1 /*
2 * Copyright (c) 2014, 2015, 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.inline.hpp"
27 #include "gc/g1/g1CollectedHeap.hpp"
28 #include "gc/g1/g1StringDedup.hpp"
29 #include "gc/g1/g1StringDedupQueue.hpp"
30 #include "gc/shared/gcLocker.hpp"
31 #include "logging/log.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/atomic.inline.hpp"
34 #include "runtime/mutexLocker.hpp"
35 #include "utilities/stack.inline.hpp"
36
37 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
38 const size_t G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
39 const size_t G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
40
41 G1StringDedupQueue::G1StringDedupQueue() :
42 _cursor(0),
43 _cancel(false),
44 _empty(true),
45 _dropped(0) {
46 _nqueues = ParallelGCThreads;
47 _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
48 for (size_t i = 0; i < _nqueues; i++) {
49 new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
50 }
51 }
52
53 G1StringDedupQueue::~G1StringDedupQueue() {
54 ShouldNotReachHere();
55 }
56
57 void G1StringDedupQueue::create() {
58 assert(_queue == NULL, "One string deduplication queue allowed");
59 _queue = new G1StringDedupQueue();
60 }
61
62 void G1StringDedupQueue::wait() {
63 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
64 while (_queue->_empty && !_queue->_cancel) {
65 ml.wait(Mutex::_no_safepoint_check_flag);
66 }
67 }
68
69 void G1StringDedupQueue::cancel_wait() {
70 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
71 _queue->_cancel = true;
72 ml.notify();
73 }
74
75 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
76 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
77 assert(worker_id < _queue->_nqueues, "Invalid queue");
78
79 // Push and notify waiter
80 G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
81 if (!worker_queue.is_full()) {
82 worker_queue.push(java_string);
83 if (_queue->_empty) {
84 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
85 if (_queue->_empty) {
86 // Mark non-empty and notify waiter
87 _queue->_empty = false;
88 ml.notify();
89 }
90 }
91 } else {
92 // Queue is full, drop the string and update the statistics
93 Atomic::inc_ptr(&_queue->_dropped);
94 }
95 }
96
97 oop G1StringDedupQueue::pop() {
98 assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
99 No_Safepoint_Verifier nsv;
100
101 // Try all queues before giving up
102 for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
103 // The cursor indicates where we left of last time
104 G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
105 while (!queue->is_empty()) {
106 oop obj = queue->pop();
107 // The oop we pop can be NULL if it was marked
108 // dead. Just ignore those and pop the next oop.
109 if (obj != NULL) {
110 return obj;
111 }
112 }
113
114 // Try next queue
115 _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
116 }
117
118 // Mark empty
119 _queue->_empty = true;
120
121 return NULL;
122 }
123
124 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
125 // A worker thread first claims a queue, which ensures exclusive
126 // access to that queue, then continues to process it.
127 for (;;) {
128 // Grab next queue to scan
129 size_t queue = cl->claim_queue();
130 if (queue >= _queue->_nqueues) {
131 // End of queues
132 break;
133 }
134
135 // Scan the queue
136 unlink_or_oops_do(cl, queue);
137 }
138 }
139
140 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
141 assert(queue < _queue->_nqueues, "Invalid queue");
142 StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
143 while (!iter.is_empty()) {
144 oop* p = iter.next_addr();
145 if (*p != NULL) {
146 if (cl->is_alive(*p)) {
147 cl->keep_alive(p);
148 } else {
149 // Clear dead reference
150 *p = NULL;
151 }
152 }
153 }
154 }
155
156 void G1StringDedupQueue::print_statistics() {
157 log_trace(gc, stringdedup)(
158 " [Queue]\n"
159 " [Dropped: " UINTX_FORMAT "]", _queue->_dropped);
160 }
161
162 void G1StringDedupQueue::verify() {
163 for (size_t i = 0; i < _queue->_nqueues; i++) {
164 StackIterator<oop, mtGC> iter(_queue->_queues[i]);
165 while (!iter.is_empty()) {
166 oop obj = iter.next();
167 if (obj != NULL) {
168 guarantee(G1CollectedHeap::heap()->is_in_reserved(obj), "Object must be on the heap");
169 guarantee(!obj->is_forwarded(), "Object must not be forwarded");
170 guarantee(java_lang_String::is_instance(obj), "Object must be a String");
171 }
172 }
173 }
174 }