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comparison src/share/vm/gc_implementation/g1/g1StringDedupQueue.cpp @ 17764:595c0f60d50d

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8029075: String deduplication in G1 Summary: Implementation of JEP 192, http://openjdk.java.net/jeps/192 Reviewed-by: brutisso, tschatzl, coleenp
author pliden
date Tue, 18 Mar 2014 19:07:22 +0100
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children 1772223a25a2
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17763:6e7e363c5a8f 17764:595c0f60d50d
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 _empty(true),
39 _dropped(0) {
40 _nqueues = MAX2(ParallelGCThreads, (size_t)1);
41 _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
42 for (size_t i = 0; i < _nqueues; i++) {
43 new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
44 }
45 }
46
47 G1StringDedupQueue::~G1StringDedupQueue() {
48 ShouldNotReachHere();
49 }
50
51 void G1StringDedupQueue::create() {
52 assert(_queue == NULL, "One string deduplication queue allowed");
53 _queue = new G1StringDedupQueue();
54 }
55
56 void G1StringDedupQueue::wait() {
57 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
58 while (_queue->_empty) {
59 ml.wait(Mutex::_no_safepoint_check_flag);
60 }
61 }
62
63 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
64 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
65 assert(worker_id < _queue->_nqueues, "Invalid queue");
66
67 // Push and notify waiter
68 G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
69 if (!worker_queue.is_full()) {
70 worker_queue.push(java_string);
71 if (_queue->_empty) {
72 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
73 if (_queue->_empty) {
74 // Mark non-empty and notify waiter
75 _queue->_empty = false;
76 ml.notify();
77 }
78 }
79 } else {
80 // Queue is full, drop the string and update the statistics
81 Atomic::inc_ptr(&_queue->_dropped);
82 }
83 }
84
85 oop G1StringDedupQueue::pop() {
86 assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
87 No_Safepoint_Verifier nsv;
88
89 // Try all queues before giving up
90 for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
91 // The cursor indicates where we left of last time
92 G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
93 while (!queue->is_empty()) {
94 oop obj = queue->pop();
95 // The oop we pop can be NULL if it was marked
96 // dead. Just ignore those and pop the next oop.
97 if (obj != NULL) {
98 return obj;
99 }
100 }
101
102 // Try next queue
103 _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
104 }
105
106 // Mark empty
107 _queue->_empty = true;
108
109 return NULL;
110 }
111
112 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
113 // A worker thread first claims a queue, which ensures exclusive
114 // access to that queue, then continues to process it.
115 for (;;) {
116 // Grab next queue to scan
117 size_t queue = cl->claim_queue();
118 if (queue >= _queue->_nqueues) {
119 // End of queues
120 break;
121 }
122
123 // Scan the queue
124 unlink_or_oops_do(cl, queue);
125 }
126 }
127
128 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
129 assert(queue < _queue->_nqueues, "Invalid queue");
130 StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
131 while (!iter.is_empty()) {
132 oop* p = iter.next_addr();
133 if (*p != NULL) {
134 if (cl->is_alive(*p)) {
135 cl->keep_alive(p);
136 } else {
137 // Clear dead reference
138 *p = NULL;
139 }
140 }
141 }
142 }
143
144 void G1StringDedupQueue::print_statistics(outputStream* st) {
145 st->print_cr(
146 " [Queue]\n"
147 " [Dropped: "UINTX_FORMAT"]", _queue->_dropped);
148 }
149
150 void G1StringDedupQueue::verify() {
151 for (size_t i = 0; i < _queue->_nqueues; i++) {
152 StackIterator<oop, mtGC> iter(_queue->_queues[i]);
153 while (!iter.is_empty()) {
154 oop obj = iter.next();
155 if (obj != NULL) {
156 guarantee(Universe::heap()->is_in_reserved(obj), "Object must be on the heap");
157 guarantee(!obj->is_forwarded(), "Object must not be forwarded");
158 guarantee(java_lang_String::is_instance(obj), "Object must be a String");
159 }
160 }
161 }
162 }