);
5896 } else {
5897 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5898 GenCollectedHeap::StrongRootsScope srs(gch);
5899 tsk.work(0);
5900 }
5901
5902 gch->set_par_threads(0); // 0 ==> non-parallel.
5903 // restore, single-threaded for now, any preserved marks
5904 // as a result of work_q overflow
5905 restore_preserved_marks_if_any();
5906 }
5907
5908 // Non-parallel version of remark
5909 void CMSCollector::do_remark_non_parallel() {
5910 ResourceMark rm;
5911 HandleMark hm;
5912 GenCollectedHeap* gch = GenCollectedHeap::heap();
5913 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5914
5915 MarkRefsIntoAndScanClosure
5916 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5917 &_markStack, this,
5918 false /* should_yield */, false /* not precleaning */);
5919 MarkFromDirtyCardsClosure
5920 markFromDirtyCardsClosure(this, _span,
5921 NULL, // space is set further below
5922 &_markBitMap, &_markStack, &mrias_cl);
5923 {
5924 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5925 // Iterate over the dirty cards, setting the corresponding bits in the
5926 // mod union table.
5927 {
5928 ModUnionClosure modUnionClosure(&_modUnionTable);
5929 _ct->ct_bs()->dirty_card_iterate(
5930 _cmsGen->used_region(),
5931 &modUnionClosure);
5932 }
5933 // Having transferred these marks into the modUnionTable, we just need
5934 // to rescan the marked objects on the dirty cards in the modUnionTable.
5935 // The initial marking may have been done during an asynchronous
5936 // collection so there may be dirty bits in the mod-union table.
5937 const int alignment =
5938 CardTableModRefBS::card_size * BitsPerWord;
5939 {
5940 // ... First handle dirty cards in CMS gen
5941 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5942 MemRegion ur = _cmsGen->used_region();
5943 HeapWord* lb = ur.start();
5944 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5945 MemRegion cms_span(lb, ub);
5946 _modUnionTable.dirty_range_iterate_clear(cms_span,
5947 &markFromDirtyCardsClosure);
5948 verify_work_stacks_empty();
5949 if (PrintCMSStatistics != 0) {
5950 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5951 markFromDirtyCardsClosure.num_dirty_cards());
5952 }
5953 }
5954 }
5955 if (VerifyDuringGC &&
5956 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5957 HandleMark hm; // Discard invalid handles created during verification
5958 Universe::verify();
5959 }
5960 {
5961 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5962
5963 verify_work_stacks_empty();
5964
5965 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5966 GenCollectedHeap::StrongRootsScope srs(gch);
5967 gch->gen_process_strong_roots(_cmsGen->level(),
5968 true, // younger gens as roots
5969 false, // use the local StrongRootsScope
5970 SharedHeap::ScanningOption(roots_scanning_options()),
5971 &mrias_cl,
5972 NULL,
5973 NULL); // The dirty klasses will be handled below
5974
5975 assert(should_unload_classes()
5976 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5977 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5978 }
5979
5980 {
5981 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5982
5983 verify_work_stacks_empty();
5984
5985 // Scan all class loader data objects that might have been introduced
5986 // during concurrent marking.
5987 ResourceMark rm;
5988 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5989 for (int i = 0; i < array->length(); i++) {
5990 mrias_cl.do_class_loader_data(array->at(i));
5991 }
5992
5993 // We don't need to keep track of new CLDs anymore.
5994 ClassLoaderDataGraph::remember_new_clds(false);
5995
5996 verify_work_stacks_empty();
5997 }
5998
5999 {
6000 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
6001
6002 verify_work_stacks_empty();
6003
6004 RemarkKlassClosure remark_klass_closure(&mrias_cl);
6005 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
6006
6007 verify_work_stacks_empty();
6008 }
6009
6010 // We might have added oops to ClassLoaderData::_handles during the
6011 // concurrent marking phase. These oops point to newly allocated objects
6012 // that are guaranteed to be kept alive. Either by the direct allocation
6013 // code, or when the young collector processes the strong roots. Hence,
6014 // we don't have to revisit the _handles block during the remark phase.
6015
6016 verify_work_stacks_empty();
6017 // Restore evacuated mark words, if any, used for overflow list links
6018 if (!CMSOverflowEarlyRestoration) {
6019 restore_preserved_marks_if_any();
6020 }
6021 verify_overflow_empty();
6022 }
6023
6024 ////////////////////////////////////////////////////////
6025 // Parallel Reference Processing Task Proxy Class
6026 ////////////////////////////////////////////////////////
6027 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6028 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6029 CMSCollector* _collector;
6030 CMSBitMap* _mark_bit_map;
6031 const MemRegion _span;
6032 ProcessTask& _task;
6033
6034 public:
6035 CMSRefProcTaskProxy(ProcessTask& task,
6036 CMSCollector* collector,
6037 const MemRegion& span,
6038 CMSBitMap* mark_bit_map,
6039 AbstractWorkGang* workers,
6040 OopTaskQueueSet* task_queues):
6041 // XXX Should superclass AGTWOQ also know about AWG since it knows
6042 // about the task_queues used by the AWG? Then it could initialize
6043 // the terminator() object. See 6984287. The set_for_termination()
6044 // below is a temporary band-aid for the regression in 6984287.
6045 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6046 task_queues),
6047 _task(task),
6048 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6049 {
6050 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6051 "Inconsistency in _span");
6052 set_for_termination(workers->active_workers());
6053 }
6054
6055 OopTaskQueueSet* task_queues() { return queues(); }
6056
6057 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6058
6059 void do_work_steal(int i,
6060 CMSParDrainMarkingStackClosure* drain,
6061 CMSParKeepAliveClosure* keep_alive,
6062 int* seed);
6063
6064 virtual void work(uint worker_id);
6065 };
6066
6067 void CMSRefProcTaskProxy::work(uint worker_id) {
6068 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6069 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6070 _mark_bit_map,
6071 work_queue(worker_id));
6072 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6073 _mark_bit_map,
6074 work_queue(worker_id));
6075 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6076 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6077 if (_task.marks_oops_alive()) {
6078 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6079 _collector->hash_seed(worker_id));
6080 }
6081 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6082 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6083 }
6084
6085 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6086 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6087 EnqueueTask& _task;
6088
6089 public:
6090 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6091 : AbstractGangTask("Enqueue reference objects in parallel"),
6092 _task(task)
6093 { }
6094
6095 virtual void work(uint worker_id)
6096 {
6097 _task.work(worker_id);
6098 }
6099 };
6100
6101 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6102 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6103 _span(span),
6104 _bit_map(bit_map),
6105 _work_queue(work_queue),
6106 _mark_and_push(collector, span, bit_map, work_queue),
6107 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6108 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6109 { }
6110
6111 // . see if we can share work_queues with ParNew? XXX
6112 void CMSRefProcTaskProxy::do_work_steal(int i,
6113 CMSParDrainMarkingStackClosure* drain,
6114 CMSParKeepAliveClosure* keep_alive,
6115 int* seed) {
6116 OopTaskQueue* work_q = work_queue(i);
6117 NOT_PRODUCT(int num_steals = 0;)
6118 oop obj_to_scan;
6119
6120 while (true) {
6121 // Completely finish any left over work from (an) earlier round(s)
6122 drain->trim_queue(0);
6123 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6124 (size_t)ParGCDesiredObjsFromOverflowList);
6125 // Now check if there's any work in the overflow list
6126 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6127 // only affects the number of attempts made to get work from the
6128 // overflow list and does not affect the number of workers. Just
6129 // pass ParallelGCThreads so this behavior is unchanged.
6130 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6131 work_q,
6132 ParallelGCThreads)) {
6133 // Found something in global overflow list;
6134 // not yet ready to go stealing work from others.
6135 // We'd like to assert(work_q->size() != 0, ...)
6136 // because we just took work from the overflow list,
6137 // but of course we can't, since all of that might have
6138 // been already stolen from us.
6139 continue;
6140 }
6141 // Verify that we have no work before we resort to stealing
6142 assert(work_q->size() == 0, "Have work, shouldn't steal");
6143 // Try to steal from other queues that have work
6144 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6145 NOT_PRODUCT(num_steals++;)
6146 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6147 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6148 // Do scanning work
6149 obj_to_scan->oop_iterate(keep_alive);
6150 // Loop around, finish this work, and try to steal some more
6151 } else if (terminator()->offer_termination()) {
6152 break; // nirvana from the infinite cycle
6153 }
6154 }
6155 NOT_PRODUCT(
6156 if (PrintCMSStatistics != 0) {
6157 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6158 }
6159 )
6160 }
6161
6162 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6163 {
6164 GenCollectedHeap* gch = GenCollectedHeap::heap();
6165 FlexibleWorkGang* workers = gch->workers();
6166 assert(workers != NULL, "Need parallel worker threads.");
6167 CMSRefProcTaskProxy rp_task(task, &_collector,
6168 _collector.ref_processor()->span(),
6169 _collector.markBitMap(),
6170 workers, _collector.task_queues());
6171 workers->run_task(&rp_task);
6172 }
6173
6174 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6175 {
6176
6177 GenCollectedHeap* gch = GenCollectedHeap::heap();
6178 FlexibleWorkGang* workers = gch->workers();
6179 assert(workers != NULL, "Need parallel worker threads.");
6180 CMSRefEnqueueTaskProxy enq_task(task);
6181 workers->run_task(&enq_task);
6182 }
6183
6184 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6185
6186 ResourceMark rm;
6187 HandleMark hm;
6188
6189 ReferenceProcessor* rp = ref_processor();
6190 assert(rp->span().equals(_span), "Spans should be equal");
6191 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6192 // Process weak references.
6193 rp->setup_policy(clear_all_soft_refs);
6194 verify_work_stacks_empty();
6195
6196 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6197 &_markStack, false /* !preclean */);
6198 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6199 _span, &_markBitMap, &_markStack,
6200 &cmsKeepAliveClosure, false /* !preclean */);
6201 {
6202 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
6203
6204 ReferenceProcessorStats stats;
6205 if (rp->processing_is_mt()) {
6206 // Set the degree of MT here. If the discovery is done MT, there
6207 // may have been a different number of threads doing the discovery
6208 // and a different number of discovered lists may have Ref objects.
6209 // That is OK as long as the Reference lists are balanced (see
6210 // balance_all_queues() and balance_queues()).
6211 GenCollectedHeap* gch = GenCollectedHeap::heap();
6212 int active_workers = ParallelGCThreads;
6213 FlexibleWorkGang* workers = gch->workers();
6214 if (workers != NULL) {
6215 active_workers = workers->active_workers();
6216 // The expectation is that active_workers will have already
6217 // been set to a reasonable value. If it has not been set,
6218 // investigate.
6219 assert(active_workers > 0, "Should have been set during scavenge");
6220 }
6221 rp->set_active_mt_degree(active_workers);
6222 CMSRefProcTaskExecutor task_executor(*this);
6223 stats = rp->process_discovered_references(&_is_alive_closure,
6224 &cmsKeepAliveClosure,
6225 &cmsDrainMarkingStackClosure,
6226 &task_executor,
6227 _gc_timer_cm);
6228 } else {
6229 stats = rp->process_discovered_references(&_is_alive_closure,
6230 &cmsKeepAliveClosure,
6231 &cmsDrainMarkingStackClosure,
6232 NULL,
6233 _gc_timer_cm);
6234 }
6235 _gc_tracer_cm->report_gc_reference_stats(stats);
6236
6237 }
6238
6239 // This is the point where the entire marking should have completed.
6240 verify_work_stacks_empty();
6241
6242 if (should_unload_classes()) {
6243 {
6244 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
6245
6246 // Unload classes and purge the SystemDictionary.
6247 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6248
6249 // Unload nmethods.
6250 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6251
6252 // Prune dead klasses from subklass/sibling/implementor lists.
6253 Klass::clean_weak_klass_links(&_is_alive_closure);
6254 }
6255
6256 {
6257 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6258 // Clean up unreferenced symbols in symbol table.
6259 SymbolTable::unlink();
6260 }
6261 }
6262
6263 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
6264 // Need to check if we really scanned the StringTable.
6265 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6266 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6267 // Delete entries for dead interned strings.
6268 StringTable::unlink(&_is_alive_closure);
6269 }
6270
6271 // Restore any preserved marks as a result of mark stack or
6272 // work queue overflow
6273 restore_preserved_marks_if_any(); // done single-threaded for now
6274
6275 rp->set_enqueuing_is_done(true);
6276 if (rp->processing_is_mt()) {
6277 rp->balance_all_queues();
6278 CMSRefProcTaskExecutor task_executor(*this);
6279 rp->enqueue_discovered_references(&task_executor);
6280 } else {
6281 rp->enqueue_discovered_references(NULL);
6282 }
6283 rp->verify_no_references_recorded();
6284 assert(!rp->discovery_enabled(), "should have been disabled");
6285 }
6286
6287 #ifndef PRODUCT
6288 void CMSCollector::check_correct_thread_executing() {
6289 Thread* t = Thread::current();
6290 // Only the VM thread or the CMS thread should be here.
6291 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6292 "Unexpected thread type");
6293 // If this is the vm thread, the foreground process
6294 // should not be waiting. Note that _foregroundGCIsActive is
6295 // true while the foreground collector is waiting.
6296 if (_foregroundGCShouldWait) {
6297 // We cannot be the VM thread
6298 assert(t->is_ConcurrentGC_thread(),
6299 "Should be CMS thread");
6300 } else {
6301 // We can be the CMS thread only if we are in a stop-world
6302 // phase of CMS collection.
6303 if (t->is_ConcurrentGC_thread()) {
6304 assert(_collectorState == InitialMarking ||
6305 _collectorState == FinalMarking,
6306 "Should be a stop-world phase");
6307 // The CMS thread should be holding the CMS_token.
6308 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6309 "Potential interference with concurrently "
6310 "executing VM thread");
6311 }
6312 }
6313 }
6314 #endif
6315
6316 void CMSCollector::sweep(bool asynch) {
6317 assert(_collectorState == Sweeping, "just checking");
6318 check_correct_thread_executing();
6319 verify_work_stacks_empty();
6320 verify_overflow_empty();
6321 increment_sweep_count();
6322 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6323
6324 _inter_sweep_timer.stop();
6325 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6326 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6327
6328 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6329 _intra_sweep_timer.reset();
6330 _intra_sweep_timer.start();
6331 if (asynch) {
6332 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6333 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6334 // First sweep the old gen
6335 {
6336 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6337 bitMapLock());
6338 sweepWork(_cmsGen, asynch);
6339 }
6340
6341 // Update Universe::_heap_*_at_gc figures.
6342 // We need all the free list locks to make the abstract state
6343 // transition from Sweeping to Resetting. See detailed note
6344 // further below.
6345 {
6346 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6347 // Update heap occupancy information which is used as
6348 // input to soft ref clearing policy at the next gc.
6349 Universe::update_heap_info_at_gc();
6350 _collectorState = Resizing;
6351 }
6352 } else {
6353 // already have needed locks
6354 sweepWork(_cmsGen, asynch);
6355 // Update heap occupancy information which is used as
6356 // input to soft ref clearing policy at the next gc.
6357 Universe::update_heap_info_at_gc();
6358 _collectorState = Resizing;
6359 }
6360 verify_work_stacks_empty();
6361 verify_overflow_empty();
6362
6363 if (should_unload_classes()) {
6364 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6365 // requires that the virtual spaces are stable and not deleted.
6366 ClassLoaderDataGraph::set_should_purge(true);
6367 }
6368
6369 _intra_sweep_timer.stop();
6370 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6371
6372 _inter_sweep_timer.reset();
6373 _inter_sweep_timer.start();
6374
6375 // We need to use a monotonically non-decreasing time in ms
6376 // or we will see time-warp warnings and os::javaTimeMillis()
6377 // does not guarantee monotonicity.
6378 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6379 update_time_of_last_gc(now);
6380
6381 // NOTE on abstract state transitions:
6382 // Mutators allocate-live and/or mark the mod-union table dirty
6383 // based on the state of the collection. The former is done in
6384 // the interval [Marking, Sweeping] and the latter in the interval
6385 // [Marking, Sweeping). Thus the transitions into the Marking state
6386 // and out of the Sweeping state must be synchronously visible
6387 // globally to the mutators.
