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 "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
  27 #include "gc_implementation/parNew/parNewGeneration.hpp"
  28 #include "gc_implementation/parNew/parOopClosures.inline.hpp"
  29 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
  30 #include "gc_implementation/shared/ageTable.hpp"
  31 #include "gc_implementation/shared/parGCAllocBuffer.hpp"
  32 #include "gc_implementation/shared/gcHeapSummary.hpp"
  33 #include "gc_implementation/shared/gcTimer.hpp"
  34 #include "gc_implementation/shared/gcTrace.hpp"
  35 #include "gc_implementation/shared/gcTraceTime.hpp"
  36 #include "gc_implementation/shared/copyFailedInfo.hpp"
  37 #include "gc_implementation/shared/spaceDecorator.hpp"
  38 #include "memory/defNewGeneration.inline.hpp"
  39 #include "memory/genCollectedHeap.hpp"
  40 #include "memory/genOopClosures.inline.hpp"
  41 #include "memory/generation.hpp"
  42 #include "memory/generation.inline.hpp"
  43 #include "memory/referencePolicy.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/sharedHeap.hpp"
  46 #include "memory/space.hpp"
  47 #include "oops/objArrayOop.hpp"
  48 #include "oops/oop.inline.hpp"
  49 #include "oops/oop.pcgc.inline.hpp"
  50 #include "runtime/handles.hpp"
  51 #include "runtime/handles.inline.hpp"
  52 #include "runtime/java.hpp"
  53 #include "runtime/thread.inline.hpp"
  54 #include "utilities/copy.hpp"
  55 #include "utilities/globalDefinitions.hpp"
  56 #include "utilities/workgroup.hpp"
  57 
  58 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  59 
  60 #ifdef _MSC_VER
  61 #pragma warning( push )
  62 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
  63 #endif
  64 ParScanThreadState::ParScanThreadState(Space* to_space_,
  65                                        ParNewGeneration* gen_,
  66                                        Generation* old_gen_,
  67                                        int thread_num_,
  68                                        ObjToScanQueueSet* work_queue_set_,
  69                                        Stack<oop, mtGC>* overflow_stacks_,
  70                                        size_t desired_plab_sz_,
  71                                        ParallelTaskTerminator& term_) :
  72   _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
  73   _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
  74   _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
  75   _ageTable(false), // false ==> not the global age table, no perf data.
  76   _to_space_alloc_buffer(desired_plab_sz_),
  77   _to_space_closure(gen_, this), _old_gen_closure(gen_, this),
  78   _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this),
  79   _older_gen_closure(gen_, this),
  80   _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
  81                       &_to_space_root_closure, gen_, &_old_gen_root_closure,
  82                       work_queue_set_, &term_),
  83   _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this),
  84   _keep_alive_closure(&_scan_weak_ref_closure),
  85   _strong_roots_time(0.0), _term_time(0.0)
  86 {
  87   #if TASKQUEUE_STATS
  88   _term_attempts = 0;
  89   _overflow_refills = 0;
  90   _overflow_refill_objs = 0;
  91   #endif // TASKQUEUE_STATS
  92 
  93   _survivor_chunk_array =
  94     (ChunkArray*) old_gen()->get_data_recorder(thread_num());
  95   _hash_seed = 17;  // Might want to take time-based random value.
  96   _start = os::elapsedTime();
  97   _old_gen_closure.set_generation(old_gen_);
  98   _old_gen_root_closure.set_generation(old_gen_);
  99 }
 100 #ifdef _MSC_VER
 101 #pragma warning( pop )
 102 #endif
 103 
 104 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
 105                                               size_t plab_word_size) {
 106   ChunkArray* sca = survivor_chunk_array();
 107   if (sca != NULL) {
 108     // A non-null SCA implies that we want the PLAB data recorded.
 109     sca->record_sample(plab_start, plab_word_size);
 110   }
 111 }
 112 
 113 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
 114   return new_obj->is_objArray() &&
 115          arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
 116          new_obj != old_obj;
 117 }
 118 
 119 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
 120   assert(old->is_objArray(), "must be obj array");
 121   assert(old->is_forwarded(), "must be forwarded");
 122   assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
 123   assert(!old_gen()->is_in(old), "must be in young generation.");
 124 
 125   objArrayOop obj = objArrayOop(old->forwardee());
 126   // Process ParGCArrayScanChunk elements now
 127   // and push the remainder back onto queue
 128   int start     = arrayOop(old)->length();
 129   int end       = obj->length();
 130   int remainder = end - start;
 131   assert(start <= end, "just checking");
 132   if (remainder > 2 * ParGCArrayScanChunk) {
 133     // Test above combines last partial chunk with a full chunk
 134     end = start + ParGCArrayScanChunk;
 135     arrayOop(old)->set_length(end);
 136     // Push remainder.
 137     bool ok = work_queue()->push(old);
 138     assert(ok, "just popped, push must be okay");
 139   } else {
 140     // Restore length so that it can be used if there
 141     // is a promotion failure and forwarding pointers
 142     // must be removed.
 143     arrayOop(old)->set_length(end);
 144   }
 145 
 146   // process our set of indices (include header in first chunk)
 147   // should make sure end is even (aligned to HeapWord in case of compressed oops)
 148   if ((HeapWord *)obj < young_old_boundary()) {
 149     // object is in to_space
 150     obj->oop_iterate_range(&_to_space_closure, start, end);
 151   } else {
 152     // object is in old generation
 153     obj->oop_iterate_range(&_old_gen_closure, start, end);
 154   }
 155 }
 156 
 157 
 158 void ParScanThreadState::trim_queues(int max_size) {
 159   ObjToScanQueue* queue = work_queue();
 160   do {
 161     while (queue->size() > (juint)max_size) {
 162       oop obj_to_scan;
 163       if (queue->pop_local(obj_to_scan)) {
 164         if ((HeapWord *)obj_to_scan < young_old_boundary()) {
 165           if (obj_to_scan->is_objArray() &&
 166               obj_to_scan->is_forwarded() &&
 167               obj_to_scan->forwardee() != obj_to_scan) {
 168             scan_partial_array_and_push_remainder(obj_to_scan);
 169           } else {
 170             // object is in to_space
 171             obj_to_scan->oop_iterate(&_to_space_closure);
 172           }
 173         } else {
 174           // object is in old generation
 175           obj_to_scan->oop_iterate(&_old_gen_closure);
 176         }
 177       }
 178     }
 179     // For the  case of compressed oops, we have a private, non-shared
 180     // overflow stack, so we eagerly drain it so as to more evenly
 181     // distribute load early. Note: this may be good to do in
 182     // general rather than delay for the final stealing phase.
 183     // If applicable, we'll transfer a set of objects over to our
 184     // work queue, allowing them to be stolen and draining our
 185     // private overflow stack.
 186   } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
 187 }
 188 
 189 bool ParScanThreadState::take_from_overflow_stack() {
 190   assert(ParGCUseLocalOverflow, "Else should not call");
 191   assert(young_gen()->overflow_list() == NULL, "Error");
 192   ObjToScanQueue* queue = work_queue();
 193   Stack<oop, mtGC>* const of_stack = overflow_stack();
 194   const size_t num_overflow_elems = of_stack->size();
 195   const size_t space_available = queue->max_elems() - queue->size();
 196   const size_t num_take_elems = MIN3(space_available / 4,
 197                                      (size_t)ParGCDesiredObjsFromOverflowList,
 198                                      num_overflow_elems);
 199   // Transfer the most recent num_take_elems from the overflow
 200   // stack to our work queue.
