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