6388 // The transition into the Marking state happens with the world
6389 // stopped so the mutators will globally see it. Sweeping is
6390 // done asynchronously by the background collector so the transition
6391 // from the Sweeping state to the Resizing state must be done
6392 // under the freelistLock (as is the check for whether to
6393 // allocate-live and whether to dirty the mod-union table).
6394 assert(_collectorState == Resizing, "Change of collector state to"
6395 " Resizing must be done under the freelistLocks (plural)");
6396
6397 // Now that sweeping has been completed, we clear
6398 // the incremental_collection_failed flag,
6399 // thus inviting a younger gen collection to promote into
6400 // this generation. If such a promotion may still fail,
6401 // the flag will be set again when a young collection is
6402 // attempted.
6403 GenCollectedHeap* gch = GenCollectedHeap::heap();
6404 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6405 gch->update_full_collections_completed(_collection_count_start);
6406 }
6407
6408 // FIX ME!!! Looks like this belongs in CFLSpace, with
6409 // CMSGen merely delegating to it.
6410 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6411 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6412 HeapWord* minAddr = _cmsSpace->bottom();
6413 HeapWord* largestAddr =
6414 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6415 if (largestAddr == NULL) {
6416 // The dictionary appears to be empty. In this case
6417 // try to coalesce at the end of the heap.
6418 largestAddr = _cmsSpace->end();
6419 }
6420 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6421 size_t nearLargestOffset =
6422 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6423 if (PrintFLSStatistics != 0) {
6424 gclog_or_tty->print_cr(
6425 "CMS: Large Block: " PTR_FORMAT ";"
6426 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6427 largestAddr,
6428 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6429 }
6430 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6431 }
6432
6433 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6434 return addr >= _cmsSpace->nearLargestChunk();
6435 }
6436
6437 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6438 return _cmsSpace->find_chunk_at_end();
6439 }
6440
6441 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6442 bool full) {
6443 // The next lower level has been collected. Gather any statistics
6444 // that are of interest at this point.
6445 if (!full && (current_level + 1) == level()) {
6446 // Gather statistics on the young generation collection.
6447 collector()->stats().record_gc0_end(used());
6448 }
6449 }
6450
6451 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6452 GenCollectedHeap* gch = GenCollectedHeap::heap();
6453 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6454 "Wrong type of heap");
6455 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6456 gch->gen_policy()->size_policy();
6457 assert(sp->is_gc_cms_adaptive_size_policy(),
6458 "Wrong type of size policy");
6459 return sp;
6460 }
6461
6462 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6463 if (PrintGCDetails && Verbose) {
6464 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6465 }
6466 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6467 _debug_collection_type =
6468 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6469 if (PrintGCDetails && Verbose) {
6470 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6471 }
6472 }
6473
6474 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6475 bool asynch) {
6476 // We iterate over the space(s) underlying this generation,
6477 // checking the mark bit map to see if the bits corresponding
6478 // to specific blocks are marked or not. Blocks that are
6479 // marked are live and are not swept up. All remaining blocks
6480 // are swept up, with coalescing on-the-fly as we sweep up
6481 // contiguous free and/or garbage blocks:
6482 // We need to ensure that the sweeper synchronizes with allocators
6483 // and stop-the-world collectors. In particular, the following
6484 // locks are used:
6485 // . CMS token: if this is held, a stop the world collection cannot occur
6486 // . freelistLock: if this is held no allocation can occur from this
6487 // generation by another thread
6488 // . bitMapLock: if this is held, no other thread can access or update
6489 //
6490
6491 // Note that we need to hold the freelistLock if we use
6492 // block iterate below; else the iterator might go awry if
6493 // a mutator (or promotion) causes block contents to change
6494 // (for instance if the allocator divvies up a block).
6495 // If we hold the free list lock, for all practical purposes
6496 // young generation GC's can't occur (they'll usually need to
6497 // promote), so we might as well prevent all young generation
6498 // GC's while we do a sweeping step. For the same reason, we might
6499 // as well take the bit map lock for the entire duration
6500
6501 // check that we hold the requisite locks
6502 assert(have_cms_token(), "Should hold cms token");
6503 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6504 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6505 "Should possess CMS token to sweep");
6506 assert_lock_strong(gen->freelistLock());
6507 assert_lock_strong(bitMapLock());
6508
6509 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6510 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6511 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6512 _inter_sweep_estimate.padded_average(),
6513 _intra_sweep_estimate.padded_average());
6514 gen->setNearLargestChunk();
6515
6516 {
6517 SweepClosure sweepClosure(this, gen, &_markBitMap,
6518 CMSYield && asynch);
6519 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6520 // We need to free-up/coalesce garbage/blocks from a
6521 // co-terminal free run. This is done in the SweepClosure
6522 // destructor; so, do not remove this scope, else the
6523 // end-of-sweep-census below will be off by a little bit.
6524 }
6525 gen->cmsSpace()->sweep_completed();
6526 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6527 if (should_unload_classes()) { // unloaded classes this cycle,
6528 _concurrent_cycles_since_last_unload = 0; // ... reset count
6529 } else { // did not unload classes,
6530 _concurrent_cycles_since_last_unload++; // ... increment count
6531 }
6532 }
6533
6534 // Reset CMS data structures (for now just the marking bit map)
6535 // preparatory for the next cycle.
6536 void CMSCollector::reset(bool asynch) {
6537 GenCollectedHeap* gch = GenCollectedHeap::heap();
6538 CMSAdaptiveSizePolicy* sp = size_policy();
6539 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6540 if (asynch) {
6541 CMSTokenSyncWithLocks ts(true, bitMapLock());
6542
6543 // If the state is not "Resetting", the foreground thread
6544 // has done a collection and the resetting.
6545 if (_collectorState != Resetting) {
6546 assert(_collectorState == Idling, "The state should only change"
6547 " because the foreground collector has finished the collection");
6548 return;
6549 }
6550
6551 // Clear the mark bitmap (no grey objects to start with)
6552 // for the next cycle.
6553 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6554 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6555
6556 HeapWord* curAddr = _markBitMap.startWord();
6557 while (curAddr < _markBitMap.endWord()) {
6558 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6559 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6560 _markBitMap.clear_large_range(chunk);
6561 if (ConcurrentMarkSweepThread::should_yield() &&
6562 !foregroundGCIsActive() &&
6563 CMSYield) {
6564 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6565 "CMS thread should hold CMS token");
6566 assert_lock_strong(bitMapLock());
6567 bitMapLock()->unlock();
6568 ConcurrentMarkSweepThread::desynchronize(true);
6569 ConcurrentMarkSweepThread::acknowledge_yield_request();
6570 stopTimer();
6571 if (PrintCMSStatistics != 0) {
6572 incrementYields();
6573 }
6574 icms_wait();
6575
6576 // See the comment in coordinator_yield()
6577 for (unsigned i = 0; i < CMSYieldSleepCount &&
6578 ConcurrentMarkSweepThread::should_yield() &&
6579 !CMSCollector::foregroundGCIsActive(); ++i) {
6580 os::sleep(Thread::current(), 1, false);
6581 ConcurrentMarkSweepThread::acknowledge_yield_request();
6582 }
6583
6584 ConcurrentMarkSweepThread::synchronize(true);
6585 bitMapLock()->lock_without_safepoint_check();
6586 startTimer();
6587 }
6588 curAddr = chunk.end();
6589 }
6590 // A successful mostly concurrent collection has been done.
6591 // Because only the full (i.e., concurrent mode failure) collections
6592 // are being measured for gc overhead limits, clean the "near" flag
6593 // and count.
6594 sp->reset_gc_overhead_limit_count();
6595 _collectorState = Idling;
6596 } else {
6597 // already have the lock
6598 assert(_collectorState == Resetting, "just checking");
6599 assert_lock_strong(bitMapLock());
6600 _markBitMap.clear_all();
6601 _collectorState = Idling;
6602 }
6603
6604 // Stop incremental mode after a cycle completes, so that any future cycles
6605 // are triggered by allocation.
6606 stop_icms();
6607
6608 NOT_PRODUCT(
6609 if (RotateCMSCollectionTypes) {
6610 _cmsGen->rotate_debug_collection_type();
6611 }
6612 )
6613
6614 register_gc_end();
6615 }
6616
6617 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6618 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6619 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6620 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6621 TraceCollectorStats tcs(counters());
6622
6623 switch (op) {
6624 case CMS_op_checkpointRootsInitial: {
6625 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6626 checkpointRootsInitial(true); // asynch
6627 if (PrintGC) {
6628 _cmsGen->printOccupancy("initial-mark");
6629 }
6630 break;
6631 }
6632 case CMS_op_checkpointRootsFinal: {
6633 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6634 checkpointRootsFinal(true, // asynch
6635 false, // !clear_all_soft_refs
6636 false); // !init_mark_was_synchronous
6637 if (PrintGC) {
6638 _cmsGen->printOccupancy("remark");
6639 }
6640 break;
6641 }
6642 default:
6643 fatal("No such CMS_op");
6644 }
6645 }
6646
6647 #ifndef PRODUCT
6648 size_t const CMSCollector::skip_header_HeapWords() {
6649 return FreeChunk::header_size();
6650 }
6651
6652 // Try and collect here conditions that should hold when
6653 // CMS thread is exiting. The idea is that the foreground GC
6654 // thread should not be blocked if it wants to terminate
6655 // the CMS thread and yet continue to run the VM for a while
6656 // after that.
6657 void CMSCollector::verify_ok_to_terminate() const {
6658 assert(Thread::current()->is_ConcurrentGC_thread(),
6659 "should be called by CMS thread");
6660 assert(!_foregroundGCShouldWait, "should be false");
6661 // We could check here that all the various low-level locks
6662 // are not held by the CMS thread, but that is overkill; see
6663 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6664 // is checked.
6665 }
6666 #endif
6667
6668 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6669 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6670 "missing Printezis mark?");
6671 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6672 size_t size = pointer_delta(nextOneAddr + 1, addr);
6673 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6674 "alignment problem");
6675 assert(size >= 3, "Necessary for Printezis marks to work");
6676 return size;
6677 }
6678
6679 // A variant of the above (block_size_using_printezis_bits()) except
6680 // that we return 0 if the P-bits are not yet set.
6681 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6682 if (_markBitMap.isMarked(addr + 1)) {
6683 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6684 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6685 size_t size = pointer_delta(nextOneAddr + 1, addr);
6686 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6687 "alignment problem");
6688 assert(size >= 3, "Necessary for Printezis marks to work");
6689 return size;
6690 }
6691 return 0;
6692 }
6693
6694 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6695 size_t sz = 0;
6696 oop p = (oop)addr;
6697 if (p->klass_or_null() != NULL) {
6698 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6699 } else {
6700 sz = block_size_using_printezis_bits(addr);
6701 }
6702 assert(sz > 0, "size must be nonzero");
6703 HeapWord* next_block = addr + sz;
6704 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6705 CardTableModRefBS::card_size);
6706 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6707 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6708 "must be different cards");
6709 return next_card;
6710 }
6711
6712
6713 // CMS Bit Map Wrapper /////////////////////////////////////////
6714
6715 // Construct a CMS bit map infrastructure, but don't create the
6716 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6717 // further below.
6718 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6719 _bm(),
6720 _shifter(shifter),
6721 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6722 {
6723 _bmStartWord = 0;
6724 _bmWordSize = 0;
6725 }
6726
6727 bool CMSBitMap::allocate(MemRegion mr) {
6728 _bmStartWord = mr.start();
6729 _bmWordSize = mr.word_size();
6730 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6731 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6732 if (!brs.is_reserved()) {
6733 warning("CMS bit map allocation failure");
6734 return false;
6735 }
6736 // For now we'll just commit all of the bit map up front.
6737 // Later on we'll try to be more parsimonious with swap.
6738 if (!_virtual_space.initialize(brs, brs.size())) {
6739 warning("CMS bit map backing store failure");
6740 return false;
6741 }
6742 assert(_virtual_space.committed_size() == brs.size(),
6743 "didn't reserve backing store for all of CMS bit map?");
6744 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6745 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6746 _bmWordSize, "inconsistency in bit map sizing");
6747 _bm.set_size(_bmWordSize >> _shifter);
6748
6749 // bm.clear(); // can we rely on getting zero'd memory? verify below
6750 assert(isAllClear(),
6751 "Expected zero'd memory from ReservedSpace constructor");
6752 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6753 "consistency check");
6754 return true;
6755 }
6756
6757 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6758 HeapWord *next_addr, *end_addr, *last_addr;
6759 assert_locked();
6760 assert(covers(mr), "out-of-range error");
6761 // XXX assert that start and end are appropriately aligned
6762 for (next_addr = mr.start(), end_addr = mr.end();
6763 next_addr < end_addr; next_addr = last_addr) {
6764 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6765 last_addr = dirty_region.end();
6766 if (!dirty_region.is_empty()) {
6767 cl->do_MemRegion(dirty_region);
6768 } else {
6769 assert(last_addr == end_addr, "program logic");
6770 return;
6771 }
6772 }
6773 }
6774
6775 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6776 _bm.print_on_error(st, prefix);
6777 }
6778
6779 #ifndef PRODUCT
6780 void CMSBitMap::assert_locked() const {
6781 CMSLockVerifier::assert_locked(lock());
6782 }
6783
6784 bool CMSBitMap::covers(MemRegion mr) const {
6785 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6786 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6787 "size inconsistency");
6788 return (mr.start() >= _bmStartWord) &&
6789 (mr.end() <= endWord());
6790 }
6791
6792 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6793 return (start >= _bmStartWord && (start + size) <= endWord());
6794 }
6795
6796 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6797 // verify that there are no 1 bits in the interval [left, right)
6798 FalseBitMapClosure falseBitMapClosure;
6799 iterate(&falseBitMapClosure, left, right);
6800 }
6801
6802 void CMSBitMap::region_invariant(MemRegion mr)
6803 {
6804 assert_locked();
6805 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6806 assert(!mr.is_empty(), "unexpected empty region");
6807 assert(covers(mr), "mr should be covered by bit map");
6808 // convert address range into offset range
6809 size_t start_ofs = heapWordToOffset(mr.start());
6810 // Make sure that end() is appropriately aligned
6811 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6812 (1 << (_shifter+LogHeapWordSize))),
6813 "Misaligned mr.end()");
6814 size_t end_ofs = heapWordToOffset(mr.end());
6815 assert(end_ofs > start_ofs, "Should mark at least one bit");
6816 }
6817
6818 #endif
6819
6820 bool CMSMarkStack::allocate(size_t size) {
6821 // allocate a stack of the requisite depth
6822 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6823 size * sizeof(oop)));
6824 if (!rs.is_reserved()) {
6825 warning("CMSMarkStack allocation failure");
6826 return false;
6827 }
6828 if (!_virtual_space.initialize(rs, rs.size())) {
6829 warning("CMSMarkStack backing store failure");
6830 return false;
6831 }
6832 assert(_virtual_space.committed_size() == rs.size(),
6833 "didn't reserve backing store for all of CMS stack?");
6834 _base = (oop*)(_virtual_space.low());
6835 _index = 0;
6836 _capacity = size;
6837 NOT_PRODUCT(_max_depth = 0);
6838 return true;
6839 }
6840
6841 // XXX FIX ME !!! In the MT case we come in here holding a
6842 // leaf lock. For printing we need to take a further lock
6843 // which has lower rank. We need to recalibrate the two
6844 // lock-ranks involved in order to be able to print the
6845 // messages below. (Or defer the printing to the caller.
6846 // For now we take the expedient path of just disabling the
6847 // messages for the problematic case.)
6848 void CMSMarkStack::expand() {
6849 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6850 if (_capacity == MarkStackSizeMax) {
6851 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6852 // We print a warning message only once per CMS cycle.
6853 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6854 }
6855 return;
6856 }
6857 // Double capacity if possible
6858 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6859 // Do not give up existing stack until we have managed to
6860 // get the double capacity that we desired.
6861 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6862 new_capacity * sizeof(oop)));
6863 if (rs.is_reserved()) {
6864 // Release the backing store associated with old stack
6865 _virtual_space.release();
6866 // Reinitialize virtual space for new stack
6867 if (!_virtual_space.initialize(rs, rs.size())) {
6868 fatal("Not enough swap for expanded marking stack");
6869 }
6870 _base = (oop*)(_virtual_space.low());
6871 _index = 0;
6872 _capacity = new_capacity;
6873 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6874 // Failed to double capacity, continue;
6875 // we print a detail message only once per CMS cycle.