 201   for (size_t i = 0; i != num_take_elems; i++) {
 202     oop cur = of_stack->pop();
 203     oop obj_to_push = cur->forwardee();
 204     assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
 205     assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
 206     assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
 207     if (should_be_partially_scanned(obj_to_push, cur)) {
 208       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
 209       obj_to_push = cur;
 210     }
 211     bool ok = queue->push(obj_to_push);
 212     assert(ok, "Should have succeeded");
 213   }
 214   assert(young_gen()->overflow_list() == NULL, "Error");
 215   return num_take_elems > 0;  // was something transferred?
 216 }
 217 
 218 void ParScanThreadState::push_on_overflow_stack(oop p) {
 219   assert(ParGCUseLocalOverflow, "Else should not call");
 220   overflow_stack()->push(p);
 221   assert(young_gen()->overflow_list() == NULL, "Error");
 222 }
 223 
 224 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
 225 
 226   // Otherwise, if the object is small enough, try to reallocate the
 227   // buffer.
 228   HeapWord* obj = NULL;
 229   if (!_to_space_full) {
 230     ParGCAllocBuffer* const plab = to_space_alloc_buffer();
 231     Space*            const sp   = to_space();
 232     if (word_sz * 100 <
 233         ParallelGCBufferWastePct * plab->word_sz()) {
 234       // Is small enough; abandon this buffer and start a new one.
 235       plab->retire(false, false);
 236       size_t buf_size = plab->word_sz();
 237       HeapWord* buf_space = sp->par_allocate(buf_size);
 238       if (buf_space == NULL) {
 239         const size_t min_bytes =
 240           ParGCAllocBuffer::min_size() << LogHeapWordSize;
 241         size_t free_bytes = sp->free();
 242         while(buf_space == NULL && free_bytes >= min_bytes) {
 243           buf_size = free_bytes >> LogHeapWordSize;
 244           assert(buf_size == (size_t)align_object_size(buf_size),
 245                  "Invariant");
 246           buf_space  = sp->par_allocate(buf_size);
 247           free_bytes = sp->free();
 248         }
 249       }
 250       if (buf_space != NULL) {
 251         plab->set_word_size(buf_size);
 252         plab->set_buf(buf_space);
 253         record_survivor_plab(buf_space, buf_size);
 254         obj = plab->allocate(word_sz);
 255         // Note that we cannot compare buf_size < word_sz below
 256         // because of AlignmentReserve (see ParGCAllocBuffer::allocate()).
 257         assert(obj != NULL || plab->words_remaining() < word_sz,
 258                "Else should have been able to allocate");
 259         // It's conceivable that we may be able to use the
 260         // buffer we just grabbed for subsequent small requests
 261         // even if not for this one.
 262       } else {
 263         // We're used up.
 264         _to_space_full = true;
 265       }
 266 
 267     } else {
 268       // Too large; allocate the object individually.
 269       obj = sp->par_allocate(word_sz);
 270     }
 271   }
 272   return obj;
 273 }
 274 
 275 
 276 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,
 277                                                 size_t word_sz) {
 278   // Is the alloc in the current alloc buffer?
 279   if (to_space_alloc_buffer()->contains(obj)) {
 280     assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),
 281            "Should contain whole object.");
 282     to_space_alloc_buffer()->undo_allocation(obj, word_sz);
 283   } else {
 284     CollectedHeap::fill_with_object(obj, word_sz);
 285   }
 286 }
 287 
 288 void ParScanThreadState::print_promotion_failure_size() {
 289   if (_promotion_failed_info.has_failed() && PrintPromotionFailure) {
 290     gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
 291                         _thread_num, _promotion_failed_info.first_size());
 292   }
 293 }
 294 
 295 class ParScanThreadStateSet: private ResourceArray {
 296 public:
 297   // Initializes states for the specified number of threads;
 298   ParScanThreadStateSet(int                     num_threads,
 299                         Space&                  to_space,
 300                         ParNewGeneration&       gen,
 301                         Generation&             old_gen,
 302                         ObjToScanQueueSet&      queue_set,
 303                         Stack<oop, mtGC>*       overflow_stacks_,
 304                         size_t                  desired_plab_sz,
 305                         ParallelTaskTerminator& term);
 306 
 307   ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
 308 
 309   inline ParScanThreadState& thread_state(int i);
 310 
 311   void trace_promotion_failed(YoungGCTracer& gc_tracer);
 312   void reset(int active_workers, bool promotion_failed);
 313   void flush();
 314 
 315   #if TASKQUEUE_STATS
 316   static void
 317     print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
 318   void print_termination_stats(outputStream* const st = gclog_or_tty);
 319   static void
 320     print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
 321   void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
 322   void reset_stats();
 323   #endif // TASKQUEUE_STATS
 324 
 325 private:
 326   ParallelTaskTerminator& _term;
 327   ParNewGeneration&       _gen;
 328   Generation&             _next_gen;
 329  public:
 330   bool is_valid(int id) const { return id < length(); }
 331   ParallelTaskTerminator* terminator() { return &_term; }
 332 };
 333 
 334 
 335 ParScanThreadStateSet::ParScanThreadStateSet(
 336   int num_threads, Space& to_space, ParNewGeneration& gen,
 337   Generation& old_gen, ObjToScanQueueSet& queue_set,
 338   Stack<oop, mtGC>* overflow_stacks,
 339   size_t desired_plab_sz, ParallelTaskTerminator& term)
 340   : ResourceArray(sizeof(ParScanThreadState), num_threads),
 341     _gen(gen), _next_gen(old_gen), _term(term)
 342 {
 343   assert(num_threads > 0, "sanity check!");
 344   assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
 345          "overflow_stack allocation mismatch");
 346   // Initialize states.
 347   for (int i = 0; i < num_threads; ++i) {
 348     new ((ParScanThreadState*)_data + i)
 349         ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
 350                            overflow_stacks, desired_plab_sz, term);
 351   }
 352 }
 353 
 354 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
 355 {
 356   assert(i >= 0 && i < length(), "sanity check!");
 357   return ((ParScanThreadState*)_data)[i];
 358 }
 359 
 360 void ParScanThreadStateSet::trace_promotion_failed(YoungGCTracer& gc_tracer) {
 361   for (int i = 0; i < length(); ++i) {
 362     if (thread_state(i).promotion_failed()) {
 363       gc_tracer.report_promotion_failed(thread_state(i).promotion_failed_info());
 364       thread_state(i).promotion_failed_info().reset();
 365     }
 366   }
 367 }
 368 
 369 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed)
 370 {
 371   _term.reset_for_reuse(active_threads);
 372   if (promotion_failed) {
 373     for (int i = 0; i < length(); ++i) {
 374       thread_state(i).print_promotion_failure_size();
 375     }
 376   }
 377 }
 378 
 379 #if TASKQUEUE_STATS
 380 void
 381 ParScanThreadState::reset_stats()
 382 {
 383   taskqueue_stats().reset();
 384   _term_attempts = 0;
 385   _overflow_refills = 0;
 386   _overflow_refill_objs = 0;
 387 }
 388 
 389 void ParScanThreadStateSet::reset_stats()
 390 {
 391   for (int i = 0; i < length(); ++i) {
 392     thread_state(i).reset_stats();
 393   }
 394 }
 395 
 396 void
 397 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
 398 {
 399   st->print_raw_cr("GC Termination Stats");
 400   st->print_raw_cr("     elapsed  --strong roots-- "
 401                    "-------termination-------");
 402   st->print_raw_cr("thr     ms        ms       %   "
 403                    "    ms       %   attempts");
 404   st->print_raw_cr("--- --------- --------- ------ "
 405                    "--------- ------ --------");
 406 }
 407 
 408 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
 409 {
 410   print_termination_stats_hdr(st);
 411 
 412   for (int i = 0; i < length(); ++i) {
 413     const ParScanThreadState & pss = thread_state(i);
 414     const double elapsed_ms = pss.elapsed_time() * 1000.0;
 415     const double s_roots_ms = pss.strong_roots_time() * 1000.0;
 416     const double term_ms = pss.term_time() * 1000.0;
 417     st->print_cr("%3d %9.2f %9.2f %6.2f "
 418                  "%9.2f %6.2f " SIZE_FORMAT_W(8),
 419                  i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
 420                  term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
 421   }
 422 }
 423 
 424 // Print stats related to work queue activity.
