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/g1StringDedup.hpp"
28 #include "gc_implementation/g1/g1StringDedupQueue.hpp"
29 #include "memory/gcLocker.hpp"
30 #include "runtime/atomic.inline.hpp"
31 #include "runtime/mutexLocker.hpp"
32 #include "utilities/stack.inline.hpp"
33
34 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
35 const size_t G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
36 const size_t G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
37
38 G1StringDedupQueue::G1StringDedupQueue() :
39 _cursor(0),
40 _cancel(false),
41 _empty(true),
42 _dropped(0) {
43 _nqueues = MAX2(ParallelGCThreads, (size_t)1);
44 _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
45 for (size_t i = 0; i < _nqueues; i++) {
46 new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
47 }
48 }
49
50 G1StringDedupQueue::~G1StringDedupQueue() {
51 ShouldNotReachHere();
52 }
53
54 void G1StringDedupQueue::create() {
55 assert(_queue == NULL, "One string deduplication queue allowed");
56 _queue = new G1StringDedupQueue();
57 }
58
59 void G1StringDedupQueue::wait() {
60 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
61 while (_queue->_empty && !_queue->_cancel) {
62 ml.wait(Mutex::_no_safepoint_check_flag);
63 }
64 }
65
66 void G1StringDedupQueue::cancel_wait() {
67 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
68 _queue->_cancel = true;
69 ml.notify();
70 }
71
72 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
73 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
74 assert(worker_id < _queue->_nqueues, "Invalid queue");
75
76 // Push and notify waiter
77 G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
78 if (!worker_queue.is_full()) {
79 worker_queue.push(java_string);
80 if (_queue->_empty) {
81 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
82 if (_queue->_empty) {
83 // Mark non-empty and notify waiter
84 _queue->_empty = false;
85 ml.notify();
86 }
87 }
88 } else {
89 // Queue is full, drop the string and update the statistics
90 Atomic::inc_ptr(&_queue->_dropped);
91 }
92 }
93
94 oop G1StringDedupQueue::pop() {
95 assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
96 No_Safepoint_Verifier nsv;
97
98 // Try all queues before giving up
99 for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
100 // The cursor indicates where we left of last time
101 G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
102 while (!queue->is_empty()) {
103 oop obj = queue->pop();
104 // The oop we pop can be NULL if it was marked
105 // dead. Just ignore those and pop the next oop.
106 if (obj != NULL) {
107 return obj;
108 }
109 }
110
111 // Try next queue
112 _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
113 }
114
115 // Mark empty
116 _queue->_empty = true;
117
118 return NULL;
119 }
120
121 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
122 // A worker thread first claims a queue, which ensures exclusive
123 // access to that queue, then continues to process it.
124 for (;;) {
125 // Grab next queue to scan
126 size_t queue = cl->claim_queue();
127 if (queue >= _queue->_nqueues) {
128 // End of queues
129 break;
130 }
131
132 // Scan the queue
133 unlink_or_oops_do(cl, queue);
134 }
135 }
136
137 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
138 assert(queue < _queue->_nqueues, "Invalid queue");
139 StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
140 while (!iter.is_empty()) {
141 oop* p = iter.next_addr();
142 if (*p != NULL) {
143 if (cl->is_alive(*p)) {
144 cl->keep_alive(p);
145 } else {
146 // Clear dead reference
147 *p = NULL;
148 }
149 }
150 }
151 }
152
153 void G1StringDedupQueue::print_statistics(outputStream* st) {
154 st->print_cr(
155 " [Queue]\n"
156 " [Dropped: "UINTX_FORMAT"]", _queue->_dropped);
157 }
158
159 void G1StringDedupQueue::verify() {
160 for (size_t i = 0; i < _queue->_nqueues; i++) {
161 StackIterator<oop, mtGC> iter(_queue->_queues[i]);
162 while (!iter.is_empty()) {
163 oop obj = iter.next();
164 if (obj != NULL) {
165 guarantee(Universe::heap()->is_in_reserved(obj), "Object must be on the heap");
166 guarantee(!obj->is_forwarded(), "Object must not be forwarded");
167 guarantee(java_lang_String::is_instance(obj), "Object must be a String");
168 }
169 }
170 }
171 }