6876 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6877 SIZE_FORMAT"K",
6878 _capacity / K, new_capacity / K);
6879 }
6880 }
6881
6882
6883 // Closures
6884 // XXX: there seems to be a lot of code duplication here;
6885 // should refactor and consolidate common code.
6886
6887 // This closure is used to mark refs into the CMS generation in
6888 // the CMS bit map. Called at the first checkpoint. This closure
6889 // assumes that we do not need to re-mark dirty cards; if the CMS
6890 // generation on which this is used is not an oldest
6891 // generation then this will lose younger_gen cards!
6892
6893 MarkRefsIntoClosure::MarkRefsIntoClosure(
6894 MemRegion span, CMSBitMap* bitMap):
6895 _span(span),
6896 _bitMap(bitMap)
6897 {
6898 assert(_ref_processor == NULL, "deliberately left NULL");
6899 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6900 }
6901
6902 void MarkRefsIntoClosure::do_oop(oop obj) {
6903 // if p points into _span, then mark corresponding bit in _markBitMap
6904 assert(obj->is_oop(), "expected an oop");
6905 HeapWord* addr = (HeapWord*)obj;
6906 if (_span.contains(addr)) {
6907 // this should be made more efficient
6908 _bitMap->mark(addr);
6909 }
6910 }
6911
6912 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6913 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6914
6915 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6916 MemRegion span, CMSBitMap* bitMap):
6917 _span(span),
6918 _bitMap(bitMap)
6919 {
6920 assert(_ref_processor == NULL, "deliberately left NULL");
6921 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6922 }
6923
6924 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6925 // if p points into _span, then mark corresponding bit in _markBitMap
6926 assert(obj->is_oop(), "expected an oop");
6927 HeapWord* addr = (HeapWord*)obj;
6928 if (_span.contains(addr)) {
6929 // this should be made more efficient
6930 _bitMap->par_mark(addr);
6931 }
6932 }
6933
6934 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6935 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6936
6937 // A variant of the above, used for CMS marking verification.
6938 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6939 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6940 _span(span),
6941 _verification_bm(verification_bm),
6942 _cms_bm(cms_bm)
6943 {
6944 assert(_ref_processor == NULL, "deliberately left NULL");
6945 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6946 }
6947
6948 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6949 // if p points into _span, then mark corresponding bit in _markBitMap
6950 assert(obj->is_oop(), "expected an oop");
6951 HeapWord* addr = (HeapWord*)obj;
6952 if (_span.contains(addr)) {
6953 _verification_bm->mark(addr);
6954 if (!_cms_bm->isMarked(addr)) {
6955 oop(addr)->print();
6956 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6957 fatal("... aborting");
6958 }
6959 }
6960 }
6961
6962 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6963 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6964
6965 //////////////////////////////////////////////////
6966 // MarkRefsIntoAndScanClosure
6967 //////////////////////////////////////////////////
6968
6969 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6970 ReferenceProcessor* rp,
6971 CMSBitMap* bit_map,
6972 CMSBitMap* mod_union_table,
6973 CMSMarkStack* mark_stack,
6974 CMSCollector* collector,
6975 bool should_yield,
6976 bool concurrent_precleaning):
6977 _collector(collector),
6978 _span(span),
6979 _bit_map(bit_map),
6980 _mark_stack(mark_stack),
6981 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6982 mark_stack, concurrent_precleaning),
6983 _yield(should_yield),
6984 _concurrent_precleaning(concurrent_precleaning),
6985 _freelistLock(NULL)
6986 {
6987 _ref_processor = rp;
6988 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6989 }
6990
6991 // This closure is used to mark refs into the CMS generation at the
6992 // second (final) checkpoint, and to scan and transitively follow
6993 // the unmarked oops. It is also used during the concurrent precleaning
6994 // phase while scanning objects on dirty cards in the CMS generation.
6995 // The marks are made in the marking bit map and the marking stack is
6996 // used for keeping the (newly) grey objects during the scan.
6997 // The parallel version (Par_...) appears further below.
6998 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6999 if (obj != NULL) {
7000 assert(obj->is_oop(), "expected an oop");
7001 HeapWord* addr = (HeapWord*)obj;
7002 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7003 assert(_collector->overflow_list_is_empty(),
7004 "overflow list should be empty");
7005 if (_span.contains(addr) &&
7006 !_bit_map->isMarked(addr)) {
7007 // mark bit map (object is now grey)
7008 _bit_map->mark(addr);
7009 // push on marking stack (stack should be empty), and drain the
7010 // stack by applying this closure to the oops in the oops popped
7011 // from the stack (i.e. blacken the grey objects)
7012 bool res = _mark_stack->push(obj);
7013 assert(res, "Should have space to push on empty stack");
7014 do {
7015 oop new_oop = _mark_stack->pop();
7016 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7017 assert(_bit_map->isMarked((HeapWord*)new_oop),
7018 "only grey objects on this stack");
7019 // iterate over the oops in this oop, marking and pushing
7020 // the ones in CMS heap (i.e. in _span).
7021 new_oop->oop_iterate(&_pushAndMarkClosure);
7022 // check if it's time to yield
7023 do_yield_check();
7024 } while (!_mark_stack->isEmpty() ||
7025 (!_concurrent_precleaning && take_from_overflow_list()));
7026 // if marking stack is empty, and we are not doing this
7027 // during precleaning, then check the overflow list
7028 }
7029 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7030 assert(_collector->overflow_list_is_empty(),
7031 "overflow list was drained above");
7032 // We could restore evacuated mark words, if any, used for
7033 // overflow list links here because the overflow list is
7034 // provably empty here. That would reduce the maximum
7035 // size requirements for preserved_{oop,mark}_stack.
7036 // But we'll just postpone it until we are all done
7037 // so we can just stream through.
7038 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7039 _collector->restore_preserved_marks_if_any();
7040 assert(_collector->no_preserved_marks(), "No preserved marks");
7041 }
7042 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7043 "All preserved marks should have been restored above");
7044 }
7045 }
7046
7047 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7048 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7049
7050 void MarkRefsIntoAndScanClosure::do_yield_work() {
7051 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7052 "CMS thread should hold CMS token");
7053 assert_lock_strong(_freelistLock);
7054 assert_lock_strong(_bit_map->lock());
7055 // relinquish the free_list_lock and bitMaplock()
7056 _bit_map->lock()->unlock();
7057 _freelistLock->unlock();
7058 ConcurrentMarkSweepThread::desynchronize(true);
7059 ConcurrentMarkSweepThread::acknowledge_yield_request();
7060 _collector->stopTimer();
7061 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7062 if (PrintCMSStatistics != 0) {
7063 _collector->incrementYields();
7064 }
7065 _collector->icms_wait();
7066
7067 // See the comment in coordinator_yield()
7068 for (unsigned i = 0;
7069 i < CMSYieldSleepCount &&
7070 ConcurrentMarkSweepThread::should_yield() &&
7071 !CMSCollector::foregroundGCIsActive();
7072 ++i) {
7073 os::sleep(Thread::current(), 1, false);
7074 ConcurrentMarkSweepThread::acknowledge_yield_request();
7075 }
7076
7077 ConcurrentMarkSweepThread::synchronize(true);
7078 _freelistLock->lock_without_safepoint_check();
7079 _bit_map->lock()->lock_without_safepoint_check();
7080 _collector->startTimer();
7081 }
7082
7083 ///////////////////////////////////////////////////////////
7084 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7085 // MarkRefsIntoAndScanClosure
7086 ///////////////////////////////////////////////////////////
7087 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7088 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7089 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7090 _span(span),
7091 _bit_map(bit_map),
7092 _work_queue(work_queue),
7093 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7094 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7095 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7096 {
7097 _ref_processor = rp;
7098 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7099 }
7100
7101 // This closure is used to mark refs into the CMS generation at the
7102 // second (final) checkpoint, and to scan and transitively follow
7103 // the unmarked oops. The marks are made in the marking bit map and
7104 // the work_queue is used for keeping the (newly) grey objects during
7105 // the scan phase whence they are also available for stealing by parallel
7106 // threads. Since the marking bit map is shared, updates are
7107 // synchronized (via CAS).
7108 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7109 if (obj != NULL) {
7110 // Ignore mark word because this could be an already marked oop
7111 // that may be chained at the end of the overflow list.
7112 assert(obj->is_oop(true), "expected an oop");
7113 HeapWord* addr = (HeapWord*)obj;
7114 if (_span.contains(addr) &&
7115 !_bit_map->isMarked(addr)) {
7116 // mark bit map (object will become grey):
7117 // It is possible for several threads to be
7118 // trying to "claim" this object concurrently;
7119 // the unique thread that succeeds in marking the
7120 // object first will do the subsequent push on
7121 // to the work queue (or overflow list).
7122 if (_bit_map->par_mark(addr)) {
7123 // push on work_queue (which may not be empty), and trim the
7124 // queue to an appropriate length by applying this closure to
7125 // the oops in the oops popped from the stack (i.e. blacken the
7126 // grey objects)
7127 bool res = _work_queue->push(obj);
7128 assert(res, "Low water mark should be less than capacity?");
7129 trim_queue(_low_water_mark);
7130 } // Else, another thread claimed the object
7131 }
7132 }
7133 }
7134
7135 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7136 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7137
7138 // This closure is used to rescan the marked objects on the dirty cards
7139 // in the mod union table and the card table proper.
7140 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7141 oop p, MemRegion mr) {
7142
7143 size_t size = 0;
7144 HeapWord* addr = (HeapWord*)p;
7145 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7146 assert(_span.contains(addr), "we are scanning the CMS generation");
7147 // check if it's time to yield
7148 if (do_yield_check()) {
7149 // We yielded for some foreground stop-world work,
7150 // and we have been asked to abort this ongoing preclean cycle.
7151 return 0;
7152 }
7153 if (_bitMap->isMarked(addr)) {
7154 // it's marked; is it potentially uninitialized?
7155 if (p->klass_or_null() != NULL) {
7156 // an initialized object; ignore mark word in verification below
7157 // since we are running concurrent with mutators
7158 assert(p->is_oop(true), "should be an oop");
7159 if (p->is_objArray()) {
7160 // objArrays are precisely marked; restrict scanning
7161 // to dirty cards only.
7162 size = CompactibleFreeListSpace::adjustObjectSize(
7163 p->oop_iterate(_scanningClosure, mr));
7164 } else {
7165 // A non-array may have been imprecisely marked; we need
7166 // to scan object in its entirety.
7167 size = CompactibleFreeListSpace::adjustObjectSize(
7168 p->oop_iterate(_scanningClosure));
7169 }
7170 #ifdef ASSERT
7171 size_t direct_size =
7172 CompactibleFreeListSpace::adjustObjectSize(p->size());
7173 assert(size == direct_size, "Inconsistency in size");
7174 assert(size >= 3, "Necessary for Printezis marks to work");
7175 if (!_bitMap->isMarked(addr+1)) {
7176 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7177 } else {
7178 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7179 assert(_bitMap->isMarked(addr+size-1),
7180 "inconsistent Printezis mark");
7181 }
7182 #endif // ASSERT
7183 } else {
7184 // An uninitialized object.
7185 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7186 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7187 size = pointer_delta(nextOneAddr + 1, addr);
7188 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7189 "alignment problem");
7190 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7191 // will dirty the card when the klass pointer is installed in the
7192 // object (signaling the completion of initialization).
7193 }
7194 } else {
7195 // Either a not yet marked object or an uninitialized object
7196 if (p->klass_or_null() == NULL) {
7197 // An uninitialized object, skip to the next card, since
7198 // we may not be able to read its P-bits yet.
7199 assert(size == 0, "Initial value");
7200 } else {
7201 // An object not (yet) reached by marking: we merely need to
7202 // compute its size so as to go look at the next block.
7203 assert(p->is_oop(true), "should be an oop");
7204 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7205 }
7206 }
7207 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7208 return size;
7209 }
7210
7211 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7212 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7213 "CMS thread should hold CMS token");
7214 assert_lock_strong(_freelistLock);
7215 assert_lock_strong(_bitMap->lock());
7216 // relinquish the free_list_lock and bitMaplock()
7217 _bitMap->lock()->unlock();
7218 _freelistLock->unlock();
7219 ConcurrentMarkSweepThread::desynchronize(true);
7220 ConcurrentMarkSweepThread::acknowledge_yield_request();
7221 _collector->stopTimer();
7222 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7223 if (PrintCMSStatistics != 0) {
7224 _collector->incrementYields();
7225 }
7226 _collector->icms_wait();
7227
7228 // See the comment in coordinator_yield()
7229 for (unsigned i = 0; i < CMSYieldSleepCount &&
7230 ConcurrentMarkSweepThread::should_yield() &&
7231 !CMSCollector::foregroundGCIsActive(); ++i) {
7232 os::sleep(Thread::current(), 1, false);
7233 ConcurrentMarkSweepThread::acknowledge_yield_request();
7234 }
7235
7236 ConcurrentMarkSweepThread::synchronize(true);
7237 _freelistLock->lock_without_safepoint_check();
7238 _bitMap->lock()->lock_without_safepoint_check();
7239 _collector->startTimer();
7240 }
7241
7242
7243 //////////////////////////////////////////////////////////////////
7244 // SurvivorSpacePrecleanClosure
7245 //////////////////////////////////////////////////////////////////
7246 // This (single-threaded) closure is used to preclean the oops in
7247 // the survivor spaces.
7248 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7249
7250 HeapWord* addr = (HeapWord*)p;
7251 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7252 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7253 assert(p->klass_or_null() != NULL, "object should be initialized");
7254 // an initialized object; ignore mark word in verification below
7255 // since we are running concurrent with mutators
7256 assert(p->is_oop(true), "should be an oop");
7257 // Note that we do not yield while we iterate over
7258 // the interior oops of p, pushing the relevant ones
7259 // on our marking stack.
7260 size_t size = p->oop_iterate(_scanning_closure);
7261 do_yield_check();
7262 // Observe that below, we do not abandon the preclean
7263 // phase as soon as we should; rather we empty the
7264 // marking stack before returning. This is to satisfy
7265 // some existing assertions. In general, it may be a
7266 // good idea to abort immediately and complete the marking
7267 // from the grey objects at a later time.
7268 while (!_mark_stack->isEmpty()) {
7269 oop new_oop = _mark_stack->pop();
7270 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7271 assert(_bit_map->isMarked((HeapWord*)new_oop),
7272 "only grey objects on this stack");
7273 // iterate over the oops in this oop, marking and pushing
7274 // the ones in CMS heap (i.e. in _span).
7275 new_oop->oop_iterate(_scanning_closure);
7276 // check if it's time to yield
7277 do_yield_check();
7278 }
7279 unsigned int after_count =
7280 GenCollectedHeap::heap()->total_collections();
7281 bool abort = (_before_count != after_count) ||
7282 _collector->should_abort_preclean();
7283 return abort ? 0 : size;
7284 }
7285
7286 void SurvivorSpacePrecleanClosure::do_yield_work() {
7287 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7288 "CMS thread should hold CMS token");
7289 assert_lock_strong(_bit_map->lock());
7290 // Relinquish the bit map lock
7291 _bit_map->lock()->unlock();
7292 ConcurrentMarkSweepThread::desynchronize(true);
7293 ConcurrentMarkSweepThread::acknowledge_yield_request();
7294 _collector->stopTimer();
7295 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7296 if (PrintCMSStatistics != 0) {
7297 _collector->incrementYields();
7298 }
7299 _collector->icms_wait();
7300
7301 // See the comment in coordinator_yield()
7302 for (unsigned i = 0; i < CMSYieldSleepCount &&
7303 ConcurrentMarkSweepThread::should_yield() &&
7304 !CMSCollector::foregroundGCIsActive(); ++i) {
7305 os::sleep(Thread::current(), 1, false);
7306 ConcurrentMarkSweepThread::acknowledge_yield_request();
7307 }
7308
7309 ConcurrentMarkSweepThread::synchronize(true);
7310 _bit_map->lock()->lock_without_safepoint_check();
7311 _collector->startTimer();
7312 }
7313
7314 // This closure is used to rescan the marked objects on the dirty cards
7315 // in the mod union table and the card table proper. In the parallel
7316 // case, although the bitMap is shared, we do a single read so the
7317 // isMarked() query is "safe".