 425 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
 426 {
 427   st->print_raw_cr("GC Task Stats");
 428   st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
 429   st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
 430 }
 431 
 432 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
 433 {
 434   print_taskqueue_stats_hdr(st);
 435 
 436   TaskQueueStats totals;
 437   for (int i = 0; i < length(); ++i) {
 438     const ParScanThreadState & pss = thread_state(i);
 439     const TaskQueueStats & stats = pss.taskqueue_stats();
 440     st->print("%3d ", i); stats.print(st); st->cr();
 441     totals += stats;
 442 
 443     if (pss.overflow_refills() > 0) {
 444       st->print_cr("    " SIZE_FORMAT_W(10) " overflow refills    "
 445                    SIZE_FORMAT_W(10) " overflow objects",
 446                    pss.overflow_refills(), pss.overflow_refill_objs());
 447     }
 448   }
 449   st->print("tot "); totals.print(st); st->cr();
 450 
 451   DEBUG_ONLY(totals.verify());
 452 }
 453 #endif // TASKQUEUE_STATS
 454 
 455 void ParScanThreadStateSet::flush()
 456 {
 457   // Work in this loop should be kept as lightweight as
 458   // possible since this might otherwise become a bottleneck
 459   // to scaling. Should we add heavy-weight work into this
 460   // loop, consider parallelizing the loop into the worker threads.
 461   for (int i = 0; i < length(); ++i) {
 462     ParScanThreadState& par_scan_state = thread_state(i);
 463 
 464     // Flush stats related to To-space PLAB activity and
 465     // retire the last buffer.
 466     par_scan_state.to_space_alloc_buffer()->
 467       flush_stats_and_retire(_gen.plab_stats(),
 468                              true /* end_of_gc */,
 469                              false /* retain */);
 470 
 471     // Every thread has its own age table.  We need to merge
 472     // them all into one.
 473     ageTable *local_table = par_scan_state.age_table();
 474     _gen.age_table()->merge(local_table);
 475 
 476     // Inform old gen that we're done.
 477     _next_gen.par_promote_alloc_done(i);
 478     _next_gen.par_oop_since_save_marks_iterate_done(i);
 479   }
 480 
 481   if (UseConcMarkSweepGC && ParallelGCThreads > 0) {
 482     // We need to call this even when ResizeOldPLAB is disabled
 483     // so as to avoid breaking some asserts. While we may be able
 484     // to avoid this by reorganizing the code a bit, I am loathe
 485     // to do that unless we find cases where ergo leads to bad
 486     // performance.
 487     CFLS_LAB::compute_desired_plab_size();
 488   }
 489 }
 490 
 491 ParScanClosure::ParScanClosure(ParNewGeneration* g,
 492                                ParScanThreadState* par_scan_state) :
 493   OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
 494 {
 495   assert(_g->level() == 0, "Optimized for youngest generation");
 496   _boundary = _g->reserved().end();
 497 }
 498 
 499 void ParScanWithBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, false); }
 500 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
 501 
 502 void ParScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, false); }
 503 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
 504 
 505 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, true, true); }
 506 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
 507 
 508 void ParRootScanWithoutBarrierClosure::do_oop(oop* p)       { ParScanClosure::do_oop_work(p, false, true); }
 509 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
 510 
 511 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
 512                                              ParScanThreadState* par_scan_state)
 513   : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
 514 {}
 515 
 516 void ParScanWeakRefClosure::do_oop(oop* p)       { ParScanWeakRefClosure::do_oop_work(p); }
 517 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
 518 
 519 #ifdef WIN32
 520 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
 521 #endif
 522 
 523 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
 524     ParScanThreadState* par_scan_state_,
 525     ParScanWithoutBarrierClosure* to_space_closure_,
 526     ParScanWithBarrierClosure* old_gen_closure_,
 527     ParRootScanWithoutBarrierClosure* to_space_root_closure_,
 528     ParNewGeneration* par_gen_,
 529     ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
 530     ObjToScanQueueSet* task_queues_,
 531     ParallelTaskTerminator* terminator_) :
 532 
 533     _par_scan_state(par_scan_state_),
 534     _to_space_closure(to_space_closure_),
 535     _old_gen_closure(old_gen_closure_),
 536     _to_space_root_closure(to_space_root_closure_),
 537     _old_gen_root_closure(old_gen_root_closure_),
 538     _par_gen(par_gen_),
 539     _task_queues(task_queues_),
 540     _terminator(terminator_)
 541 {}
 542 
 543 void ParEvacuateFollowersClosure::do_void() {
 544   ObjToScanQueue* work_q = par_scan_state()->work_queue();
 545 
 546   while (true) {
 547 
 548     // Scan to-space and old-gen objs until we run out of both.
 549     oop obj_to_scan;
 550     par_scan_state()->trim_queues(0);
 551 
 552     // We have no local work, attempt to steal from other threads.
 553 
 554     // attempt to steal work from promoted.
 555     if (task_queues()->steal(par_scan_state()->thread_num(),
 556                              par_scan_state()->hash_seed(),
 557                              obj_to_scan)) {
 558       bool res = work_q->push(obj_to_scan);
 559       assert(res, "Empty queue should have room for a push.");
 560 
 561       //   if successful, goto Start.
 562       continue;
 563 
 564       // try global overflow list.
 565     } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
 566       continue;
 567     }
 568 
 569     // Otherwise, offer termination.
 570     par_scan_state()->start_term_time();
 571     if (terminator()->offer_termination()) break;
 572     par_scan_state()->end_term_time();
 573   }
 574   assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
 575          "Broken overflow list?");
 576   // Finish the last termination pause.
 577   par_scan_state()->end_term_time();
 578 }
 579 
 580 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen,
 581                 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
 582     AbstractGangTask("ParNewGeneration collection"),
 583     _gen(gen), _next_gen(next_gen),
 584     _young_old_boundary(young_old_boundary),
 585     _state_set(state_set)
 586   {}
 587 
 588 // Reset the terminator for the given number of
 589 // active threads.
 590 void ParNewGenTask::set_for_termination(int active_workers) {
 591   _state_set->reset(active_workers, _gen->promotion_failed());
 592   // Should the heap be passed in?  There's only 1 for now so
 593   // grab it instead.
 594   GenCollectedHeap* gch = GenCollectedHeap::heap();
 595   gch->set_n_termination(active_workers);
 596 }
 597 
 598 void ParNewGenTask::work(uint worker_id) {
 599   GenCollectedHeap* gch = GenCollectedHeap::heap();
 600   // Since this is being done in a separate thread, need new resource
 601   // and handle marks.
 602   ResourceMark rm;
 603   HandleMark hm;
 604   // We would need multiple old-gen queues otherwise.
