1 /*
2 * Copyright (c) 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/javaClasses.hpp"
27 #include "gc_implementation/g1/g1StringDedupQueue.hpp"
28 #include "memory/gcLocker.hpp"
29 #include "runtime/mutexLocker.hpp"
30 #include "utilities/stack.inline.hpp"
31
32 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
33 const size_t G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
34 const size_t G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
35
36 G1StringDedupQueue::G1StringDedupQueue() :
37 _cursor(0),
38 _cancel(false),
39 _empty(true),
40 _dropped(0) {
41 _nqueues = MAX2(ParallelGCThreads, (uintx)1);
42 _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
43 for (size_t i = 0; i < _nqueues; i++) {
44 new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
45 }
46 }
47
48 G1StringDedupQueue::~G1StringDedupQueue() {
49 ShouldNotReachHere();
50 }
51
52 void G1StringDedupQueue::create() {
53 assert(_queue == NULL, "One string deduplication queue allowed");
54 _queue = new G1StringDedupQueue();
55 }
56
57 void G1StringDedupQueue::wait() {
58 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
59 while (_queue->_empty && !_queue->_cancel) {
60 ml.wait(Mutex::_no_safepoint_check_flag);
61 }
62 }
63
64 void G1StringDedupQueue::cancel_wait() {
65 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
66 _queue->_cancel = true;
67 ml.notify();
68 }
69
70 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
71 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
72 assert(worker_id < _queue->_nqueues, "Invalid queue");
73
74 // Push and notify waiter
75 G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
76 if (!worker_queue.is_full()) {
77 worker_queue.push(java_string);
78 if (_queue->_empty) {
79 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
80 if (_queue->_empty) {
81 // Mark non-empty and notify waiter
82 _queue->_empty = false;
83 ml.notify();
84 }
85 }
86 } else {
87 // Queue is full, drop the string and update the statistics
88 Atomic::inc_ptr(&_queue->_dropped);
89 }
90 }
91
92 oop G1StringDedupQueue::pop() {
93 assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
94 No_Safepoint_Verifier nsv;
95
96 // Try all queues before giving up
97 for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
98 // The cursor indicates where we left of last time
99 G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
100 while (!queue->is_empty()) {
101 oop obj = queue->pop();
102 // The oop we pop can be NULL if it was marked
103 // dead. Just ignore those and pop the next oop.
104 if (obj != NULL) {
105 return obj;
106 }
107 }
108
109 // Try next queue
110 _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
111 }
112
113 // Mark empty
114 _queue->_empty = true;
115
116 return NULL;
117 }
118
119 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
120 // A worker thread first claims a queue, which ensures exclusive
121 // access to that queue, then continues to process it.
122 for (;;) {
123 // Grab next queue to scan
124 size_t queue = cl->claim_queue();
125 if (queue >= _queue->_nqueues) {
126 // End of queues
127 break;
128 }
129
130 // Scan the queue
131 unlink_or_oops_do(cl, queue);
132 }
133 }
134
135 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
136 assert(queue < _queue->_nqueues, "Invalid queue");
137 StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
138 while (!iter.is_empty()) {
139 oop* p = iter.next_addr();
140 if (*p != NULL) {
141 if (cl->is_alive(*p)) {
142 cl->keep_alive(p);
143 } else {
144 // Clear dead reference
145 *p = NULL;
146 }
147 }
148 }
149 }
150
151 void G1StringDedupQueue::print_statistics(outputStream* st) {
152 st->print_cr(
153 " [Queue]\n"
154 " [Dropped: "UINTX_FORMAT"]", _queue->_dropped);
155 }
156
157 void G1StringDedupQueue::verify() {
158 for (size_t i = 0; i < _queue->_nqueues; i++) {
159 StackIterator<oop, mtGC> iter(_queue->_queues[i]);
160 while (!iter.is_empty()) {
161 oop obj = iter.next();
162 if (obj != NULL) {
163 guarantee(Universe::heap()->is_in_reserved(obj), "Object must be on the heap");
164 guarantee(!obj->is_forwarded(), "Object must not be forwarded");
165 guarantee(java_lang_String::is_instance(obj), "Object must be a String");
166 }
167 }
168 }
169 }