7318 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7319 // Ignore mark word because we are running concurrent with mutators
7320 assert(p->is_oop_or_null(true), "expected an oop or null");
7321 HeapWord* addr = (HeapWord*)p;
7322 assert(_span.contains(addr), "we are scanning the CMS generation");
7323 bool is_obj_array = false;
7324 #ifdef ASSERT
7325 if (!_parallel) {
7326 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7327 assert(_collector->overflow_list_is_empty(),
7328 "overflow list should be empty");
7329
7330 }
7331 #endif // ASSERT
7332 if (_bit_map->isMarked(addr)) {
7333 // Obj arrays are precisely marked, non-arrays are not;
7334 // so we scan objArrays precisely and non-arrays in their
7335 // entirety.
7336 if (p->is_objArray()) {
7337 is_obj_array = true;
7338 if (_parallel) {
7339 p->oop_iterate(_par_scan_closure, mr);
7340 } else {
7341 p->oop_iterate(_scan_closure, mr);
7342 }
7343 } else {
7344 if (_parallel) {
7345 p->oop_iterate(_par_scan_closure);
7346 } else {
7347 p->oop_iterate(_scan_closure);
7348 }
7349 }
7350 }
7351 #ifdef ASSERT
7352 if (!_parallel) {
7353 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7354 assert(_collector->overflow_list_is_empty(),
7355 "overflow list should be empty");
7356
7357 }
7358 #endif // ASSERT
7359 return is_obj_array;
7360 }
7361
7362 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7363 MemRegion span,
7364 CMSBitMap* bitMap, CMSMarkStack* markStack,
7365 bool should_yield, bool verifying):
7366 _collector(collector),
7367 _span(span),
7368 _bitMap(bitMap),
7369 _mut(&collector->_modUnionTable),
7370 _markStack(markStack),
7371 _yield(should_yield),
7372 _skipBits(0)
7373 {
7374 assert(_markStack->isEmpty(), "stack should be empty");
7375 _finger = _bitMap->startWord();
7376 _threshold = _finger;
7377 assert(_collector->_restart_addr == NULL, "Sanity check");
7378 assert(_span.contains(_finger), "Out of bounds _finger?");
7379 DEBUG_ONLY(_verifying = verifying;)
7380 }
7381
7382 void MarkFromRootsClosure::reset(HeapWord* addr) {
7383 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7384 assert(_span.contains(addr), "Out of bounds _finger?");
7385 _finger = addr;
7386 _threshold = (HeapWord*)round_to(
7387 (intptr_t)_finger, CardTableModRefBS::card_size);
7388 }
7389
7390 // Should revisit to see if this should be restructured for
7391 // greater efficiency.
7392 bool MarkFromRootsClosure::do_bit(size_t offset) {
7393 if (_skipBits > 0) {
7394 _skipBits--;
7395 return true;
7396 }
7397 // convert offset into a HeapWord*
7398 HeapWord* addr = _bitMap->startWord() + offset;
7399 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7400 "address out of range");
7401 assert(_bitMap->isMarked(addr), "tautology");
7402 if (_bitMap->isMarked(addr+1)) {
7403 // this is an allocated but not yet initialized object
7404 assert(_skipBits == 0, "tautology");
7405 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7406 oop p = oop(addr);
7407 if (p->klass_or_null() == NULL) {
7408 DEBUG_ONLY(if (!_verifying) {)
7409 // We re-dirty the cards on which this object lies and increase
7410 // the _threshold so that we'll come back to scan this object
7411 // during the preclean or remark phase. (CMSCleanOnEnter)
7412 if (CMSCleanOnEnter) {
7413 size_t sz = _collector->block_size_using_printezis_bits(addr);
7414 HeapWord* end_card_addr = (HeapWord*)round_to(
7415 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7416 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7417 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7418 // Bump _threshold to end_card_addr; note that
7419 // _threshold cannot possibly exceed end_card_addr, anyhow.
7420 // This prevents future clearing of the card as the scan proceeds
7421 // to the right.
7422 assert(_threshold <= end_card_addr,
7423 "Because we are just scanning into this object");
7424 if (_threshold < end_card_addr) {
7425 _threshold = end_card_addr;
7426 }
7427 if (p->klass_or_null() != NULL) {
7428 // Redirty the range of cards...
7429 _mut->mark_range(redirty_range);
7430 } // ...else the setting of klass will dirty the card anyway.
7431 }
7432 DEBUG_ONLY(})
7433 return true;
7434 }
7435 }
7436 scanOopsInOop(addr);
7437 return true;
7438 }
7439
7440 // We take a break if we've been at this for a while,
7441 // so as to avoid monopolizing the locks involved.
7442 void MarkFromRootsClosure::do_yield_work() {
7443 // First give up the locks, then yield, then re-lock
7444 // We should probably use a constructor/destructor idiom to
7445 // do this unlock/lock or modify the MutexUnlocker class to
7446 // serve our purpose. XXX
7447 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7448 "CMS thread should hold CMS token");
7449 assert_lock_strong(_bitMap->lock());
7450 _bitMap->lock()->unlock();
7451 ConcurrentMarkSweepThread::desynchronize(true);
7452 ConcurrentMarkSweepThread::acknowledge_yield_request();
7453 _collector->stopTimer();
7454 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7455 if (PrintCMSStatistics != 0) {
7456 _collector->incrementYields();
7457 }
7458 _collector->icms_wait();
7459
7460 // See the comment in coordinator_yield()
7461 for (unsigned i = 0; i < CMSYieldSleepCount &&
7462 ConcurrentMarkSweepThread::should_yield() &&
7463 !CMSCollector::foregroundGCIsActive(); ++i) {
7464 os::sleep(Thread::current(), 1, false);
7465 ConcurrentMarkSweepThread::acknowledge_yield_request();
7466 }
7467
7468 ConcurrentMarkSweepThread::synchronize(true);
7469 _bitMap->lock()->lock_without_safepoint_check();
7470 _collector->startTimer();
7471 }
7472
7473 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7474 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7475 assert(_markStack->isEmpty(),
7476 "should drain stack to limit stack usage");
7477 // convert ptr to an oop preparatory to scanning
7478 oop obj = oop(ptr);
7479 // Ignore mark word in verification below, since we
7480 // may be running concurrent with mutators.
7481 assert(obj->is_oop(true), "should be an oop");
7482 assert(_finger <= ptr, "_finger runneth ahead");
7483 // advance the finger to right end of this object
7484 _finger = ptr + obj->size();
7485 assert(_finger > ptr, "we just incremented it above");
7486 // On large heaps, it may take us some time to get through
7487 // the marking phase (especially if running iCMS). During
7488 // this time it's possible that a lot of mutations have
7489 // accumulated in the card table and the mod union table --
7490 // these mutation records are redundant until we have
7491 // actually traced into the corresponding card.
7492 // Here, we check whether advancing the finger would make
7493 // us cross into a new card, and if so clear corresponding
7494 // cards in the MUT (preclean them in the card-table in the
7495 // future).
7496
7497 DEBUG_ONLY(if (!_verifying) {)
7498 // The clean-on-enter optimization is disabled by default,
7499 // until we fix 6178663.
7500 if (CMSCleanOnEnter && (_finger > _threshold)) {
7501 // [_threshold, _finger) represents the interval
7502 // of cards to be cleared in MUT (or precleaned in card table).
7503 // The set of cards to be cleared is all those that overlap
7504 // with the interval [_threshold, _finger); note that
7505 // _threshold is always kept card-aligned but _finger isn't
7506 // always card-aligned.
7507 HeapWord* old_threshold = _threshold;
7508 assert(old_threshold == (HeapWord*)round_to(
7509 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7510 "_threshold should always be card-aligned");
7511 _threshold = (HeapWord*)round_to(
7512 (intptr_t)_finger, CardTableModRefBS::card_size);
7513 MemRegion mr(old_threshold, _threshold);
7514 assert(!mr.is_empty(), "Control point invariant");
7515 assert(_span.contains(mr), "Should clear within span");
7516 _mut->clear_range(mr);
7517 }
7518 DEBUG_ONLY(})
7519 // Note: the finger doesn't advance while we drain
7520 // the stack below.
7521 PushOrMarkClosure pushOrMarkClosure(_collector,
7522 _span, _bitMap, _markStack,
7523 _finger, this);
7524 bool res = _markStack->push(obj);
7525 assert(res, "Empty non-zero size stack should have space for single push");
7526 while (!_markStack->isEmpty()) {
7527 oop new_oop = _markStack->pop();
7528 // Skip verifying header mark word below because we are
7529 // running concurrent with mutators.
7530 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7531 // now scan this oop's oops
7532 new_oop->oop_iterate(&pushOrMarkClosure);
7533 do_yield_check();
7534 }
7535 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7536 }
7537
7538 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7539 CMSCollector* collector, MemRegion span,
7540 CMSBitMap* bit_map,
7541 OopTaskQueue* work_queue,
7542 CMSMarkStack* overflow_stack,
7543 bool should_yield):
7544 _collector(collector),
7545 _whole_span(collector->_span),
7546 _span(span),
7547 _bit_map(bit_map),
7548 _mut(&collector->_modUnionTable),
7549 _work_queue(work_queue),
7550 _overflow_stack(overflow_stack),
7551 _yield(should_yield),
7552 _skip_bits(0),
7553 _task(task)
7554 {
7555 assert(_work_queue->size() == 0, "work_queue should be empty");
7556 _finger = span.start();
7557 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7558 assert(_span.contains(_finger), "Out of bounds _finger?");
7559 }
7560
7561 // Should revisit to see if this should be restructured for
7562 // greater efficiency.
7563 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7564 if (_skip_bits > 0) {
7565 _skip_bits--;
7566 return true;
7567 }
7568 // convert offset into a HeapWord*
7569 HeapWord* addr = _bit_map->startWord() + offset;
7570 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7571 "address out of range");
7572 assert(_bit_map->isMarked(addr), "tautology");
7573 if (_bit_map->isMarked(addr+1)) {
7574 // this is an allocated object that might not yet be initialized
7575 assert(_skip_bits == 0, "tautology");
7576 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7577 oop p = oop(addr);
7578 if (p->klass_or_null() == NULL) {
7579 // in the case of Clean-on-Enter optimization, redirty card
7580 // and avoid clearing card by increasing the threshold.
7581 return true;
7582 }
7583 }
7584 scan_oops_in_oop(addr);
7585 return true;
7586 }
7587
7588 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7589 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7590 // Should we assert that our work queue is empty or
7591 // below some drain limit?
7592 assert(_work_queue->size() == 0,
7593 "should drain stack to limit stack usage");
7594 // convert ptr to an oop preparatory to scanning
7595 oop obj = oop(ptr);
7596 // Ignore mark word in verification below, since we
7597 // may be running concurrent with mutators.
7598 assert(obj->is_oop(true), "should be an oop");
7599 assert(_finger <= ptr, "_finger runneth ahead");
7600 // advance the finger to right end of this object
7601 _finger = ptr + obj->size();
7602 assert(_finger > ptr, "we just incremented it above");
7603 // On large heaps, it may take us some time to get through
7604 // the marking phase (especially if running iCMS). During
7605 // this time it's possible that a lot of mutations have
7606 // accumulated in the card table and the mod union table --
7607 // these mutation records are redundant until we have
7608 // actually traced into the corresponding card.
7609 // Here, we check whether advancing the finger would make
7610 // us cross into a new card, and if so clear corresponding
7611 // cards in the MUT (preclean them in the card-table in the
7612 // future).
7613
7614 // The clean-on-enter optimization is disabled by default,
7615 // until we fix 6178663.
7616 if (CMSCleanOnEnter && (_finger > _threshold)) {
7617 // [_threshold, _finger) represents the interval
7618 // of cards to be cleared in MUT (or precleaned in card table).
7619 // The set of cards to be cleared is all those that overlap
7620 // with the interval [_threshold, _finger); note that
7621 // _threshold is always kept card-aligned but _finger isn't
7622 // always card-aligned.
7623 HeapWord* old_threshold = _threshold;
7624 assert(old_threshold == (HeapWord*)round_to(
7625 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7626 "_threshold should always be card-aligned");
7627 _threshold = (HeapWord*)round_to(
7628 (intptr_t)_finger, CardTableModRefBS::card_size);
7629 MemRegion mr(old_threshold, _threshold);
7630 assert(!mr.is_empty(), "Control point invariant");
7631 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7632 _mut->clear_range(mr);
7633 }
7634
7635 // Note: the local finger doesn't advance while we drain
7636 // the stack below, but the global finger sure can and will.
7637 HeapWord** gfa = _task->global_finger_addr();
7638 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7639 _span, _bit_map,
7640 _work_queue,
7641 _overflow_stack,
7642 _finger,
7643 gfa, this);
7644 bool res = _work_queue->push(obj); // overflow could occur here
7645 assert(res, "Will hold once we use workqueues");
7646 while (true) {
7647 oop new_oop;
7648 if (!_work_queue->pop_local(new_oop)) {
7649 // We emptied our work_queue; check if there's stuff that can
7650 // be gotten from the overflow stack.
7651 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7652 _overflow_stack, _work_queue)) {
7653 do_yield_check();
7654 continue;
7655 } else { // done
7656 break;
7657 }
7658 }
7659 // Skip verifying header mark word below because we are
7660 // running concurrent with mutators.
7661 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7662 // now scan this oop's oops
7663 new_oop->oop_iterate(&pushOrMarkClosure);
7664 do_yield_check();
7665 }
7666 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7667 }
7668
7669 // Yield in response to a request from VM Thread or
7670 // from mutators.
7671 void Par_MarkFromRootsClosure::do_yield_work() {
7672 assert(_task != NULL, "sanity");
7673 _task->yield();
7674 }
7675
7676 // A variant of the above used for verifying CMS marking work.
7677 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7678 MemRegion span,
7679 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7680 CMSMarkStack* mark_stack):
7681 _collector(collector),
7682 _span(span),
7683 _verification_bm(verification_bm),
7684 _cms_bm(cms_bm),
7685 _mark_stack(mark_stack),
7686 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7687 mark_stack)
7688 {
7689 assert(_mark_stack->isEmpty(), "stack should be empty");
7690 _finger = _verification_bm->startWord();
7691 assert(_collector->_restart_addr == NULL, "Sanity check");
7692 assert(_span.contains(_finger), "Out of bounds _finger?");
7693 }
7694
7695 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7696 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7697 assert(_span.contains(addr), "Out of bounds _finger?");
7698 _finger = addr;
7699 }
7700
7701 // Should revisit to see if this should be restructured for
7702 // greater efficiency.
7703 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7704 // convert offset into a HeapWord*
7705 HeapWord* addr = _verification_bm->startWord() + offset;
7706 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7707 "address out of range");
7708 assert(_verification_bm->isMarked(addr), "tautology");
7709 assert(_cms_bm->isMarked(addr), "tautology");
7710
7711 assert(_mark_stack->isEmpty(),
7712 "should drain stack to limit stack usage");
7713 // convert addr to an oop preparatory to scanning
7714 oop obj = oop(addr);
7715 assert(obj->is_oop(), "should be an oop");
7716 assert(_finger <= addr, "_finger runneth ahead");
7717 // advance the finger to right end of this object
7718 _finger = addr + obj->size();
7719 assert(_finger > addr, "we just incremented it above");
7720 // Note: the finger doesn't advance while we drain
7721 // the stack below.
7722 bool res = _mark_stack->push(obj);
7723 assert(res, "Empty non-zero size stack should have space for single push");
7724 while (!_mark_stack->isEmpty()) {
7725 oop new_oop = _mark_stack->pop();
7726 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7727 // now scan this oop's oops
7728 new_oop->oop_iterate(&_pam_verify_closure);
7729 }
7730 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7731 return true;
7732 }
7733
7734 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7735 CMSCollector* collector, MemRegion span,
7736 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7737 CMSMarkStack* mark_stack):
7738 CMSOopClosure(collector->ref_processor()),
7739 _collector(collector),
7740 _span(span),
7741 _verification_bm(verification_bm),
7742 _cms_bm(cms_bm),
7743 _mark_stack(mark_stack)
7744 { }
7745
7746 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7747 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7748
7749 // Upon stack overflow, we discard (part of) the stack,
7750 // remembering the least address amongst those discarded
7751 // in CMSCollector's _restart_address.
