1 /*
2 * Copyright (c) 2001, 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 "gc/g1/ptrQueue.hpp"
27 #include "memory/allocation.hpp"
28 #include "memory/allocation.inline.hpp"
29 #include "runtime/mutex.hpp"
30 #include "runtime/mutexLocker.hpp"
31 #include "runtime/thread.inline.hpp"
32
33 PtrQueue::PtrQueue(PtrQueueSet* qset, bool perm, bool active) :
34 _qset(qset), _buf(NULL), _index(0), _sz(0), _active(active),
35 _perm(perm), _lock(NULL)
36 {}
37
38 PtrQueue::~PtrQueue() {
39 assert(_perm || (_buf == NULL), "queue must be flushed before delete");
40 }
41
42 void PtrQueue::flush_impl() {
43 if (!_perm && _buf != NULL) {
44 if (_index == _sz) {
45 // No work to do.
46 qset()->deallocate_buffer(_buf);
47 } else {
48 // We must NULL out the unused entries, then enqueue.
49 for (size_t i = 0; i < _index; i += oopSize) {
50 _buf[byte_index_to_index((int)i)] = NULL;
51 }
52 qset()->enqueue_complete_buffer(_buf);
53 }
54 _buf = NULL;
55 _index = 0;
56 }
57 }
58
59
60 void PtrQueue::enqueue_known_active(void* ptr) {
61 assert(_index <= _sz, "Invariant.");
62 assert(_index == 0 || _buf != NULL, "invariant");
63
64 while (_index == 0) {
65 handle_zero_index();
66 }
67
68 assert(_index > 0, "postcondition");
69 _index -= oopSize;
70 _buf[byte_index_to_index((int)_index)] = ptr;
71 assert(_index <= _sz, "Invariant.");
72 }
73
74 void PtrQueue::locking_enqueue_completed_buffer(void** buf) {
75 assert(_lock->owned_by_self(), "Required.");
76
77 // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before
78 // we acquire DirtyCardQ_CBL_mon inside enqueue_complete_buffer as they
79 // have the same rank and we may get the "possible deadlock" message
80 _lock->unlock();
81
82 qset()->enqueue_complete_buffer(buf);
83 // We must relock only because the caller will unlock, for the normal
84 // case.
85 _lock->lock_without_safepoint_check();
86 }
87
88
89 PtrQueueSet::PtrQueueSet(bool notify_when_complete) :
90 _max_completed_queue(0),
91 _cbl_mon(NULL), _fl_lock(NULL),
92 _notify_when_complete(notify_when_complete),
93 _sz(0),
94 _completed_buffers_head(NULL),
95 _completed_buffers_tail(NULL),
96 _n_completed_buffers(0),
97 _process_completed_threshold(0), _process_completed(false),
98 _buf_free_list(NULL), _buf_free_list_sz(0)
99 {
100 _fl_owner = this;
101 }
102
103 void** PtrQueueSet::allocate_buffer() {
104 assert(_sz > 0, "Didn't set a buffer size.");
105 MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);
106 if (_fl_owner->_buf_free_list != NULL) {
107 void** res = BufferNode::make_buffer_from_node(_fl_owner->_buf_free_list);
108 _fl_owner->_buf_free_list = _fl_owner->_buf_free_list->next();
109 _fl_owner->_buf_free_list_sz--;
110 return res;
111 } else {
112 // Allocate space for the BufferNode in front of the buffer.
113 char *b = NEW_C_HEAP_ARRAY(char, _sz + BufferNode::aligned_size(), mtGC);
114 return BufferNode::make_buffer_from_block(b);
115 }
116 }
117
118 void PtrQueueSet::deallocate_buffer(void** buf) {
119 assert(_sz > 0, "Didn't set a buffer size.");
120 MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);
121 BufferNode *node = BufferNode::make_node_from_buffer(buf);
122 node->set_next(_fl_owner->_buf_free_list);
123 _fl_owner->_buf_free_list = node;
124 _fl_owner->_buf_free_list_sz++;
125 }
126
127 void PtrQueueSet::reduce_free_list() {
128 assert(_fl_owner == this, "Free list reduction is allowed only for the owner");
129 // For now we'll adopt the strategy of deleting half.
130 MutexLockerEx x(_fl_lock, Mutex::_no_safepoint_check_flag);
131 size_t n = _buf_free_list_sz / 2;
132 while (n > 0) {
133 assert(_buf_free_list != NULL, "_buf_free_list_sz must be wrong.");
134 void* b = BufferNode::make_block_from_node(_buf_free_list);
135 _buf_free_list = _buf_free_list->next();
136 FREE_C_HEAP_ARRAY(char, b);
137 _buf_free_list_sz --;
138 n--;
139 }
140 }
141
142 void PtrQueue::handle_zero_index() {
143 assert(_index == 0, "Precondition.");
144
145 // This thread records the full buffer and allocates a new one (while
146 // holding the lock if there is one).
147 if (_buf != NULL) {
148 if (!should_enqueue_buffer()) {
149 assert(_index > 0, "the buffer can only be re-used if it's not full");
150 return;
151 }
152
153 if (_lock) {
154 assert(_lock->owned_by_self(), "Required.");
155
156 // The current PtrQ may be the shared dirty card queue and
157 // may be being manipulated by more than one worker thread
158 // during a pause. Since the enqueueing of the completed
159 // buffer unlocks the Shared_DirtyCardQ_lock more than one
160 // worker thread can 'race' on reading the shared queue attributes
161 // (_buf and _index) and multiple threads can call into this
162 // routine for the same buffer. This will cause the completed
163 // buffer to be added to the CBL multiple times.