 605   assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
 606 
 607   Generation* old_gen = gch->next_gen(_gen);
 608 
 609   ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
 610   assert(_state_set->is_valid(worker_id), "Should not have been called");
 611 
 612   par_scan_state.set_young_old_boundary(_young_old_boundary);
 613 
 614   KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
 615                                       gch->rem_set()->klass_rem_set());
 616 
 617   int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_ScavengeCodeCache;
 618 
 619   par_scan_state.start_strong_roots();
 620   gch->gen_process_strong_roots(_gen->level(),
 621                                 true,  // Process younger gens, if any,
 622                                        // as strong roots.
 623                                 false, // no scope; this is parallel code
 624                                 SharedHeap::ScanningOption(so),
 625                                 &par_scan_state.to_space_root_closure(),
 626                                 &par_scan_state.older_gen_closure(),
 627                                 &klass_scan_closure);
 628   par_scan_state.end_strong_roots();
 629 
 630   // "evacuate followers".
 631   par_scan_state.evacuate_followers_closure().do_void();
 632 }
 633 
 634 #ifdef _MSC_VER
 635 #pragma warning( push )
 636 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 637 #endif
 638 ParNewGeneration::
 639 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)
 640   : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
 641   _overflow_list(NULL),
 642   _is_alive_closure(this),
 643   _plab_stats(YoungPLABSize, PLABWeight)
 644 {
 645   NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
 646   NOT_PRODUCT(_num_par_pushes = 0;)
 647   _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
 648   guarantee(_task_queues != NULL, "task_queues allocation failure.");
 649 
 650   for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
 651     ObjToScanQueue *q = new ObjToScanQueue();
 652     guarantee(q != NULL, "work_queue Allocation failure.");
 653     _task_queues->register_queue(i1, q);
 654   }
 655 
 656   for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
 657     _task_queues->queue(i2)->initialize();
 658 
 659   _overflow_stacks = NULL;
 660   if (ParGCUseLocalOverflow) {
 661 
 662     // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
 663     // with ','
 664     typedef Stack<oop, mtGC> GCOopStack;
 665 
 666     _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
 667     for (size_t i = 0; i < ParallelGCThreads; ++i) {
 668       new (_overflow_stacks + i) Stack<oop, mtGC>();
 669     }
 670   }
 671 
 672   if (UsePerfData) {
 673     EXCEPTION_MARK;
 674     ResourceMark rm;
 675 
 676     const char* cname =
 677          PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
 678     PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
 679                                      ParallelGCThreads, CHECK);
 680   }
 681 }
 682 #ifdef _MSC_VER
 683 #pragma warning( pop )
 684 #endif
 685 
 686 // ParNewGeneration::
 687 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
 688   DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
 689 
 690 template <class T>
 691 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
 692 #ifdef ASSERT
 693   {
 694     assert(!oopDesc::is_null(*p), "expected non-null ref");
 695     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 696     // We never expect to see a null reference being processed
 697     // as a weak reference.
 698     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 699   }
 700 #endif // ASSERT
 701 
 702   _par_cl->do_oop_nv(p);
 703 
 704   if (Universe::heap()->is_in_reserved(p)) {
 705     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 706     _rs->write_ref_field_gc_par(p, obj);
 707   }
 708 }
 709 
 710 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p)       { ParKeepAliveClosure::do_oop_work(p); }
 711 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
 712 
 713 // ParNewGeneration::
 714 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
 715   DefNewGeneration::KeepAliveClosure(cl) {}
 716 
 717 template <class T>
 718 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
 719 #ifdef ASSERT
 720   {
 721     assert(!oopDesc::is_null(*p), "expected non-null ref");
 722     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 723     // We never expect to see a null reference being processed
 724     // as a weak reference.
 725     assert(obj->is_oop(), "expected an oop while scanning weak refs");
 726   }
 727 #endif // ASSERT
 728 
 729   _cl->do_oop_nv(p);
 730 
 731   if (Universe::heap()->is_in_reserved(p)) {
 732     oop obj = oopDesc::load_decode_heap_oop_not_null(p);
 733     _rs->write_ref_field_gc_par(p, obj);
 734   }
 735 }
 736 
 737 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p)       { KeepAliveClosure::do_oop_work(p); }
 738 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
 739 
 740 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
 741   T heap_oop = oopDesc::load_heap_oop(p);
 742   if (!oopDesc::is_null(heap_oop)) {
 743     oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
 744     if ((HeapWord*)obj < _boundary) {
 745       assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
 746       oop new_obj = obj->is_forwarded()
 747                       ? obj->forwardee()
 748                       : _g->DefNewGeneration::copy_to_survivor_space(obj);
 749       oopDesc::encode_store_heap_oop_not_null(p, new_obj);
 750     }
 751     if (_gc_barrier) {
 752       // If p points to a younger generation, mark the card.
 753       if ((HeapWord*)obj < _gen_boundary) {
 754         _rs->write_ref_field_gc_par(p, obj);
 755       }
 756     }
 757   }
 758 }
 759 
 760 void ScanClosureWithParBarrier::do_oop(oop* p)       { ScanClosureWithParBarrier::do_oop_work(p); }
 761 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
 762 
 763 class ParNewRefProcTaskProxy: public AbstractGangTask {
 764   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
 765 public:
 766   ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
 767                          Generation& next_gen,
 768                          HeapWord* young_old_boundary,
 769                          ParScanThreadStateSet& state_set);
 770 
 771 private:
 772   virtual void work(uint worker_id);
 773   virtual void set_for_termination(int active_workers) {
 774     _state_set.terminator()->reset_for_reuse(active_workers);
 775   }
 776 private:
 777   ParNewGeneration&      _gen;
 778   ProcessTask&           _task;
 779   Generation&            _next_gen;
 780   HeapWord*              _young_old_boundary;
 781   ParScanThreadStateSet& _state_set;
 782 };
 783 
 784 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
 785     ProcessTask& task, ParNewGeneration& gen,
 786     Generation& next_gen,
 787     HeapWord* young_old_boundary,
 788     ParScanThreadStateSet& state_set)
 789   : AbstractGangTask("ParNewGeneration parallel reference processing"),
 790     _gen(gen),
 791     _task(task),
 792     _next_gen(next_gen),
 793     _young_old_boundary(young_old_boundary),
 794     _state_set(state_set)
 795 {
 796 }
 797 
 798 void ParNewRefProcTaskProxy::work(uint worker_id)
 799 {
 800   ResourceMark rm;
 801   HandleMark hm;
 802   ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
 803   par_scan_state.set_young_old_boundary(_young_old_boundary);
 804   _task.work(worker_id, par_scan_state.is_alive_closure(),
 805              par_scan_state.keep_alive_closure(),
 806              par_scan_state.evacuate_followers_closure());
 807 }
 808 
 809 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
 810   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
 811   EnqueueTask& _task;
 812 
 813 public:
 814   ParNewRefEnqueueTaskProxy(EnqueueTask& task)
 815     : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
 816       _task(task)
 817   { }
 818 
 819   virtual void work(uint worker_id)
 820   {
 821     _task.work(worker_id);
 822   }
 823 };
 824 
 825 
 826 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
 827 {
 828   GenCollectedHeap* gch = GenCollectedHeap::heap();
 829   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 830          "not a generational heap");
 831   FlexibleWorkGang* workers = gch->workers();
 832   assert(workers != NULL, "Need parallel worker threads.");
 833   _state_set.reset(workers->active_workers(), _generation.promotion_failed());
 834   ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
 835                                  _generation.reserved().end(), _state_set);
 836   workers->run_task(&rp_task);
 837   _state_set.reset(0 /* bad value in debug if not reset */,
 838                    _generation.promotion_failed());
 839 }
 840 
 841 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
 842 {
 843   GenCollectedHeap* gch = GenCollectedHeap::heap();
 844   FlexibleWorkGang* workers = gch->workers();
 845   assert(workers != NULL, "Need parallel worker threads.");
 846   ParNewRefEnqueueTaskProxy enq_task(task);
 847   workers->run_task(&enq_task);
 848 }
 849 
 850 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
 851 {
 852   _state_set.flush();
 853   GenCollectedHeap* gch = GenCollectedHeap::heap();
 854   gch->set_par_threads(0);  // 0 ==> non-parallel.