7752 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7753 // Remember the least grey address discarded
7754 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7755 _collector->lower_restart_addr(ra);
7756 _mark_stack->reset(); // discard stack contents
7757 _mark_stack->expand(); // expand the stack if possible
7758 }
7759
7760 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7761 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7762 HeapWord* addr = (HeapWord*)obj;
7763 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7764 // Oop lies in _span and isn't yet grey or black
7765 _verification_bm->mark(addr); // now grey
7766 if (!_cms_bm->isMarked(addr)) {
7767 oop(addr)->print();
7768 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7769 addr);
7770 fatal("... aborting");
7771 }
7772
7773 if (!_mark_stack->push(obj)) { // stack overflow
7774 if (PrintCMSStatistics != 0) {
7775 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7776 SIZE_FORMAT, _mark_stack->capacity());
7777 }
7778 assert(_mark_stack->isFull(), "Else push should have succeeded");
7779 handle_stack_overflow(addr);
7780 }
7781 // anything including and to the right of _finger
7782 // will be scanned as we iterate over the remainder of the
7783 // bit map
7784 }
7785 }
7786
7787 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7788 MemRegion span,
7789 CMSBitMap* bitMap, CMSMarkStack* markStack,
7790 HeapWord* finger, MarkFromRootsClosure* parent) :
7791 CMSOopClosure(collector->ref_processor()),
7792 _collector(collector),
7793 _span(span),
7794 _bitMap(bitMap),
7795 _markStack(markStack),
7796 _finger(finger),
7797 _parent(parent)
7798 { }
7799
7800 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7801 MemRegion span,
7802 CMSBitMap* bit_map,
7803 OopTaskQueue* work_queue,
7804 CMSMarkStack* overflow_stack,
7805 HeapWord* finger,
7806 HeapWord** global_finger_addr,
7807 Par_MarkFromRootsClosure* parent) :
7808 CMSOopClosure(collector->ref_processor()),
7809 _collector(collector),
7810 _whole_span(collector->_span),
7811 _span(span),
7812 _bit_map(bit_map),
7813 _work_queue(work_queue),
7814 _overflow_stack(overflow_stack),
7815 _finger(finger),
7816 _global_finger_addr(global_finger_addr),
7817 _parent(parent)
7818 { }
7819
7820 // Assumes thread-safe access by callers, who are
7821 // responsible for mutual exclusion.
7822 void CMSCollector::lower_restart_addr(HeapWord* low) {
7823 assert(_span.contains(low), "Out of bounds addr");
7824 if (_restart_addr == NULL) {
7825 _restart_addr = low;
7826 } else {
7827 _restart_addr = MIN2(_restart_addr, low);
7828 }
7829 }
7830
7831 // Upon stack overflow, we discard (part of) the stack,
7832 // remembering the least address amongst those discarded
7833 // in CMSCollector's _restart_address.
7834 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7835 // Remember the least grey address discarded
7836 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7837 _collector->lower_restart_addr(ra);
7838 _markStack->reset(); // discard stack contents
7839 _markStack->expand(); // expand the stack if possible
7840 }
7841
7842 // Upon stack overflow, we discard (part of) the stack,
7843 // remembering the least address amongst those discarded
7844 // in CMSCollector's _restart_address.
7845 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7846 // We need to do this under a mutex to prevent other
7847 // workers from interfering with the work done below.
7848 MutexLockerEx ml(_overflow_stack->par_lock(),
7849 Mutex::_no_safepoint_check_flag);
7850 // Remember the least grey address discarded
7851 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7852 _collector->lower_restart_addr(ra);
7853 _overflow_stack->reset(); // discard stack contents
7854 _overflow_stack->expand(); // expand the stack if possible
7855 }
7856
7857 void CMKlassClosure::do_klass(Klass* k) {
7858 assert(_oop_closure != NULL, "Not initialized?");
7859 k->oops_do(_oop_closure);
7860 }
7861
7862 void PushOrMarkClosure::do_oop(oop obj) {
7863 // Ignore mark word because we are running concurrent with mutators.
7864 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7865 HeapWord* addr = (HeapWord*)obj;
7866 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7867 // Oop lies in _span and isn't yet grey or black
7868 _bitMap->mark(addr); // now grey
7869 if (addr < _finger) {
7870 // the bit map iteration has already either passed, or
7871 // sampled, this bit in the bit map; we'll need to
7872 // use the marking stack to scan this oop's oops.
7873 bool simulate_overflow = false;
7874 NOT_PRODUCT(
7875 if (CMSMarkStackOverflowALot &&
7876 _collector->simulate_overflow()) {
7877 // simulate a stack overflow
7878 simulate_overflow = true;
7879 }
7880 )
7881 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7882 if (PrintCMSStatistics != 0) {
7883 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7884 SIZE_FORMAT, _markStack->capacity());
7885 }
7886 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7887 handle_stack_overflow(addr);
7888 }
7889 }
7890 // anything including and to the right of _finger
7891 // will be scanned as we iterate over the remainder of the
7892 // bit map
7893 do_yield_check();
7894 }
7895 }
7896
7897 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7898 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7899
7900 void Par_PushOrMarkClosure::do_oop(oop obj) {
7901 // Ignore mark word because we are running concurrent with mutators.
7902 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7903 HeapWord* addr = (HeapWord*)obj;
7904 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7905 // Oop lies in _span and isn't yet grey or black
7906 // We read the global_finger (volatile read) strictly after marking oop
7907 bool res = _bit_map->par_mark(addr); // now grey
7908 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7909 // Should we push this marked oop on our stack?
7910 // -- if someone else marked it, nothing to do
7911 // -- if target oop is above global finger nothing to do
7912 // -- if target oop is in chunk and above local finger
7913 // then nothing to do
7914 // -- else push on work queue
7915 if ( !res // someone else marked it, they will deal with it
7916 || (addr >= *gfa) // will be scanned in a later task
7917 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7918 return;
7919 }
7920 // the bit map iteration has already either passed, or
7921 // sampled, this bit in the bit map; we'll need to
7922 // use the marking stack to scan this oop's oops.
7923 bool simulate_overflow = false;
7924 NOT_PRODUCT(
7925 if (CMSMarkStackOverflowALot &&
7926 _collector->simulate_overflow()) {
7927 // simulate a stack overflow
7928 simulate_overflow = true;
7929 }
7930 )
7931 if (simulate_overflow ||
7932 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7933 // stack overflow
7934 if (PrintCMSStatistics != 0) {
7935 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7936 SIZE_FORMAT, _overflow_stack->capacity());
7937 }
7938 // We cannot assert that the overflow stack is full because
7939 // it may have been emptied since.
7940 assert(simulate_overflow ||
7941 _work_queue->size() == _work_queue->max_elems(),
7942 "Else push should have succeeded");
7943 handle_stack_overflow(addr);
7944 }
7945 do_yield_check();
7946 }
7947 }
7948
7949 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7950 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7951
7952 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7953 MemRegion span,
7954 ReferenceProcessor* rp,
7955 CMSBitMap* bit_map,
7956 CMSBitMap* mod_union_table,
7957 CMSMarkStack* mark_stack,
7958 bool concurrent_precleaning):
7959 CMSOopClosure(rp),
7960 _collector(collector),
7961 _span(span),
7962 _bit_map(bit_map),
7963 _mod_union_table(mod_union_table),
7964 _mark_stack(mark_stack),
7965 _concurrent_precleaning(concurrent_precleaning)
7966 {
7967 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7968 }
7969
7970 // Grey object rescan during pre-cleaning and second checkpoint phases --
7971 // the non-parallel version (the parallel version appears further below.)
7972 void PushAndMarkClosure::do_oop(oop obj) {
7973 // Ignore mark word verification. If during concurrent precleaning,
7974 // the object monitor may be locked. If during the checkpoint
7975 // phases, the object may already have been reached by a different
7976 // path and may be at the end of the global overflow list (so
7977 // the mark word may be NULL).
7978 assert(obj->is_oop_or_null(true /* ignore mark word */),
7979 "expected an oop or NULL");
7980 HeapWord* addr = (HeapWord*)obj;
7981 // Check if oop points into the CMS generation
7982 // and is not marked
7983 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7984 // a white object ...
7985 _bit_map->mark(addr); // ... now grey
7986 // push on the marking stack (grey set)
7987 bool simulate_overflow = false;
7988 NOT_PRODUCT(
7989 if (CMSMarkStackOverflowALot &&
7990 _collector->simulate_overflow()) {
7991 // simulate a stack overflow
7992 simulate_overflow = true;
7993 }
7994 )
7995 if (simulate_overflow || !_mark_stack->push(obj)) {
7996 if (_concurrent_precleaning) {
7997 // During precleaning we can just dirty the appropriate card(s)
7998 // in the mod union table, thus ensuring that the object remains
7999 // in the grey set and continue. In the case of object arrays
8000 // we need to dirty all of the cards that the object spans,
8001 // since the rescan of object arrays will be limited to the
8002 // dirty cards.
8003 // Note that no one can be interfering with us in this action
8004 // of dirtying the mod union table, so no locking or atomics
8005 // are required.
8006 if (obj->is_objArray()) {
8007 size_t sz = obj->size();
8008 HeapWord* end_card_addr = (HeapWord*)round_to(
8009 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
8010 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8011 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8012 _mod_union_table->mark_range(redirty_range);
8013 } else {
8014 _mod_union_table->mark(addr);
8015 }
8016 _collector->_ser_pmc_preclean_ovflw++;
8017 } else {
8018 // During the remark phase, we need to remember this oop
8019 // in the overflow list.
8020 _collector->push_on_overflow_list(obj);
8021 _collector->_ser_pmc_remark_ovflw++;
8022 }
8023 }
8024 }
8025 }
8026
8027 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8028 MemRegion span,
8029 ReferenceProcessor* rp,
8030 CMSBitMap* bit_map,
8031 OopTaskQueue* work_queue):
8032 CMSOopClosure(rp),
8033 _collector(collector),
8034 _span(span),
8035 _bit_map(bit_map),
8036 _work_queue(work_queue)
8037 {
8038 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8039 }
8040
8041 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8042 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8043
8044 // Grey object rescan during second checkpoint phase --
8045 // the parallel version.
8046 void Par_PushAndMarkClosure::do_oop(oop obj) {
8047 // In the assert below, we ignore the mark word because
8048 // this oop may point to an already visited object that is
8049 // on the overflow stack (in which case the mark word has
8050 // been hijacked for chaining into the overflow stack --
8051 // if this is the last object in the overflow stack then
8052 // its mark word will be NULL). Because this object may
8053 // have been subsequently popped off the global overflow
8054 // stack, and the mark word possibly restored to the prototypical
8055 // value, by the time we get to examined this failing assert in
8056 // the debugger, is_oop_or_null(false) may subsequently start
8057 // to hold.
8058 assert(obj->is_oop_or_null(true),
8059 "expected an oop or NULL");
8060 HeapWord* addr = (HeapWord*)obj;
8061 // Check if oop points into the CMS generation
8062 // and is not marked
8063 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8064 // a white object ...
8065 // If we manage to "claim" the object, by being the
8066 // first thread to mark it, then we push it on our
8067 // marking stack
8068 if (_bit_map->par_mark(addr)) { // ... now grey
8069 // push on work queue (grey set)
8070 bool simulate_overflow = false;
8071 NOT_PRODUCT(
8072 if (CMSMarkStackOverflowALot &&
8073 _collector->par_simulate_overflow()) {
8074 // simulate a stack overflow
8075 simulate_overflow = true;
8076 }
8077 )
8078 if (simulate_overflow || !_work_queue->push(obj)) {
8079 _collector->par_push_on_overflow_list(obj);
8080 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8081 }
8082 } // Else, some other thread got there first
8083 }
8084 }
8085
8086 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8087 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8088
8089 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8090 Mutex* bml = _collector->bitMapLock();
8091 assert_lock_strong(bml);
8092 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8093 "CMS thread should hold CMS token");
8094
8095 bml->unlock();
8096 ConcurrentMarkSweepThread::desynchronize(true);
8097
8098 ConcurrentMarkSweepThread::acknowledge_yield_request();
8099
8100 _collector->stopTimer();
8101 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8102 if (PrintCMSStatistics != 0) {
8103 _collector->incrementYields();
8104 }
8105 _collector->icms_wait();
8106
8107 // See the comment in coordinator_yield()
8108 for (unsigned i = 0; i < CMSYieldSleepCount &&
8109 ConcurrentMarkSweepThread::should_yield() &&
8110 !CMSCollector::foregroundGCIsActive(); ++i) {
8111 os::sleep(Thread::current(), 1, false);
8112 ConcurrentMarkSweepThread::acknowledge_yield_request();
8113 }
8114
8115 ConcurrentMarkSweepThread::synchronize(true);
8116 bml->lock();
8117
8118 _collector->startTimer();
8119 }
8120
8121 bool CMSPrecleanRefsYieldClosure::should_return() {
8122 if (ConcurrentMarkSweepThread::should_yield()) {
8123 do_yield_work();
8124 }
8125 return _collector->foregroundGCIsActive();
8126 }
8127
8128 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8129 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8130 "mr should be aligned to start at a card boundary");
8131 // We'd like to assert:
8132 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8133 // "mr should be a range of cards");
8134 // However, that would be too strong in one case -- the last
8135 // partition ends at _unallocated_block which, in general, can be
8136 // an arbitrary boundary, not necessarily card aligned.
8137 if (PrintCMSStatistics != 0) {
8138 _num_dirty_cards +=
8139 mr.word_size()/CardTableModRefBS::card_size_in_words;
8140 }
8141 _space->object_iterate_mem(mr, &_scan_cl);
8142 }
8143
8144 SweepClosure::SweepClosure(CMSCollector* collector,
8145 ConcurrentMarkSweepGeneration* g,
8146 CMSBitMap* bitMap, bool should_yield) :
8147 _collector(collector),
8148 _g(g),
8149 _sp(g->cmsSpace()),
8150 _limit(_sp->sweep_limit()),
8151 _freelistLock(_sp->freelistLock()),
8152 _bitMap(bitMap),
8153 _yield(should_yield),
8154 _inFreeRange(false), // No free range at beginning of sweep
8155 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8156 _lastFreeRangeCoalesced(false),
8157 _freeFinger(g->used_region().start())
8158 {
8159 NOT_PRODUCT(
8160 _numObjectsFreed = 0;
8161 _numWordsFreed = 0;
8162 _numObjectsLive = 0;
8163 _numWordsLive = 0;
8164 _numObjectsAlreadyFree = 0;
8165 _numWordsAlreadyFree = 0;
8166 _last_fc = NULL;
8167
8168 _sp->initializeIndexedFreeListArrayReturnedBytes();
8169 _sp->dictionary()->initialize_dict_returned_bytes();
8170 )
8171 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8172 "sweep _limit out of bounds");
8173 if (CMSTraceSweeper) {
8174 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8175 _limit);
8176 }
8177 }
8178
8179 void SweepClosure::print_on(outputStream* st) const {
8180 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8181 _sp->bottom(), _sp->end());
8182 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8183 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8184 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8185 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8186 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8187 }
8188
8189 #ifndef PRODUCT
8190 // Assertion checking only: no useful work in product mode --
8191 // however, if any of the flags below become product flags,
8192 // you may need to review this code to see if it needs to be
8193 // enabled in product mode.
