1/*
2 * Copyright (c) 2014, 2016, 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.hpp"
34#include "runtime/mutexLocker.hpp"
35#include "utilities/stack.inline.hpp"
36
37G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
38const size_t        G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
39const size_t        G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
40
41G1StringDedupQueue::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
53G1StringDedupQueue::~G1StringDedupQueue() {
54  ShouldNotReachHere();
55}
56
57void G1StringDedupQueue::create() {
58  assert(_queue == NULL, "One string deduplication queue allowed");
59  _queue = new G1StringDedupQueue();
60}
61
62void 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
69void G1StringDedupQueue::cancel_wait() {
70  MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
71  _queue->_cancel = true;
72  ml.notify();
73}
74
75void 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
97oop G1StringDedupQueue::pop() {
98  assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
99  NoSafepointVerifier 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
124void 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
140void 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
156void G1StringDedupQueue::print_statistics() {
157  log_debug(gc, stringdedup)("  Queue");
158  log_debug(gc, stringdedup)("    Dropped: " UINTX_FORMAT, _queue->_dropped);
159}
160
161void G1StringDedupQueue::verify() {
162  for (size_t i = 0; i < _queue->_nqueues; i++) {
163    StackIterator<oop, mtGC> iter(_queue->_queues[i]);
164    while (!iter.is_empty()) {
165      oop obj = iter.next();
166      if (obj != NULL) {
167        guarantee(G1CollectedHeap::heap()->is_in_reserved(obj), "Object must be on the heap");
168        guarantee(!obj->is_forwarded(), "Object must not be forwarded");
169        guarantee(java_lang_String::is_instance(obj), "Object must be a String");
170      }
171    }
172  }
173}
174