 855   gch->save_marks();
 856 }
 857 
 858 ScanClosureWithParBarrier::
 859 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
 860   ScanClosure(g, gc_barrier) {}
 861 
 862 EvacuateFollowersClosureGeneral::
 863 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
 864                                 OopsInGenClosure* cur,
 865                                 OopsInGenClosure* older) :
 866   _gch(gch), _level(level),
 867   _scan_cur_or_nonheap(cur), _scan_older(older)
 868 {}
 869 
 870 void EvacuateFollowersClosureGeneral::do_void() {
 871   do {
 872     // Beware: this call will lead to closure applications via virtual
 873     // calls.
 874     _gch->oop_since_save_marks_iterate(_level,
 875                                        _scan_cur_or_nonheap,
 876                                        _scan_older);
 877   } while (!_gch->no_allocs_since_save_marks(_level));
 878 }
 879 
 880 
 881 // A Generation that does parallel young-gen collection.
 882 
 883 bool ParNewGeneration::_avoid_promotion_undo = false;
 884 
 885 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set, ParNewTracer& gc_tracer) {
 886   assert(_promo_failure_scan_stack.is_empty(), "post condition");
 887   _promo_failure_scan_stack.clear(true); // Clear cached segments.
 888 
 889   remove_forwarding_pointers();
 890   if (PrintGCDetails) {
 891     gclog_or_tty->print(" (promotion failed)");
 892   }
 893   // All the spaces are in play for mark-sweep.
 894   swap_spaces();  // Make life simpler for CMS || rescan; see 6483690.
 895   from()->set_next_compaction_space(to());
 896   gch->set_incremental_collection_failed();
 897   // Inform the next generation that a promotion failure occurred.
 898   _next_gen->promotion_failure_occurred();
 899 
 900   // Trace promotion failure in the parallel GC threads
 901   thread_state_set.trace_promotion_failed(gc_tracer);
 902   // Single threaded code may have reported promotion failure to the global state
 903   if (_promotion_failed_info.has_failed()) {
 904     gc_tracer.report_promotion_failed(_promotion_failed_info);
 905   }
 906   // Reset the PromotionFailureALot counters.
 907   NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
 908 }
 909 
 910 void ParNewGeneration::collect(bool   full,
 911                                bool   clear_all_soft_refs,
 912                                size_t size,
 913                                bool   is_tlab) {
 914   assert(full || size > 0, "otherwise we don't want to collect");
 915 
 916   GenCollectedHeap* gch = GenCollectedHeap::heap();
 917 
 918   _gc_timer->register_gc_start();
 919 
 920   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 921     "not a CMS generational heap");
 922   AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
 923   FlexibleWorkGang* workers = gch->workers();
 924   assert(workers != NULL, "Need workgang for parallel work");
 925   int active_workers =
 926       AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
 927                                    workers->active_workers(),
 928                                    Threads::number_of_non_daemon_threads());
 929   workers->set_active_workers(active_workers);
 930   assert(gch->n_gens() == 2,
 931          "Par collection currently only works with single older gen.");
 932   _next_gen = gch->next_gen(this);
 933   // Do we have to avoid promotion_undo?
 934   if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) {
 935     set_avoid_promotion_undo(true);
 936   }
 937 
 938   // If the next generation is too full to accommodate worst-case promotion
 939   // from this generation, pass on collection; let the next generation
 940   // do it.
 941   if (!collection_attempt_is_safe()) {
 942     gch->set_incremental_collection_failed();  // slight lie, in that we did not even attempt one
 943     return;
 944   }
 945   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 946 
 947   ParNewTracer gc_tracer;
 948   gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
 949   gch->trace_heap_before_gc(&gc_tracer);
 950 
 951   init_assuming_no_promotion_failure();
 952 
 953   if (UseAdaptiveSizePolicy) {
 954     set_survivor_overflow(false);
 955     size_policy->minor_collection_begin();
 956   }
 957 
 958   GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
 959   // Capture heap used before collection (for printing).
 960   size_t gch_prev_used = gch->used();
 961 
 962   SpecializationStats::clear();
 963 
 964   age_table()->clear();
 965   to()->clear(SpaceDecorator::Mangle);
 966 
 967   gch->save_marks();
 968   assert(workers != NULL, "Need parallel worker threads.");
 969   int n_workers = active_workers;
 970 
 971   // Set the correct parallelism (number of queues) in the reference processor
 972   ref_processor()->set_active_mt_degree(n_workers);
 973 
 974   // Always set the terminator for the active number of workers
 975   // because only those workers go through the termination protocol.
 976   ParallelTaskTerminator _term(n_workers, task_queues());
 977   ParScanThreadStateSet thread_state_set(workers->active_workers(),
 978                                          *to(), *this, *_next_gen, *task_queues(),
 979                                          _overflow_stacks, desired_plab_sz(), _term);
 980 
 981   ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
 982   gch->set_par_threads(n_workers);
 983   gch->rem_set()->prepare_for_younger_refs_iterate(true);
 984   // It turns out that even when we're using 1 thread, doing the work in a
 985   // separate thread causes wide variance in run times.  We can't help this
 986   // in the multi-threaded case, but we special-case n=1 here to get
 987   // repeatable measurements of the 1-thread overhead of the parallel code.
 988   if (n_workers > 1) {
 989     GenCollectedHeap::StrongRootsScope srs(gch);
 990     workers->run_task(&tsk);
 991   } else {
 992     GenCollectedHeap::StrongRootsScope srs(gch);
 993     tsk.work(0);
 994   }
 995   thread_state_set.reset(0 /* Bad value in debug if not reset */,
 996                          promotion_failed());
 997 
 998   // Process (weak) reference objects found during scavenge.
 999   ReferenceProcessor* rp = ref_processor();
1000   IsAliveClosure is_alive(this);
1001   ScanWeakRefClosure scan_weak_ref(this);
1002   KeepAliveClosure keep_alive(&scan_weak_ref);
1003   ScanClosure               scan_without_gc_barrier(this, false);
1004   ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
1005   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
1006   EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
1007     &scan_without_gc_barrier, &scan_with_gc_barrier);
1008   rp->setup_policy(clear_all_soft_refs);
1009   // Can  the mt_degree be set later (at run_task() time would be best)?
1010   rp->set_active_mt_degree(active_workers);
1011   ReferenceProcessorStats stats;
1012   if (rp->processing_is_mt()) {
1013     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1014     stats = rp->process_discovered_references(&is_alive, &keep_alive,
1015                                               &evacuate_followers, &task_executor,
1016                                               _gc_timer);
1017   } else {
1018     thread_state_set.flush();
1019     gch->set_par_threads(0);  // 0 ==> non-parallel.
1020     gch->save_marks();
1021     stats = rp->process_discovered_references(&is_alive, &keep_alive,
1022                                               &evacuate_followers, NULL,
1023                                               _gc_timer);
1024   }
1025   gc_tracer.report_gc_reference_stats(stats);
1026   if (!promotion_failed()) {
1027     // Swap the survivor spaces.