8194 SweepClosure::~SweepClosure() {
8195 assert_lock_strong(_freelistLock);
8196 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8197 "sweep _limit out of bounds");
8198 if (inFreeRange()) {
8199 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8200 print();
8201 ShouldNotReachHere();
8202 }
8203 if (Verbose && PrintGC) {
8204 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8205 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8206 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8207 SIZE_FORMAT" bytes "
8208 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8209 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8210 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8211 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8212 * sizeof(HeapWord);
8213 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8214
8215 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8216 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8217 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8218 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8219 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8220 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8221 indexListReturnedBytes);
8222 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8223 dict_returned_bytes);
8224 }
8225 }
8226 if (CMSTraceSweeper) {
8227 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8228 _limit);
8229 }
8230 }
8231 #endif // PRODUCT
8232
8233 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8234 bool freeRangeInFreeLists) {
8235 if (CMSTraceSweeper) {
8236 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
8237 freeFinger, freeRangeInFreeLists);
8238 }
8239 assert(!inFreeRange(), "Trampling existing free range");
8240 set_inFreeRange(true);
8241 set_lastFreeRangeCoalesced(false);
8242
8243 set_freeFinger(freeFinger);
8244 set_freeRangeInFreeLists(freeRangeInFreeLists);
8245 if (CMSTestInFreeList) {
8246 if (freeRangeInFreeLists) {
8247 FreeChunk* fc = (FreeChunk*) freeFinger;
8248 assert(fc->is_free(), "A chunk on the free list should be free.");
8249 assert(fc->size() > 0, "Free range should have a size");
8250 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8251 }
8252 }
8253 }
8254
8255 // Note that the sweeper runs concurrently with mutators. Thus,
8256 // it is possible for direct allocation in this generation to happen
8257 // in the middle of the sweep. Note that the sweeper also coalesces
8258 // contiguous free blocks. Thus, unless the sweeper and the allocator
8259 // synchronize appropriately freshly allocated blocks may get swept up.
8260 // This is accomplished by the sweeper locking the free lists while
8261 // it is sweeping. Thus blocks that are determined to be free are
8262 // indeed free. There is however one additional complication:
8263 // blocks that have been allocated since the final checkpoint and
8264 // mark, will not have been marked and so would be treated as
8265 // unreachable and swept up. To prevent this, the allocator marks
8266 // the bit map when allocating during the sweep phase. This leads,
8267 // however, to a further complication -- objects may have been allocated
8268 // but not yet initialized -- in the sense that the header isn't yet
8269 // installed. The sweeper can not then determine the size of the block
8270 // in order to skip over it. To deal with this case, we use a technique
8271 // (due to Printezis) to encode such uninitialized block sizes in the
8272 // bit map. Since the bit map uses a bit per every HeapWord, but the
8273 // CMS generation has a minimum object size of 3 HeapWords, it follows
8274 // that "normal marks" won't be adjacent in the bit map (there will
8275 // always be at least two 0 bits between successive 1 bits). We make use
8276 // of these "unused" bits to represent uninitialized blocks -- the bit
8277 // corresponding to the start of the uninitialized object and the next
8278 // bit are both set. Finally, a 1 bit marks the end of the object that
8279 // started with the two consecutive 1 bits to indicate its potentially
8280 // uninitialized state.
8281
8282 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8283 FreeChunk* fc = (FreeChunk*)addr;
8284 size_t res;
8285
8286 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8287 // than "addr == _limit" because although _limit was a block boundary when
8288 // we started the sweep, it may no longer be one because heap expansion
8289 // may have caused us to coalesce the block ending at the address _limit
8290 // with a newly expanded chunk (this happens when _limit was set to the
8291 // previous _end of the space), so we may have stepped past _limit:
8292 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8293 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8294 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8295 "sweep _limit out of bounds");
8296 assert(addr < _sp->end(), "addr out of bounds");
8297 // Flush any free range we might be holding as a single
8298 // coalesced chunk to the appropriate free list.
8299 if (inFreeRange()) {
8300 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8301 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8302 flush_cur_free_chunk(freeFinger(),
8303 pointer_delta(addr, freeFinger()));
8304 if (CMSTraceSweeper) {
8305 gclog_or_tty->print("Sweep: last chunk: ");
8306 gclog_or_tty->print("put_free_blk " PTR_FORMAT " ("SIZE_FORMAT") "
8307 "[coalesced:%d]\n",
8308 freeFinger(), pointer_delta(addr, freeFinger()),
8309 lastFreeRangeCoalesced() ? 1 : 0);
8310 }
8311 }
8312
8313 // help the iterator loop finish
8314 return pointer_delta(_sp->end(), addr);
8315 }
8316
8317 assert(addr < _limit, "sweep invariant");
8318 // check if we should yield
8319 do_yield_check(addr);
8320 if (fc->is_free()) {
8321 // Chunk that is already free
8322 res = fc->size();
8323 do_already_free_chunk(fc);
8324 debug_only(_sp->verifyFreeLists());
8325 // If we flush the chunk at hand in lookahead_and_flush()
8326 // and it's coalesced with a preceding chunk, then the
8327 // process of "mangling" the payload of the coalesced block
8328 // will cause erasure of the size information from the
8329 // (erstwhile) header of all the coalesced blocks but the
8330 // first, so the first disjunct in the assert will not hold
8331 // in that specific case (in which case the second disjunct
8332 // will hold).
8333 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8334 "Otherwise the size info doesn't change at this step");
8335 NOT_PRODUCT(
8336 _numObjectsAlreadyFree++;
8337 _numWordsAlreadyFree += res;
8338 )
8339 NOT_PRODUCT(_last_fc = fc;)
8340 } else if (!_bitMap->isMarked(addr)) {
8341 // Chunk is fresh garbage
8342 res = do_garbage_chunk(fc);
8343 debug_only(_sp->verifyFreeLists());
8344 NOT_PRODUCT(
8345 _numObjectsFreed++;
8346 _numWordsFreed += res;
8347 )
8348 } else {
8349 // Chunk that is alive.
8350 res = do_live_chunk(fc);
8351 debug_only(_sp->verifyFreeLists());
8352 NOT_PRODUCT(
8353 _numObjectsLive++;
8354 _numWordsLive += res;
8355 )
8356 }
8357 return res;
8358 }
8359
8360 // For the smart allocation, record following
8361 // split deaths - a free chunk is removed from its free list because
8362 // it is being split into two or more chunks.
8363 // split birth - a free chunk is being added to its free list because
8364 // a larger free chunk has been split and resulted in this free chunk.
8365 // coal death - a free chunk is being removed from its free list because
8366 // it is being coalesced into a large free chunk.
8367 // coal birth - a free chunk is being added to its free list because
8368 // it was created when two or more free chunks where coalesced into
8369 // this free chunk.
8370 //
8371 // These statistics are used to determine the desired number of free
8372 // chunks of a given size. The desired number is chosen to be relative
8373 // to the end of a CMS sweep. The desired number at the end of a sweep
8374 // is the
8375 // count-at-end-of-previous-sweep (an amount that was enough)
8376 // - count-at-beginning-of-current-sweep (the excess)
8377 // + split-births (gains in this size during interval)
8378 // - split-deaths (demands on this size during interval)
8379 // where the interval is from the end of one sweep to the end of the
8380 // next.
8381 //
8382 // When sweeping the sweeper maintains an accumulated chunk which is
8383 // the chunk that is made up of chunks that have been coalesced. That
8384 // will be termed the left-hand chunk. A new chunk of garbage that
8385 // is being considered for coalescing will be referred to as the
8386 // right-hand chunk.
8387 //
8388 // When making a decision on whether to coalesce a right-hand chunk with
8389 // the current left-hand chunk, the current count vs. the desired count
8390 // of the left-hand chunk is considered. Also if the right-hand chunk
8391 // is near the large chunk at the end of the heap (see
8392 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8393 // left-hand chunk is coalesced.
8394 //
8395 // When making a decision about whether to split a chunk, the desired count
8396 // vs. the current count of the candidate to be split is also considered.
8397 // If the candidate is underpopulated (currently fewer chunks than desired)
8398 // a chunk of an overpopulated (currently more chunks than desired) size may
8399 // be chosen. The "hint" associated with a free list, if non-null, points
8400 // to a free list which may be overpopulated.
8401 //
8402
8403 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8404 const size_t size = fc->size();
8405 // Chunks that cannot be coalesced are not in the
8406 // free lists.
8407 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8408 assert(_sp->verify_chunk_in_free_list(fc),
8409 "free chunk should be in free lists");
8410 }
8411 // a chunk that is already free, should not have been
8412 // marked in the bit map
8413 HeapWord* const addr = (HeapWord*) fc;
8414 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8415 // Verify that the bit map has no bits marked between
8416 // addr and purported end of this block.
8417 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8418
8419 // Some chunks cannot be coalesced under any circumstances.
8420 // See the definition of cantCoalesce().
8421 if (!fc->cantCoalesce()) {
8422 // This chunk can potentially be coalesced.
8423 if (_sp->adaptive_freelists()) {
8424 // All the work is done in
8425 do_post_free_or_garbage_chunk(fc, size);
8426 } else { // Not adaptive free lists
8427 // this is a free chunk that can potentially be coalesced by the sweeper;
8428 if (!inFreeRange()) {
8429 // if the next chunk is a free block that can't be coalesced
8430 // it doesn't make sense to remove this chunk from the free lists
8431 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8432 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8433 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8434 nextChunk->is_free() && // ... which is free...
8435 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8436 // nothing to do
8437 } else {
8438 // Potentially the start of a new free range:
8439 // Don't eagerly remove it from the free lists.
8440 // No need to remove it if it will just be put
8441 // back again. (Also from a pragmatic point of view
8442 // if it is a free block in a region that is beyond
8443 // any allocated blocks, an assertion will fail)
8444 // Remember the start of a free run.
8445 initialize_free_range(addr, true);
8446 // end - can coalesce with next chunk
8447 }
8448 } else {
8449 // the midst of a free range, we are coalescing
8450 print_free_block_coalesced(fc);
8451 if (CMSTraceSweeper) {
8452 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8453 }
8454 // remove it from the free lists
8455 _sp->removeFreeChunkFromFreeLists(fc);
8456 set_lastFreeRangeCoalesced(true);
8457 // If the chunk is being coalesced and the current free range is
8458 // in the free lists, remove the current free range so that it
8459 // will be returned to the free lists in its entirety - all
8460 // the coalesced pieces included.
8461 if (freeRangeInFreeLists()) {
8462 FreeChunk* ffc = (FreeChunk*) freeFinger();
8463 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8464 "Size of free range is inconsistent with chunk size.");
8465 if (CMSTestInFreeList) {
8466 assert(_sp->verify_chunk_in_free_list(ffc),
8467 "free range is not in free lists");
8468 }
8469 _sp->removeFreeChunkFromFreeLists(ffc);
8470 set_freeRangeInFreeLists(false);
8471 }
8472 }
8473 }
8474 // Note that if the chunk is not coalescable (the else arm
8475 // below), we unconditionally flush, without needing to do
8476 // a "lookahead," as we do below.
8477 if (inFreeRange()) lookahead_and_flush(fc, size);
8478 } else {
8479 // Code path common to both original and adaptive free lists.
8480
8481 // cant coalesce with previous block; this should be treated
8482 // as the end of a free run if any
8483 if (inFreeRange()) {
8484 // we kicked some butt; time to pick up the garbage
8485 assert(freeFinger() < addr, "freeFinger points too high");
8486 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8487 }
8488 // else, nothing to do, just continue
8489 }
8490 }
8491
8492 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8493 // This is a chunk of garbage. It is not in any free list.
8494 // Add it to a free list or let it possibly be coalesced into
8495 // a larger chunk.
8496 HeapWord* const addr = (HeapWord*) fc;
8497 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8498
8499 if (_sp->adaptive_freelists()) {
8500 // Verify that the bit map has no bits marked between
8501 // addr and purported end of just dead object.
8502 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8503
8504 do_post_free_or_garbage_chunk(fc, size);
8505 } else {
8506 if (!inFreeRange()) {
8507 // start of a new free range
8508 assert(size > 0, "A free range should have a size");
8509 initialize_free_range(addr, false);
8510 } else {
8511 // this will be swept up when we hit the end of the
8512 // free range
8513 if (CMSTraceSweeper) {
8514 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", fc, size);
8515 }
8516 // If the chunk is being coalesced and the current free range is
8517 // in the free lists, remove the current free range so that it
8518 // will be returned to the free lists in its entirety - all
8519 // the coalesced pieces included.
8520 if (freeRangeInFreeLists()) {
8521 FreeChunk* ffc = (FreeChunk*)freeFinger();
8522 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8523 "Size of free range is inconsistent with chunk size.");
8524 if (CMSTestInFreeList) {
8525 assert(_sp->verify_chunk_in_free_list(ffc),
8526 "free range is not in free lists");
8527 }
8528 _sp->removeFreeChunkFromFreeLists(ffc);
8529 set_freeRangeInFreeLists(false);
8530 }
8531 set_lastFreeRangeCoalesced(true);
8532 }
8533 // this will be swept up when we hit the end of the free range
8534
8535 // Verify that the bit map has no bits marked between
8536 // addr and purported end of just dead object.
8537 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8538 }
8539 assert(_limit >= addr + size,
8540 "A freshly garbage chunk can't possibly straddle over _limit");
8541 if (inFreeRange()) lookahead_and_flush(fc, size);
8542 return size;
8543 }
8544
8545 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8546 HeapWord* addr = (HeapWord*) fc;
8547 // The sweeper has just found a live object. Return any accumulated
8548 // left hand chunk to the free lists.
8549 if (inFreeRange()) {
8550 assert(freeFinger() < addr, "freeFinger points too high");
8551 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8552 }
8553
8554 // This object is live: we'd normally expect this to be
8555 // an oop, and like to assert the following:
8556 // assert(oop(addr)->is_oop(), "live block should be an oop");
8557 // However, as we commented above, this may be an object whose
8558 // header hasn't yet been initialized.
8559 size_t size;
8560 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8561 if (_bitMap->isMarked(addr + 1)) {
8562 // Determine the size from the bit map, rather than trying to
8563 // compute it from the object header.
8564 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8565 size = pointer_delta(nextOneAddr + 1, addr);
8566 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8567 "alignment problem");
8568
8569 #ifdef ASSERT
8570 if (oop(addr)->klass_or_null() != NULL) {
8571 // Ignore mark word because we are running concurrent with mutators
8572 assert(oop(addr)->is_oop(true), "live block should be an oop");
8573 assert(size ==
8574 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8575 "P-mark and computed size do not agree");
8576 }
8577 #endif
8578
8579 } else {
8580 // This should be an initialized object that's alive.
8581 assert(oop(addr)->klass_or_null() != NULL,
8582 "Should be an initialized object");
8583 // Ignore mark word because we are running concurrent with mutators
8584 assert(oop(addr)->is_oop(true), "live block should be an oop");
8585 // Verify that the bit map has no bits marked between
8586 // addr and purported end of this block.
8587 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8588 assert(size >= 3, "Necessary for Printezis marks to work");
8589 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8590 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8591 }
8592 return size;
8593 }
8594
8595 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8596 size_t chunkSize) {
8597 // do_post_free_or_garbage_chunk() should only be called in the case
8598 // of the adaptive free list allocator.
8599 const bool fcInFreeLists = fc->is_free();
8600 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8601 assert((HeapWord*)fc <= _limit, "sweep invariant");
8602 if (CMSTestInFreeList && fcInFreeLists) {
8603 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8604 }
8605
8606 if (CMSTraceSweeper) {
8607 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", fc, chunkSize);
8608 }
8609
8610 HeapWord* const fc_addr = (HeapWord*) fc;
8611
8612 bool coalesce;
8613 const size_t left = pointer_delta(fc_addr, freeFinger());
8614 const size_t right = chunkSize;
8615 switch (FLSCoalescePolicy) {
8616 // numeric value forms a coalition aggressiveness metric
8617 case 0: { // never coalesce
8618 coalesce = false;
8619 break;
8620 }
8621 case 1: { // coalesce if left & right chunks on overpopulated lists
8622 coalesce = _sp->coalOverPopulated(left) &&
8623 _sp->coalOverPopulated(right);
8624 break;
8625 }
8626 case 2: { // coalesce if left chunk on overpopulated list (default)
8627 coalesce = _sp->coalOverPopulated(left);
8628 break;
8629 }
8630 case 3: { // coalesce if left OR right chunk on overpopulated list
8631 coalesce = _sp->coalOverPopulated(left) ||
8632 _sp->coalOverPopulated(right);
8633 break;
8634 }
8635 case 4: { // always coalesce
8636 coalesce = true;
8637 break;
8638 }
8639 default:
8640 ShouldNotReachHere();
8641 }
8642
8643 // Should the current free range be coalesced?
8644 // If the chunk is in a free range and either we decided to coalesce above
8645 // or the chunk is near the large block at the end of the heap
8646 // (isNearLargestChunk() returns true), then coalesce this chunk.
8647 const bool doCoalesce = inFreeRange()
8648 && (coalesce || _g->isNearLargestChunk(fc_addr));
8649 if (doCoalesce) {
8650 // Coalesce the current free range on the left with the new
8651 // chunk on the right. If either is on a free list,
8652 // it must be removed from the list and stashed in the closure.