164
165 // We "claim" the current buffer by caching value of _buf in
166 // a local and clearing the field while holding _lock. When
167 // _lock is released (while enqueueing the completed buffer)
168 // the thread that acquires _lock will skip this code,
169 // preventing the subsequent the multiple enqueue, and
170 // install a newly allocated buffer below.
171
172 void** buf = _buf; // local pointer to completed buffer
173 _buf = NULL; // clear shared _buf field
174
175 locking_enqueue_completed_buffer(buf); // enqueue completed buffer
176
177 // While the current thread was enqueueing the buffer another thread
178 // may have a allocated a new buffer and inserted it into this pointer
179 // queue. If that happens then we just return so that the current
180 // thread doesn't overwrite the buffer allocated by the other thread
181 // and potentially losing some dirtied cards.
182
183 if (_buf != NULL) return;
184 } else {
185 if (qset()->process_or_enqueue_complete_buffer(_buf)) {
186 // Recycle the buffer. No allocation.
187 _sz = qset()->buffer_size();
188 _index = _sz;
189 return;
190 }
191 }
192 }
193 // Reallocate the buffer
194 _buf = qset()->allocate_buffer();
195 _sz = qset()->buffer_size();
196 _index = _sz;
197 }
198
199 bool PtrQueueSet::process_or_enqueue_complete_buffer(void** buf) {
200 if (Thread::current()->is_Java_thread()) {
201 // We don't lock. It is fine to be epsilon-precise here.
202 if (_max_completed_queue == 0 || _max_completed_queue > 0 &&
203 _n_completed_buffers >= _max_completed_queue + _completed_queue_padding) {
204 bool b = mut_process_buffer(buf);
205 if (b) {
206 // True here means that the buffer hasn't been deallocated and the caller may reuse it.
207 return true;
208 }
209 }
210 }
211 // The buffer will be enqueued. The caller will have to get a new one.
212 enqueue_complete_buffer(buf);
213 return false;
214 }
215
216 void PtrQueueSet::enqueue_complete_buffer(void** buf, size_t index) {
217 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
218 BufferNode* cbn = BufferNode::new_from_buffer(buf);
219 cbn->set_index(index);
220 if (_completed_buffers_tail == NULL) {
221 assert(_completed_buffers_head == NULL, "Well-formedness");
222 _completed_buffers_head = cbn;
223 _completed_buffers_tail = cbn;
224 } else {
225 _completed_buffers_tail->set_next(cbn);
226 _completed_buffers_tail = cbn;
227 }
228 _n_completed_buffers++;
229
230 if (!_process_completed && _process_completed_threshold >= 0 &&
231 _n_completed_buffers >= _process_completed_threshold) {
232 _process_completed = true;
233 if (_notify_when_complete)
234 _cbl_mon->notify();
235 }
236 debug_only(assert_completed_buffer_list_len_correct_locked());
237 }
238
239 int PtrQueueSet::completed_buffers_list_length() {
240 int n = 0;
241 BufferNode* cbn = _completed_buffers_head;
242 while (cbn != NULL) {
243 n++;
244 cbn = cbn->next();
245 }
246 return n;
247 }
248
249 void PtrQueueSet::assert_completed_buffer_list_len_correct() {
250 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
251 assert_completed_buffer_list_len_correct_locked();
252 }
253
254 void PtrQueueSet::assert_completed_buffer_list_len_correct_locked() {
255 guarantee(completed_buffers_list_length() == _n_completed_buffers,
256 "Completed buffer length is wrong.");
257 }
258
259 void PtrQueueSet::set_buffer_size(size_t sz) {
260 assert(_sz == 0 && sz > 0, "Should be called only once.");
261 _sz = sz * oopSize;
262 }
263
264 // Merge lists of buffers. Notify the processing threads.
265 // The source queue is emptied as a result. The queues
266 // must share the monitor.
267 void PtrQueueSet::merge_bufferlists(PtrQueueSet *src) {
268 assert(_cbl_mon == src->_cbl_mon, "Should share the same lock");
269 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
270 if (_completed_buffers_tail == NULL) {
271 assert(_completed_buffers_head == NULL, "Well-formedness");
272 _completed_buffers_head = src->_completed_buffers_head;
273 _completed_buffers_tail = src->_completed_buffers_tail;
274 } else {
275 assert(_completed_buffers_head != NULL, "Well formedness");
276 if (src->_completed_buffers_head != NULL) {
277 _completed_buffers_tail->set_next(src->_completed_buffers_head);
278 _completed_buffers_tail = src->_completed_buffers_tail;
279 }
280 }
281 _n_completed_buffers += src->_n_completed_buffers;
282
283 src->_n_completed_buffers = 0;
284 src->_completed_buffers_head = NULL;
285 src->_completed_buffers_tail = NULL;
286
287 assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||
288 _completed_buffers_head != NULL && _completed_buffers_tail != NULL,
289 "Sanity");
290 }
291
292 void PtrQueueSet::notify_if_necessary() {
293 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
294 if (_n_completed_buffers >= _process_completed_threshold || _max_completed_queue == 0) {
295 _process_completed = true;
296 if (_notify_when_complete)
297 _cbl_mon->notify();
298 }
299 }