1028     eden()->clear(SpaceDecorator::Mangle);
1029     from()->clear(SpaceDecorator::Mangle);
1030     if (ZapUnusedHeapArea) {
1031       // This is now done here because of the piece-meal mangling which
1032       // can check for valid mangling at intermediate points in the
1033       // collection(s).  When a minor collection fails to collect
1034       // sufficient space resizing of the young generation can occur
1035       // an redistribute the spaces in the young generation.  Mangle
1036       // here so that unzapped regions don't get distributed to
1037       // other spaces.
1038       to()->mangle_unused_area();
1039     }
1040     swap_spaces();
1041 
1042     // A successful scavenge should restart the GC time limit count which is
1043     // for full GC's.
1044     size_policy->reset_gc_overhead_limit_count();
1045 
1046     assert(to()->is_empty(), "to space should be empty now");
1047 
1048     adjust_desired_tenuring_threshold();
1049   } else {
1050     handle_promotion_failed(gch, thread_state_set, gc_tracer);
1051   }
1052   // set new iteration safe limit for the survivor spaces
1053   from()->set_concurrent_iteration_safe_limit(from()->top());
1054   to()->set_concurrent_iteration_safe_limit(to()->top());
1055 
1056   if (ResizePLAB) {
1057     plab_stats()->adjust_desired_plab_sz(n_workers);
1058   }
1059 
1060   if (PrintGC && !PrintGCDetails) {
1061     gch->print_heap_change(gch_prev_used);
1062   }
1063 
1064   if (PrintGCDetails && ParallelGCVerbose) {
1065     TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
1066     TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
1067   }
1068 
1069   if (UseAdaptiveSizePolicy) {
1070     size_policy->minor_collection_end(gch->gc_cause());
1071     size_policy->avg_survived()->sample(from()->used());
1072   }
1073 
1074   // We need to use a monotonically non-decreasing time in ms
1075   // or we will see time-warp warnings and os::javaTimeMillis()
1076   // does not guarantee monotonicity.
1077   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1078   update_time_of_last_gc(now);
1079 
1080   SpecializationStats::print();
1081 
1082   rp->set_enqueuing_is_done(true);
1083   if (rp->processing_is_mt()) {
1084     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1085     rp->enqueue_discovered_references(&task_executor);
1086   } else {
1087     rp->enqueue_discovered_references(NULL);
1088   }
1089   rp->verify_no_references_recorded();
1090 
1091   gch->trace_heap_after_gc(&gc_tracer);
1092   gc_tracer.report_tenuring_threshold(tenuring_threshold());
1093 
1094   _gc_timer->register_gc_end();
1095 
1096   gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1097 }
1098 
1099 static int sum;
1100 void ParNewGeneration::waste_some_time() {
1101   for (int i = 0; i < 100; i++) {
1102     sum += i;
1103   }
1104 }
1105 
1106 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1107 
1108 // Because of concurrency, there are times where an object for which
1109 // "is_forwarded()" is true contains an "interim" forwarding pointer
1110 // value.  Such a value will soon be overwritten with a real value.
1111 // This method requires "obj" to have a forwarding pointer, and waits, if
1112 // necessary for a real one to be inserted, and returns it.
1113 
1114 oop ParNewGeneration::real_forwardee(oop obj) {
1115   oop forward_ptr = obj->forwardee();
1116   if (forward_ptr != ClaimedForwardPtr) {
1117     return forward_ptr;
1118   } else {
1119     return real_forwardee_slow(obj);
1120   }
1121 }
1122 
1123 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1124   // Spin-read if it is claimed but not yet written by another thread.
1125   oop forward_ptr = obj->forwardee();
1126   while (forward_ptr == ClaimedForwardPtr) {
1127     waste_some_time();
1128     assert(obj->is_forwarded(), "precondition");
1129     forward_ptr = obj->forwardee();
1130   }
1131   return forward_ptr;
1132 }
1133 
1134 #ifdef ASSERT
1135 bool ParNewGeneration::is_legal_forward_ptr(oop p) {
1136   return
1137     (_avoid_promotion_undo && p == ClaimedForwardPtr)
1138     || Universe::heap()->is_in_reserved(p);
1139 }
1140 #endif
1141 
1142 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1143   if (m->must_be_preserved_for_promotion_failure(obj)) {
1144     // We should really have separate per-worker stacks, rather
1145     // than use locking of a common pair of stacks.
1146     MutexLocker ml(ParGCRareEvent_lock);
1147     preserve_mark(obj, m);
1148   }
1149 }
1150 
1151 // Multiple GC threads may try to promote an object.  If the object
1152 // is successfully promoted, a forwarding pointer will be installed in
1153 // the object in the young generation.  This method claims the right
1154 // to install the forwarding pointer before it copies the object,
1155 // thus avoiding the need to undo the copy as in
1156 // copy_to_survivor_space_avoiding_with_undo.
1157 
1158 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo(
1159         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1160   // In the sequential version, this assert also says that the object is
1161   // not forwarded.  That might not be the case here.  It is the case that
1162   // the caller observed it to be not forwarded at some time in the past.
1163   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1164 
1165   // The sequential code read "old->age()" below.  That doesn't work here,
1166   // since the age is in the mark word, and that might be overwritten with
1167   // a forwarding pointer by a parallel thread.  So we must save the mark
1168   // word in a local and then analyze it.
1169   oopDesc dummyOld;
1170   dummyOld.set_mark(m);
1171   assert(!dummyOld.is_forwarded(),
1172          "should not be called with forwarding pointer mark word.");
1173 
1174   oop new_obj = NULL;
1175   oop forward_ptr;
1176 
1177   // Try allocating obj in to-space (unless too old)
1178   if (dummyOld.age() < tenuring_threshold()) {
1179     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1180     if (new_obj == NULL) {
1181       set_survivor_overflow(true);
1182     }
1183   }
1184 
1185   if (new_obj == NULL) {
1186     // Either to-space is full or we decided to promote
1187     // try allocating obj tenured
1188 
1189     // Attempt to install a null forwarding pointer (atomically),
1190     // to claim the right to install the real forwarding pointer.
1191     forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1192     if (forward_ptr != NULL) {
1193       // someone else beat us to it.
1194         return real_forwardee(old);
1195     }
1196 
1197     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1198                                        old, m, sz);
1199 
1200     if (new_obj == NULL) {
1201       // promotion failed, forward to self
1202       _promotion_failed = true;
1203       new_obj = old;
1204 
1205       preserve_mark_if_necessary(old, m);
1206       par_scan_state->register_promotion_failure(sz);
1207     }
1208 
1209     old->forward_to(new_obj);
1210     forward_ptr = NULL;
1211   } else {
1212     // Is in to-space; do copying ourselves.
1213     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1214     forward_ptr = old->forward_to_atomic(new_obj);
1215     // Restore the mark word copied above.
1216     new_obj->set_mark(m);
1217     // Increment age if obj still in new generation
1218     new_obj->incr_age();
1219     par_scan_state->age_table()->add(new_obj, sz);
1220   }
1221   assert(new_obj != NULL, "just checking");
1222 
1223 #ifndef PRODUCT
1224   // This code must come after the CAS test, or it will print incorrect
1225   // information.
1226   if (TraceScavenge) {
1227     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1228        is_in_reserved(new_obj) ? "copying" : "tenuring",
1229        new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size());
1230   }
1231 #endif
1232 
1233   if (forward_ptr == NULL) {
1234     oop obj_to_push = new_obj;
1235     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1236       // Length field used as index of next element to be scanned.