8653 if (freeRangeInFreeLists()) {
8654 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8655 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8656 "Size of free range is inconsistent with chunk size.");
8657 if (CMSTestInFreeList) {
8658 assert(_sp->verify_chunk_in_free_list(ffc),
8659 "Chunk is not in free lists");
8660 }
8661 _sp->coalDeath(ffc->size());
8662 _sp->removeFreeChunkFromFreeLists(ffc);
8663 set_freeRangeInFreeLists(false);
8664 }
8665 if (fcInFreeLists) {
8666 _sp->coalDeath(chunkSize);
8667 assert(fc->size() == chunkSize,
8668 "The chunk has the wrong size or is not in the free lists");
8669 _sp->removeFreeChunkFromFreeLists(fc);
8670 }
8671 set_lastFreeRangeCoalesced(true);
8672 print_free_block_coalesced(fc);
8673 } else { // not in a free range and/or should not coalesce
8674 // Return the current free range and start a new one.
8675 if (inFreeRange()) {
8676 // In a free range but cannot coalesce with the right hand chunk.
8677 // Put the current free range into the free lists.
8678 flush_cur_free_chunk(freeFinger(),
8679 pointer_delta(fc_addr, freeFinger()));
8680 }
8681 // Set up for new free range. Pass along whether the right hand
8682 // chunk is in the free lists.
8683 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8684 }
8685 }
8686
8687 // Lookahead flush:
8688 // If we are tracking a free range, and this is the last chunk that
8689 // we'll look at because its end crosses past _limit, we'll preemptively
8690 // flush it along with any free range we may be holding on to. Note that
8691 // this can be the case only for an already free or freshly garbage
8692 // chunk. If this block is an object, it can never straddle
8693 // over _limit. The "straddling" occurs when _limit is set at
8694 // the previous end of the space when this cycle started, and
8695 // a subsequent heap expansion caused the previously co-terminal
8696 // free block to be coalesced with the newly expanded portion,
8697 // thus rendering _limit a non-block-boundary making it dangerous
8698 // for the sweeper to step over and examine.
8699 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8700 assert(inFreeRange(), "Should only be called if currently in a free range.");
8701 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8702 assert(_sp->used_region().contains(eob - 1),
8703 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8704 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8705 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8706 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8707 if (eob >= _limit) {
8708 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8709 if (CMSTraceSweeper) {
8710 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8711 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8712 "[" PTR_FORMAT "," PTR_FORMAT ")",
8713 _limit, fc, eob, _sp->bottom(), _sp->end());
8714 }
8715 // Return the storage we are tracking back into the free lists.
8716 if (CMSTraceSweeper) {
8717 gclog_or_tty->print_cr("Flushing ... ");
8718 }
8719 assert(freeFinger() < eob, "Error");
8720 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8721 }
8722 }
8723
8724 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8725 assert(inFreeRange(), "Should only be called if currently in a free range.");
8726 assert(size > 0,
8727 "A zero sized chunk cannot be added to the free lists.");
8728 if (!freeRangeInFreeLists()) {
8729 if (CMSTestInFreeList) {
8730 FreeChunk* fc = (FreeChunk*) chunk;
8731 fc->set_size(size);
8732 assert(!_sp->verify_chunk_in_free_list(fc),
8733 "chunk should not be in free lists yet");
8734 }
8735 if (CMSTraceSweeper) {
8736 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
8737 chunk, size);
8738 }
8739 // A new free range is going to be starting. The current
8740 // free range has not been added to the free lists yet or
8741 // was removed so add it back.
8742 // If the current free range was coalesced, then the death
8743 // of the free range was recorded. Record a birth now.
8744 if (lastFreeRangeCoalesced()) {
8745 _sp->coalBirth(size);
8746 }
8747 _sp->addChunkAndRepairOffsetTable(chunk, size,
8748 lastFreeRangeCoalesced());
8749 } else if (CMSTraceSweeper) {
8750 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8751 }
8752 set_inFreeRange(false);
8753 set_freeRangeInFreeLists(false);
8754 }
8755
8756 // We take a break if we've been at this for a while,
8757 // so as to avoid monopolizing the locks involved.
8758 void SweepClosure::do_yield_work(HeapWord* addr) {
8759 // Return current free chunk being used for coalescing (if any)
8760 // to the appropriate freelist. After yielding, the next
8761 // free block encountered will start a coalescing range of
8762 // free blocks. If the next free block is adjacent to the
8763 // chunk just flushed, they will need to wait for the next
8764 // sweep to be coalesced.
8765 if (inFreeRange()) {
8766 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8767 }
8768
8769 // First give up the locks, then yield, then re-lock.
8770 // We should probably use a constructor/destructor idiom to
8771 // do this unlock/lock or modify the MutexUnlocker class to
8772 // serve our purpose. XXX
8773 assert_lock_strong(_bitMap->lock());
8774 assert_lock_strong(_freelistLock);
8775 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8776 "CMS thread should hold CMS token");
8777 _bitMap->lock()->unlock();
8778 _freelistLock->unlock();
8779 ConcurrentMarkSweepThread::desynchronize(true);
8780 ConcurrentMarkSweepThread::acknowledge_yield_request();
8781 _collector->stopTimer();
8782 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8783 if (PrintCMSStatistics != 0) {
8784 _collector->incrementYields();
8785 }
8786 _collector->icms_wait();
8787
8788 // See the comment in coordinator_yield()
8789 for (unsigned i = 0; i < CMSYieldSleepCount &&
8790 ConcurrentMarkSweepThread::should_yield() &&
8791 !CMSCollector::foregroundGCIsActive(); ++i) {
8792 os::sleep(Thread::current(), 1, false);
8793 ConcurrentMarkSweepThread::acknowledge_yield_request();
8794 }
8795
8796 ConcurrentMarkSweepThread::synchronize(true);
8797 _freelistLock->lock();
8798 _bitMap->lock()->lock_without_safepoint_check();
8799 _collector->startTimer();
8800 }
8801
8802 #ifndef PRODUCT
8803 // This is actually very useful in a product build if it can
8804 // be called from the debugger. Compile it into the product
8805 // as needed.
8806 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8807 return debug_cms_space->verify_chunk_in_free_list(fc);
8808 }
8809 #endif
8810
8811 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8812 if (CMSTraceSweeper) {
8813 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8814 fc, fc->size());
8815 }
8816 }
8817
8818 // CMSIsAliveClosure
8819 bool CMSIsAliveClosure::do_object_b(oop obj) {
8820 HeapWord* addr = (HeapWord*)obj;
8821 return addr != NULL &&
8822 (!_span.contains(addr) || _bit_map->isMarked(addr));
8823 }
8824
8825
8826 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8827 MemRegion span,
8828 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8829 bool cpc):
8830 _collector(collector),
8831 _span(span),
8832 _bit_map(bit_map),
8833 _mark_stack(mark_stack),
8834 _concurrent_precleaning(cpc) {
8835 assert(!_span.is_empty(), "Empty span could spell trouble");
8836 }
8837
8838
8839 // CMSKeepAliveClosure: the serial version
8840 void CMSKeepAliveClosure::do_oop(oop obj) {
8841 HeapWord* addr = (HeapWord*)obj;
8842 if (_span.contains(addr) &&
8843 !_bit_map->isMarked(addr)) {
8844 _bit_map->mark(addr);
8845 bool simulate_overflow = false;
8846 NOT_PRODUCT(
8847 if (CMSMarkStackOverflowALot &&
8848 _collector->simulate_overflow()) {
8849 // simulate a stack overflow
8850 simulate_overflow = true;
8851 }
8852 )
8853 if (simulate_overflow || !_mark_stack->push(obj)) {
8854 if (_concurrent_precleaning) {
8855 // We dirty the overflown object and let the remark
8856 // phase deal with it.
8857 assert(_collector->overflow_list_is_empty(), "Error");
8858 // In the case of object arrays, we need to dirty all of
8859 // the cards that the object spans. No locking or atomics
8860 // are needed since no one else can be mutating the mod union
8861 // table.
8862 if (obj->is_objArray()) {
8863 size_t sz = obj->size();
8864 HeapWord* end_card_addr =
8865 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8866 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8867 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8868 _collector->_modUnionTable.mark_range(redirty_range);
8869 } else {
8870 _collector->_modUnionTable.mark(addr);
8871 }
8872 _collector->_ser_kac_preclean_ovflw++;
8873 } else {
8874 _collector->push_on_overflow_list(obj);
8875 _collector->_ser_kac_ovflw++;
8876 }
8877 }
8878 }
8879 }
8880
8881 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8882 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8883
8884 // CMSParKeepAliveClosure: a parallel version of the above.
8885 // The work queues are private to each closure (thread),
8886 // but (may be) available for stealing by other threads.
8887 void CMSParKeepAliveClosure::do_oop(oop obj) {
8888 HeapWord* addr = (HeapWord*)obj;
8889 if (_span.contains(addr) &&
8890 !_bit_map->isMarked(addr)) {
8891 // In general, during recursive tracing, several threads
8892 // may be concurrently getting here; the first one to
8893 // "tag" it, claims it.
8894 if (_bit_map->par_mark(addr)) {
8895 bool res = _work_queue->push(obj);
8896 assert(res, "Low water mark should be much less than capacity");
8897 // Do a recursive trim in the hope that this will keep
8898 // stack usage lower, but leave some oops for potential stealers
8899 trim_queue(_low_water_mark);
8900 } // Else, another thread got there first
8901 }
8902 }
8903
8904 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8905 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8906
8907 void CMSParKeepAliveClosure::trim_queue(uint max) {
8908 while (_work_queue->size() > max) {
8909 oop new_oop;
8910 if (_work_queue->pop_local(new_oop)) {
8911 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8912 assert(_bit_map->isMarked((HeapWord*)new_oop),
8913 "no white objects on this stack!");
8914 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8915 // iterate over the oops in this oop, marking and pushing
8916 // the ones in CMS heap (i.e. in _span).
8917 new_oop->oop_iterate(&_mark_and_push);
8918 }
8919 }
8920 }
8921
8922 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8923 CMSCollector* collector,
8924 MemRegion span, CMSBitMap* bit_map,
8925 OopTaskQueue* work_queue):
8926 _collector(collector),
8927 _span(span),
8928 _bit_map(bit_map),
8929 _work_queue(work_queue) { }
8930
8931 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8932 HeapWord* addr = (HeapWord*)obj;
8933 if (_span.contains(addr) &&
8934 !_bit_map->isMarked(addr)) {
8935 if (_bit_map->par_mark(addr)) {
8936 bool simulate_overflow = false;
8937 NOT_PRODUCT(
8938 if (CMSMarkStackOverflowALot &&
8939 _collector->par_simulate_overflow()) {
8940 // simulate a stack overflow
8941 simulate_overflow = true;
8942 }
8943 )
8944 if (simulate_overflow || !_work_queue->push(obj)) {
8945 _collector->par_push_on_overflow_list(obj);
8946 _collector->_par_kac_ovflw++;
8947 }
8948 } // Else another thread got there already
8949 }
8950 }
8951
8952 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8953 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8954
8955 //////////////////////////////////////////////////////////////////
8956 // CMSExpansionCause /////////////////////////////
8957 //////////////////////////////////////////////////////////////////
8958 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8959 switch (cause) {
8960 case _no_expansion:
8961 return "No expansion";
8962 case _satisfy_free_ratio:
8963 return "Free ratio";
8964 case _satisfy_promotion:
8965 return "Satisfy promotion";
8966 case _satisfy_allocation:
8967 return "allocation";
8968 case _allocate_par_lab:
8969 return "Par LAB";
8970 case _allocate_par_spooling_space:
8971 return "Par Spooling Space";
8972 case _adaptive_size_policy:
8973 return "Ergonomics";
8974 default:
8975 return "unknown";
8976 }
8977 }
8978
8979 void CMSDrainMarkingStackClosure::do_void() {
8980 // the max number to take from overflow list at a time
8981 const size_t num = _mark_stack->capacity()/4;
8982 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8983 "Overflow list should be NULL during concurrent phases");
8984 while (!_mark_stack->isEmpty() ||
8985 // if stack is empty, check the overflow list
8986 _collector->take_from_overflow_list(num, _mark_stack)) {
8987 oop obj = _mark_stack->pop();
8988 HeapWord* addr = (HeapWord*)obj;
8989 assert(_span.contains(addr), "Should be within span");
8990 assert(_bit_map->isMarked(addr), "Should be marked");
8991 assert(obj->is_oop(), "Should be an oop");
8992 obj->oop_iterate(_keep_alive);
8993 }
8994 }
8995
8996 void CMSParDrainMarkingStackClosure::do_void() {
8997 // drain queue
8998 trim_queue(0);
8999 }
9000
9001 // Trim our work_queue so its length is below max at return
9002 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
9003 while (_work_queue->size() > max) {
9004 oop new_oop;
9005 if (_work_queue->pop_local(new_oop)) {
9006 assert(new_oop->is_oop(), "Expected an oop");
9007 assert(_bit_map->isMarked((HeapWord*)new_oop),
9008 "no white objects on this stack!");
9009 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
9010 // iterate over the oops in this oop, marking and pushing
9011 // the ones in CMS heap (i.e. in _span).
9012 new_oop->oop_iterate(&_mark_and_push);
9013 }
9014 }
9015 }
9016
9017 ////////////////////////////////////////////////////////////////////
9018 // Support for Marking Stack Overflow list handling and related code
9019 ////////////////////////////////////////////////////////////////////
9020 // Much of the following code is similar in shape and spirit to the
9021 // code used in ParNewGC. We should try and share that code
9022 // as much as possible in the future.
9023
9024 #ifndef PRODUCT
9025 // Debugging support for CMSStackOverflowALot
9026
9027 // It's OK to call this multi-threaded; the worst thing
9028 // that can happen is that we'll get a bunch of closely
9029 // spaced simulated overflows, but that's OK, in fact
9030 // probably good as it would exercise the overflow code
9031 // under contention.
9032 bool CMSCollector::simulate_overflow() {
9033 if (_overflow_counter-- <= 0) { // just being defensive
9034 _overflow_counter = CMSMarkStackOverflowInterval;
9035 return true;
9036 } else {
9037 return false;
9038 }
9039 }
9040
9041 bool CMSCollector::par_simulate_overflow() {
9042 return simulate_overflow();
9043 }
9044 #endif
9045
9046 // Single-threaded
9047 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9048 assert(stack->isEmpty(), "Expected precondition");
9049 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9050 size_t i = num;
9051 oop cur = _overflow_list;
9052 const markOop proto = markOopDesc::prototype();
9053 NOT_PRODUCT(ssize_t n = 0;)
9054 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9055 next = oop(cur->mark());
9056 cur->set_mark(proto); // until proven otherwise
9057 assert(cur->is_oop(), "Should be an oop");
9058 bool res = stack->push(cur);
9059 assert(res, "Bit off more than can chew?");
9060 NOT_PRODUCT(n++;)
9061 }
9062 _overflow_list = cur;
9063 #ifndef PRODUCT
9064 assert(_num_par_pushes >= n, "Too many pops?");
9065 _num_par_pushes -=n;
9066 #endif
9067 return !stack->isEmpty();
9068 }
9069
9070 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9071 // (MT-safe) Get a prefix of at most "num" from the list.
9072 // The overflow list is chained through the mark word of
9073 // each object in the list. We fetch the entire list,
9074 // break off a prefix of the right size and return the
9075 // remainder. If other threads try to take objects from
9076 // the overflow list at that time, they will wait for
9077 // some time to see if data becomes available. If (and
9078 // only if) another thread places one or more object(s)
9079 // on the global list before we have returned the suffix
9080 // to the global list, we will walk down our local list
9081 // to find its end and append the global list to
9082 // our suffix before returning it. This suffix walk can
9083 // prove to be expensive (quadratic in the amount of traffic)
9084 // when there are many objects in the overflow list and
9085 // there is much producer-consumer contention on the list.
9086 // *NOTE*: The overflow list manipulation code here and
9087 // in ParNewGeneration:: are very similar in shape,
9088 // except that in the ParNew case we use the old (from/eden)
9089 // copy of the object to thread the list via its klass word.
9090 // Because of the common code, if you make any changes in
9091 // the code below, please check the ParNew version to see if
9092 // similar changes might be needed.