1237       // Real length can be obtained from real_forwardee()
1238       arrayOop(old)->set_length(0);
1239       obj_to_push = old;
1240       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1241              "push forwarded object");
1242     }
1243     // Push it on one of the queues of to-be-scanned objects.
1244     bool simulate_overflow = false;
1245     NOT_PRODUCT(
1246       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1247         // simulate a stack overflow
1248         simulate_overflow = true;
1249       }
1250     )
1251     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1252       // Add stats for overflow pushes.
1253       if (Verbose && PrintGCDetails) {
1254         gclog_or_tty->print("queue overflow!\n");
1255       }
1256       push_on_overflow_list(old, par_scan_state);
1257       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1258     }
1259 
1260     return new_obj;
1261   }
1262 
1263   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1264   // allocate it?
1265   if (is_in_reserved(new_obj)) {
1266     // Must be in to_space.
1267     assert(to()->is_in_reserved(new_obj), "Checking");
1268     if (forward_ptr == ClaimedForwardPtr) {
1269       // Wait to get the real forwarding pointer value.
1270       forward_ptr = real_forwardee(old);
1271     }
1272     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1273   }
1274 
1275   return forward_ptr;
1276 }
1277 
1278 
1279 // Multiple GC threads may try to promote the same object.  If two
1280 // or more GC threads copy the object, only one wins the race to install
1281 // the forwarding pointer.  The other threads have to undo their copy.
1282 
1283 oop ParNewGeneration::copy_to_survivor_space_with_undo(
1284         ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1285 
1286   // In the sequential version, this assert also says that the object is
1287   // not forwarded.  That might not be the case here.  It is the case that
1288   // the caller observed it to be not forwarded at some time in the past.
1289   assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1290 
1291   // The sequential code read "old->age()" below.  That doesn't work here,
1292   // since the age is in the mark word, and that might be overwritten with
1293   // a forwarding pointer by a parallel thread.  So we must save the mark
1294   // word here, install it in a local oopDesc, and then analyze it.
1295   oopDesc dummyOld;
1296   dummyOld.set_mark(m);
1297   assert(!dummyOld.is_forwarded(),
1298          "should not be called with forwarding pointer mark word.");
1299 
1300   bool failed_to_promote = false;
1301   oop new_obj = NULL;
1302   oop forward_ptr;
1303 
1304   // Try allocating obj in to-space (unless too old)
1305   if (dummyOld.age() < tenuring_threshold()) {
1306     new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1307     if (new_obj == NULL) {
1308       set_survivor_overflow(true);
1309     }
1310   }
1311 
1312   if (new_obj == NULL) {
1313     // Either to-space is full or we decided to promote
1314     // try allocating obj tenured
1315     new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1316                                        old, m, sz);
1317 
1318     if (new_obj == NULL) {
1319       // promotion failed, forward to self
1320       forward_ptr = old->forward_to_atomic(old);
1321       new_obj = old;
1322 
1323       if (forward_ptr != NULL) {
1324         return forward_ptr;   // someone else succeeded
1325       }
1326 
1327       _promotion_failed = true;
1328       failed_to_promote = true;
1329 
1330       preserve_mark_if_necessary(old, m);
1331       par_scan_state->register_promotion_failure(sz);
1332     }
1333   } else {
1334     // Is in to-space; do copying ourselves.
1335     Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1336     // Restore the mark word copied above.
1337     new_obj->set_mark(m);
1338     // Increment age if new_obj still in new generation
1339     new_obj->incr_age();
1340     par_scan_state->age_table()->add(new_obj, sz);
1341   }
1342   assert(new_obj != NULL, "just checking");
1343 
1344 #ifndef PRODUCT
1345   // This code must come after the CAS test, or it will print incorrect
1346   // information.
1347   if (TraceScavenge) {
1348     gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1349        is_in_reserved(new_obj) ? "copying" : "tenuring",
1350        new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size());
1351   }
1352 #endif
1353 
1354   // Now attempt to install the forwarding pointer (atomically).
1355   // We have to copy the mark word before overwriting with forwarding
1356   // ptr, so we can restore it below in the copy.
1357   if (!failed_to_promote) {
1358     forward_ptr = old->forward_to_atomic(new_obj);
1359   }
1360 
1361   if (forward_ptr == NULL) {
1362     oop obj_to_push = new_obj;
1363     if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1364       // Length field used as index of next element to be scanned.
1365       // Real length can be obtained from real_forwardee()
1366       arrayOop(old)->set_length(0);
1367       obj_to_push = old;
1368       assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1369              "push forwarded object");
1370     }
1371     // Push it on one of the queues of to-be-scanned objects.
1372     bool simulate_overflow = false;
1373     NOT_PRODUCT(
1374       if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1375         // simulate a stack overflow
1376         simulate_overflow = true;
1377       }
1378     )
1379     if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1380       // Add stats for overflow pushes.
1381       push_on_overflow_list(old, par_scan_state);
1382       TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1383     }
1384 
1385     return new_obj;
1386   }
1387 
1388   // Oops.  Someone beat us to it.  Undo the allocation.  Where did we
1389   // allocate it?
1390   if (is_in_reserved(new_obj)) {
1391     // Must be in to_space.
1392     assert(to()->is_in_reserved(new_obj), "Checking");
1393     par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1394   } else {
1395     assert(!_avoid_promotion_undo, "Should not be here if avoiding.");
1396     _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(),
1397                                       (HeapWord*)new_obj, sz);
1398   }
1399 
1400   return forward_ptr;
1401 }
1402 
1403 #ifndef PRODUCT
1404 // It's OK to call this multi-threaded;  the worst thing
1405 // that can happen is that we'll get a bunch of closely
1406 // spaced simulated overflows, but that's OK, in fact
1407 // probably good as it would exercise the overflow code
1408 // under contention.
1409 bool ParNewGeneration::should_simulate_overflow() {
1410   if (_overflow_counter-- <= 0) { // just being defensive
1411     _overflow_counter = ParGCWorkQueueOverflowInterval;
1412     return true;
1413   } else {
1414     return false;
1415   }
1416 }
1417 #endif
1418 
1419 // In case we are using compressed oops, we need to be careful.
1420 // If the object being pushed is an object array, then its length
1421 // field keeps track of the "grey boundary" at which the next
1422 // incremental scan will be done (see ParGCArrayScanChunk).
1423 // When using compressed oops, this length field is kept in the
1424 // lower 32 bits of the erstwhile klass word and cannot be used
1425 // for the overflow chaining pointer (OCP below). As such the OCP
1426 // would itself need to be compressed into the top 32-bits in this
1427 // case. Unfortunately, see below, in the event that we have a
1428 // promotion failure, the node to be pushed on the list can be
1429 // outside of the Java heap, so the heap-based pointer compression
1430 // would not work (we would have potential aliasing between C-heap
1431 // and Java-heap pointers). For this reason, when using compressed
1432 // oops, we simply use a worker-thread-local, non-shared overflow
1433 // list in the form of a growable array, with a slightly different
1434 // overflow stack draining strategy. If/when we start using fat
1435 // stacks here, we can go back to using (fat) pointer chains
1436 // (although some performance comparisons would be useful since
1437 // single global lists have their own performance disadvantages
1438 // as we were made painfully aware not long ago, see 6786503).
1439 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1440 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1441   assert(is_in_reserved(from_space_obj), "Should be from this generation");
1442   if (ParGCUseLocalOverflow) {
1443     // In the case of compressed oops, we use a private, not-shared
1444     // overflow stack.
1445     par_scan_state->push_on_overflow_stack(from_space_obj);
1446   } else {
1447     assert(!UseCompressedOops, "Error");
1448     // if the object has been forwarded to itself, then we cannot
1449     // use the klass pointer for the linked list.  Instead we have
1450     // to allocate an oopDesc in the C-Heap and use that for the linked list.
1451     // XXX This is horribly inefficient when a promotion failure occurs
1452     // and should be fixed. XXX FIX ME !!!
1453 #ifndef PRODUCT
1454     Atomic::inc_ptr(&_num_par_pushes);
1455     assert(_num_par_pushes > 0, "Tautology");
1456 #endif
1457     if (from_space_obj->forwardee() == from_space_obj) {
1458       oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1459       listhead->forward_to(from_space_obj);
1460       from_space_obj = listhead;
1461     }
1462     oop observed_overflow_list = _overflow_list;
1463     oop cur_overflow_list;
1464     do {
1465       cur_overflow_list = observed_overflow_list;
1466       if (cur_overflow_list != BUSY) {
1467         from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1468       } else {
1469         from_space_obj->set_klass_to_list_ptr(NULL);
1470       }
1471       observed_overflow_list =
1472         (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1473     } while (cur_overflow_list != observed_overflow_list);
1474   }
1475 }
1476 
1477 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1478   bool res;
1479 
1480   if (ParGCUseLocalOverflow) {
1481     res = par_scan_state->take_from_overflow_stack();
1482   } else {
1483     assert(!UseCompressedOops, "Error");
1484     res = take_from_overflow_list_work(par_scan_state);
1485   }
1486   return res;
1487 }
1488 
1489 
1490 // *NOTE*: The overflow list manipulation code here and
1491 // in CMSCollector:: are very similar in shape,
1492 // except that in the CMS case we thread the objects
1493 // directly into the list via their mark word, and do
1494 // not need to deal with special cases below related
1495 // to chunking of object arrays and promotion failure
1496 // handling.
1497 // CR 6797058 has been filed to attempt consolidation of
1498 // the common code.
1499 // Because of the common code, if you make any changes in
1500 // the code below, please check the CMS version to see if
1501 // similar changes might be needed.
1502 // See CMSCollector::par_take_from_overflow_list() for
1503 // more extensive documentation comments.
1504 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1505   ObjToScanQueue* work_q = par_scan_state->work_queue();
1506   // How many to take?
1507   size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1508                                  (size_t)ParGCDesiredObjsFromOverflowList);
1509 
1510   assert(!UseCompressedOops, "Error");
1511   assert(par_scan_state->overflow_stack() == NULL, "Error");
1512   if (_overflow_list == NULL) return false;
1513 
1514   // Otherwise, there was something there; try claiming the list.
1515   oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1516   // Trim off a prefix of at most objsFromOverflow items
1517   Thread* tid = Thread::current();
1518   size_t spin_count = (size_t)ParallelGCThreads;
1519   size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1520   for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1521     // someone grabbed it before we did ...
1522     // ... we spin for a short while...
1523     os::sleep(tid, sleep_time_millis, false);
1524     if (_overflow_list == NULL) {
1525       // nothing left to take
1526       return false;
1527     } else if (_overflow_list != BUSY) {
1528      // try and grab the prefix
1529      prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1530     }
1531   }
1532   if (prefix == NULL || prefix == BUSY) {
1533      // Nothing to take or waited long enough
1534      if (prefix == NULL) {
1535        // Write back the NULL in case we overwrote it with BUSY above
1536        // and it is still the same value.
1537        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1538      }
1539      return false;
1540   }
1541   assert(prefix != NULL && prefix != BUSY, "Error");
1542   size_t i = 1;
1543   oop cur = prefix;
1544   while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1545     i++; cur = cur->list_ptr_from_klass();
1546   }
1547 
1548   // Reattach remaining (suffix) to overflow list
1549   if (cur->klass_or_null() == NULL) {
1550     // Write back the NULL in lieu of the BUSY we wrote
1551     // above and it is still the same value.
1552     if (_overflow_list == BUSY) {
1553       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1554     }
1555   } else {
1556     assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1557     oop suffix = cur->list_ptr_from_klass();       // suffix will be put back on global list
1558     cur->set_klass_to_list_ptr(NULL);     // break off suffix
1559     // It's possible that the list is still in the empty(busy) state
1560     // we left it in a short while ago; in that case we may be
1561     // able to place back the suffix.
1562     oop observed_overflow_list = _overflow_list;
1563     oop cur_overflow_list = observed_overflow_list;
1564     bool attached = false;
1565     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1566       observed_overflow_list =
1567         (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1568       if (cur_overflow_list == observed_overflow_list) {
1569         attached = true;
1570         break;
1571       } else cur_overflow_list = observed_overflow_list;
1572     }
1573     if (!attached) {
1574       // Too bad, someone else got in in between; we'll need to do a splice.
1575       // Find the last item of suffix list
1576       oop last = suffix;
1577       while (last->klass_or_null() != NULL) {
1578         last = last->list_ptr_from_klass();
1579       }
1580       // Atomically prepend suffix to current overflow list
1581       observed_overflow_list = _overflow_list;
1582       do {
1583         cur_overflow_list = observed_overflow_list;
1584         if (cur_overflow_list != BUSY) {
1585           // Do the splice ...
1586           last->set_klass_to_list_ptr(cur_overflow_list);
1587         } else { // cur_overflow_list == BUSY
1588           last->set_klass_to_list_ptr(NULL);
1589         }
1590         observed_overflow_list =
1591           (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1592       } while (cur_overflow_list != observed_overflow_list);
1593     }
1594   }
1595 
1596   // Push objects on prefix list onto this thread's work queue
1597   assert(prefix != NULL && prefix != BUSY, "program logic");
1598   cur = prefix;
1599   ssize_t n = 0;
1600   while (cur != NULL) {
1601     oop obj_to_push = cur->forwardee();
1602     oop next        = cur->list_ptr_from_klass();
1603     cur->set_klass(obj_to_push->klass());
1604     // This may be an array object that is self-forwarded. In that case, the list pointer
1605     // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1606     if (!is_in_reserved(cur)) {
1607       // This can become a scaling bottleneck when there is work queue overflow coincident
1608       // with promotion failure.
1609       oopDesc* f = cur;
1610       FREE_C_HEAP_ARRAY(oopDesc, f, mtGC);
1611     } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1612       assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1613       obj_to_push = cur;
1614     }
1615     bool ok = work_q->push(obj_to_push);
1616     assert(ok, "Should have succeeded");
1617     cur = next;
1618     n++;
1619   }
1620   TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1621 #ifndef PRODUCT
1622   assert(_num_par_pushes >= n, "Too many pops?");
1623   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1624 #endif
1625   return true;
1626 }
1627 #undef BUSY
1628 
1629 void ParNewGeneration::ref_processor_init() {
1630   if (_ref_processor == NULL) {
1631     // Allocate and initialize a reference processor
1632     _ref_processor =
1633       new ReferenceProcessor(_reserved,                  // span
1634                              ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1635                              (int) ParallelGCThreads,    // mt processing degree
1636                              refs_discovery_is_mt(),     // mt discovery
1637                              (int) ParallelGCThreads,    // mt discovery degree
1638                              refs_discovery_is_atomic(), // atomic_discovery
1639                              NULL);                      // is_alive_non_header
1640   }
1641 }
1642 
1643 const char* ParNewGeneration::name() const {
1644   return "par new generation";
1645 }