9093 // CR 6797058 has been filed to consolidate the common code.
9094 bool CMSCollector::par_take_from_overflow_list(size_t num,
9095 OopTaskQueue* work_q,
9096 int no_of_gc_threads) {
9097 assert(work_q->size() == 0, "First empty local work queue");
9098 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9099 if (_overflow_list == NULL) {
9100 return false;
9101 }
9102 // Grab the entire list; we'll put back a suffix
9103 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9104 Thread* tid = Thread::current();
9105 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9106 // set to ParallelGCThreads.
9107 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9108 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9109 // If the list is busy, we spin for a short while,
9110 // sleeping between attempts to get the list.
9111 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9112 os::sleep(tid, sleep_time_millis, false);
9113 if (_overflow_list == NULL) {
9114 // Nothing left to take
9115 return false;
9116 } else if (_overflow_list != BUSY) {
9117 // Try and grab the prefix
9118 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9119 }
9120 }
9121 // If the list was found to be empty, or we spun long
9122 // enough, we give up and return empty-handed. If we leave
9123 // the list in the BUSY state below, it must be the case that
9124 // some other thread holds the overflow list and will set it
9125 // to a non-BUSY state in the future.
9126 if (prefix == NULL || prefix == BUSY) {
9127 // Nothing to take or waited long enough
9128 if (prefix == NULL) {
9129 // Write back the NULL in case we overwrote it with BUSY above
9130 // and it is still the same value.
9131 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9132 }
9133 return false;
9134 }
9135 assert(prefix != NULL && prefix != BUSY, "Error");
9136 size_t i = num;
9137 oop cur = prefix;
9138 // Walk down the first "num" objects, unless we reach the end.
9139 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9140 if (cur->mark() == NULL) {
9141 // We have "num" or fewer elements in the list, so there
9142 // is nothing to return to the global list.
9143 // Write back the NULL in lieu of the BUSY we wrote
9144 // above, if it is still the same value.
9145 if (_overflow_list == BUSY) {
9146 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9147 }
9148 } else {
9149 // Chop off the suffix and return it to the global list.
9150 assert(cur->mark() != BUSY, "Error");
9151 oop suffix_head = cur->mark(); // suffix will be put back on global list
9152 cur->set_mark(NULL); // break off suffix
9153 // It's possible that the list is still in the empty(busy) state
9154 // we left it in a short while ago; in that case we may be
9155 // able to place back the suffix without incurring the cost
9156 // of a walk down the list.
9157 oop observed_overflow_list = _overflow_list;
9158 oop cur_overflow_list = observed_overflow_list;
9159 bool attached = false;
9160 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9161 observed_overflow_list =
9162 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9163 if (cur_overflow_list == observed_overflow_list) {
9164 attached = true;
9165 break;
9166 } else cur_overflow_list = observed_overflow_list;
9167 }
9168 if (!attached) {
9169 // Too bad, someone else sneaked in (at least) an element; we'll need
9170 // to do a splice. Find tail of suffix so we can prepend suffix to global
9171 // list.
9172 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9173 oop suffix_tail = cur;
9174 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9175 "Tautology");
9176 observed_overflow_list = _overflow_list;
9177 do {
9178 cur_overflow_list = observed_overflow_list;
9179 if (cur_overflow_list != BUSY) {
9180 // Do the splice ...
9181 suffix_tail->set_mark(markOop(cur_overflow_list));
9182 } else { // cur_overflow_list == BUSY
9183 suffix_tail->set_mark(NULL);
9184 }
9185 // ... and try to place spliced list back on overflow_list ...
9186 observed_overflow_list =
9187 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9188 } while (cur_overflow_list != observed_overflow_list);
9189 // ... until we have succeeded in doing so.
9190 }
9191 }
9192
9193 // Push the prefix elements on work_q
9194 assert(prefix != NULL, "control point invariant");
9195 const markOop proto = markOopDesc::prototype();
9196 oop next;
9197 NOT_PRODUCT(ssize_t n = 0;)
9198 for (cur = prefix; cur != NULL; cur = next) {
9199 next = oop(cur->mark());
9200 cur->set_mark(proto); // until proven otherwise
9201 assert(cur->is_oop(), "Should be an oop");
9202 bool res = work_q->push(cur);
9203 assert(res, "Bit off more than we can chew?");
9204 NOT_PRODUCT(n++;)
9205 }
9206 #ifndef PRODUCT
9207 assert(_num_par_pushes >= n, "Too many pops?");
9208 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9209 #endif
9210 return true;
9211 }
9212
9213 // Single-threaded
9214 void CMSCollector::push_on_overflow_list(oop p) {
9215 NOT_PRODUCT(_num_par_pushes++;)
9216 assert(p->is_oop(), "Not an oop");
9217 preserve_mark_if_necessary(p);
9218 p->set_mark((markOop)_overflow_list);
9219 _overflow_list = p;
9220 }
9221
9222 // Multi-threaded; use CAS to prepend to overflow list
9223 void CMSCollector::par_push_on_overflow_list(oop p) {
9224 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9225 assert(p->is_oop(), "Not an oop");
9226 par_preserve_mark_if_necessary(p);
9227 oop observed_overflow_list = _overflow_list;
9228 oop cur_overflow_list;
9229 do {
9230 cur_overflow_list = observed_overflow_list;
9231 if (cur_overflow_list != BUSY) {
9232 p->set_mark(markOop(cur_overflow_list));
9233 } else {
9234 p->set_mark(NULL);
9235 }
9236 observed_overflow_list =
9237 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9238 } while (cur_overflow_list != observed_overflow_list);
9239 }
9240 #undef BUSY
9241
9242 // Single threaded
9243 // General Note on GrowableArray: pushes may silently fail
9244 // because we are (temporarily) out of C-heap for expanding
9245 // the stack. The problem is quite ubiquitous and affects
9246 // a lot of code in the JVM. The prudent thing for GrowableArray
9247 // to do (for now) is to exit with an error. However, that may
9248 // be too draconian in some cases because the caller may be
9249 // able to recover without much harm. For such cases, we
9250 // should probably introduce a "soft_push" method which returns
9251 // an indication of success or failure with the assumption that
9252 // the caller may be able to recover from a failure; code in
9253 // the VM can then be changed, incrementally, to deal with such
9254 // failures where possible, thus, incrementally hardening the VM
9255 // in such low resource situations.
9256 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9257 _preserved_oop_stack.push(p);
9258 _preserved_mark_stack.push(m);
9259 assert(m == p->mark(), "Mark word changed");
9260 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9261 "bijection");
9262 }
9263
9264 // Single threaded
9265 void CMSCollector::preserve_mark_if_necessary(oop p) {
9266 markOop m = p->mark();
9267 if (m->must_be_preserved(p)) {
9268 preserve_mark_work(p, m);
9269 }
9270 }
9271
9272 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9273 markOop m = p->mark();
9274 if (m->must_be_preserved(p)) {
9275 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9276 // Even though we read the mark word without holding
9277 // the lock, we are assured that it will not change
9278 // because we "own" this oop, so no other thread can
9279 // be trying to push it on the overflow list; see
9280 // the assertion in preserve_mark_work() that checks
9281 // that m == p->mark().
9282 preserve_mark_work(p, m);
9283 }
9284 }
9285
9286 // We should be able to do this multi-threaded,
9287 // a chunk of stack being a task (this is
9288 // correct because each oop only ever appears
9289 // once in the overflow list. However, it's
9290 // not very easy to completely overlap this with
9291 // other operations, so will generally not be done
9292 // until all work's been completed. Because we
9293 // expect the preserved oop stack (set) to be small,
9294 // it's probably fine to do this single-threaded.
9295 // We can explore cleverer concurrent/overlapped/parallel
9296 // processing of preserved marks if we feel the
9297 // need for this in the future. Stack overflow should
9298 // be so rare in practice and, when it happens, its
9299 // effect on performance so great that this will
9300 // likely just be in the noise anyway.
9301 void CMSCollector::restore_preserved_marks_if_any() {
9302 assert(SafepointSynchronize::is_at_safepoint(),
9303 "world should be stopped");
9304 assert(Thread::current()->is_ConcurrentGC_thread() ||
9305 Thread::current()->is_VM_thread(),
9306 "should be single-threaded");
9307 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9308 "bijection");
9309
9310 while (!_preserved_oop_stack.is_empty()) {
9311 oop p = _preserved_oop_stack.pop();
9312 assert(p->is_oop(), "Should be an oop");
9313 assert(_span.contains(p), "oop should be in _span");
9314 assert(p->mark() == markOopDesc::prototype(),
9315 "Set when taken from overflow list");
9316 markOop m = _preserved_mark_stack.pop();
9317 p->set_mark(m);
9318 }
9319 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9320 "stacks were cleared above");
9321 }
9322
9323 #ifndef PRODUCT
9324 bool CMSCollector::no_preserved_marks() const {
9325 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9326 }
9327 #endif
9328
9329 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9330 {
9331 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9332 CMSAdaptiveSizePolicy* size_policy =
9333 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9334 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9335 "Wrong type for size policy");
9336 return size_policy;
9337 }
9338
9339 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9340 size_t desired_promo_size) {
9341 if (cur_promo_size < desired_promo_size) {
9342 size_t expand_bytes = desired_promo_size - cur_promo_size;
9343 if (PrintAdaptiveSizePolicy && Verbose) {
9344 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9345 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9346 expand_bytes);
9347 }
9348 expand(expand_bytes,
9349 MinHeapDeltaBytes,
9350 CMSExpansionCause::_adaptive_size_policy);
9351 } else if (desired_promo_size < cur_promo_size) {
9352 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9353 if (PrintAdaptiveSizePolicy && Verbose) {
9354 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9355 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9356 shrink_bytes);
9357 }
9358 shrink(shrink_bytes);
9359 }
9360 }
9361
9362 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9363 GenCollectedHeap* gch = GenCollectedHeap::heap();
9364 CMSGCAdaptivePolicyCounters* counters =
9365 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9366 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9367 "Wrong kind of counters");
9368 return counters;
9369 }
9370
9371
9372 void ASConcurrentMarkSweepGeneration::update_counters() {
9373 if (UsePerfData) {
9374 _space_counters->update_all();
9375 _gen_counters->update_all();
9376 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9377 GenCollectedHeap* gch = GenCollectedHeap::heap();
9378 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9379 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9380 "Wrong gc statistics type");
9381 counters->update_counters(gc_stats_l);
9382 }
9383 }
9384
9385 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9386 if (UsePerfData) {
9387 _space_counters->update_used(used);
9388 _space_counters->update_capacity();
9389 _gen_counters->update_all();
9390
9391 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9392 GenCollectedHeap* gch = GenCollectedHeap::heap();
9393 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9394 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9395 "Wrong gc statistics type");
9396 counters->update_counters(gc_stats_l);
9397 }
9398 }
9399
9400 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9401 assert_locked_or_safepoint(Heap_lock);
9402 assert_lock_strong(freelistLock());
9403 HeapWord* old_end = _cmsSpace->end();
9404 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9405 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9406 FreeChunk* chunk_at_end = find_chunk_at_end();
9407 if (chunk_at_end == NULL) {
9408 // No room to shrink
9409 if (PrintGCDetails && Verbose) {
9410 gclog_or_tty->print_cr("No room to shrink: old_end "
9411 PTR_FORMAT " unallocated_start " PTR_FORMAT
9412 " chunk_at_end " PTR_FORMAT,
9413 old_end, unallocated_start, chunk_at_end);
9414 }
9415 return;
9416 } else {
9417
9418 // Find the chunk at the end of the space and determine
9419 // how much it can be shrunk.
9420 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9421 size_t aligned_shrinkable_size_in_bytes =
9422 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9423 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9424 "Inconsistent chunk at end of space");
9425 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9426 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9427
9428 // Shrink the underlying space
9429 _virtual_space.shrink_by(bytes);
9430 if (PrintGCDetails && Verbose) {
9431 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9432 " desired_bytes " SIZE_FORMAT
9433 " shrinkable_size_in_bytes " SIZE_FORMAT
9434 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9435 " bytes " SIZE_FORMAT,
9436 desired_bytes, shrinkable_size_in_bytes,
9437 aligned_shrinkable_size_in_bytes, bytes);
9438 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9439 " unallocated_start " SIZE_FORMAT,
9440 old_end, unallocated_start);
9441 }
9442
9443 // If the space did shrink (shrinking is not guaranteed),
9444 // shrink the chunk at the end by the appropriate amount.
9445 if (((HeapWord*)_virtual_space.high()) < old_end) {
9446 size_t new_word_size =
9447 heap_word_size(_virtual_space.committed_size());
9448
9449 // Have to remove the chunk from the dictionary because it is changing
9450 // size and might be someplace elsewhere in the dictionary.
9451
9452 // Get the chunk at end, shrink it, and put it
9453 // back.
9454 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9455 size_t word_size_change = word_size_before - new_word_size;
9456 size_t chunk_at_end_old_size = chunk_at_end->size();
9457 assert(chunk_at_end_old_size >= word_size_change,
9458 "Shrink is too large");
9459 chunk_at_end->set_size(chunk_at_end_old_size -
9460 word_size_change);
9461 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9462 word_size_change);
9463
9464 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9465
9466 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9467 _bts->resize(new_word_size); // resize the block offset shared array
9468 Universe::heap()->barrier_set()->resize_covered_region(mr);
9469 _cmsSpace->assert_locked();
9470 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9471
9472 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9473
9474 // update the space and generation capacity counters
9475 if (UsePerfData) {
9476 _space_counters->update_capacity();
9477 _gen_counters->update_all();
9478 }
9479
9480 if (Verbose && PrintGCDetails) {
9481 size_t new_mem_size = _virtual_space.committed_size();
9482 size_t old_mem_size = new_mem_size + bytes;
9483 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9484 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9485 }
9486 }
9487
9488 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9489 "Inconsistency at end of space");
9490 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9491 "Shrinking is inconsistent");
9492 return;
9493 }
9494 }
9495 // Transfer some number of overflown objects to usual marking
9496 // stack. Return true if some objects were transferred.
9497 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9498 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9499 (size_t)ParGCDesiredObjsFromOverflowList);
9500
9501 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9502 assert(_collector->overflow_list_is_empty() || res,
9503 "If list is not empty, we should have taken something");
9504 assert(!res || !_mark_stack->isEmpty(),
9505 "If we took something, it should now be on our stack");
9506 return res;
9507 }
9508
9509 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9510 size_t res = _sp->block_size_no_stall(addr, _collector);
9511 if (_sp->block_is_obj(addr)) {
9512 if (_live_bit_map->isMarked(addr)) {
9513 // It can't have been dead in a previous cycle
9514 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9515 } else {
9516 _dead_bit_map->mark(addr); // mark the dead object
9517 }
9518 }
9519 // Could be 0, if the block size could not be computed without stalling.
9520 return res;
9521 }
9522
9523 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9524
9525 switch (phase) {
9526 case CMSCollector::InitialMarking:
9527 initialize(true /* fullGC */ ,
9528 cause /* cause of the GC */,
9529 true /* recordGCBeginTime */,
9530 true /* recordPreGCUsage */,
9531 false /* recordPeakUsage */,
9532 false /* recordPostGCusage */,
9533 true /* recordAccumulatedGCTime */,
9534 false /* recordGCEndTime */,
9535 false /* countCollection */ );
9536 break;
9537
9538 case CMSCollector::FinalMarking:
9539 initialize(true /* fullGC */ ,
9540 cause /* cause of the GC */,
9541 false /* recordGCBeginTime */,
9542 false /* recordPreGCUsage */,
9543 false /* recordPeakUsage */,
9544 false /* recordPostGCusage */,
9545 true /* recordAccumulatedGCTime */,
9546 false /* recordGCEndTime */,
9547 false /* countCollection */ );
9548 break;
9549
9550 case CMSCollector::Sweeping:
9551 initialize(true /* fullGC */ ,
9552 cause /* cause of the GC */,
9553 false /* recordGCBeginTime */,
9554 false /* recordPreGCUsage */,
9555 true /* recordPeakUsage */,
9556 true /* recordPostGCusage */,
9557 false /* recordAccumulatedGCTime */,
9558 true /* recordGCEndTime */,
9559 true /* countCollection */ );
9560 break;
9561
9562 default:
9563 ShouldNotReachHere();
9564 }
9565 }