1/*
2 * Copyright (c) 2001, 2019, 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/shared/ptrQueue.hpp"
27#include "logging/log.hpp"
28#include "memory/allocation.hpp"
29#include "memory/allocation.inline.hpp"
30#include "runtime/atomic.hpp"
31#include "runtime/mutex.hpp"
32#include "runtime/mutexLocker.hpp"
33#include "runtime/orderAccess.hpp"
34#include "runtime/thread.inline.hpp"
35#include "utilities/globalCounter.inline.hpp"
36
37#include <new>
38
39PtrQueue::PtrQueue(PtrQueueSet* qset, bool active) :
40 _qset(qset),
41 _active(active),
42 _index(0),
43 _capacity_in_bytes(0),
44 _buf(NULL)
45{}
46
47PtrQueue::~PtrQueue() {
48 assert(_buf == NULL, "queue must be flushed before delete");
49}
50
51void PtrQueue::flush_impl() {
52 if (_buf != NULL) {
53 BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
54 if (is_empty()) {
55 // No work to do.
56 qset()->deallocate_buffer(node);
57 } else {
58 qset()->enqueue_completed_buffer(node);
59 }
60 _buf = NULL;
61 set_index(0);
62 }
63}
64
65void PtrQueue::enqueue_known_active(void* ptr) {
66 while (_index == 0) {
67 handle_zero_index();
68 }
69
70 assert(_buf != NULL, "postcondition");
71 assert(index() > 0, "postcondition");
72 assert(index() <= capacity(), "invariant");
73 _index -= _element_size;
74 _buf[index()] = ptr;
75}
76
77void PtrQueue::handle_zero_index() {
78 assert(index() == 0, "precondition");
79
80 if (_buf != NULL) {
81 handle_completed_buffer();
82 } else {
83 // Bootstrapping kludge; lazily initialize capacity. The initial
84 // thread's queues are constructed before the second phase of the
85 // two-phase initialization of the associated qsets. As a result,
86 // we can't initialize _capacity_in_bytes in the queue constructor.
87 if (_capacity_in_bytes == 0) {
88 _capacity_in_bytes = index_to_byte_index(qset()->buffer_size());
89 }
90 allocate_buffer();
91 }
92}
93
94void PtrQueue::allocate_buffer() {
95 _buf = qset()->allocate_buffer();
96 reset();
97}
98
99void PtrQueue::enqueue_completed_buffer() {
100 assert(_buf != NULL, "precondition");
101 BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
102 qset()->enqueue_completed_buffer(node);
103 allocate_buffer();
104}
105
106BufferNode* BufferNode::allocate(size_t size) {
107 size_t byte_size = size * sizeof(void*);
108 void* data = NEW_C_HEAP_ARRAY(char, buffer_offset() + byte_size, mtGC);
109 return new (data) BufferNode;
110}
111
112void BufferNode::deallocate(BufferNode* node) {
113 node->~BufferNode();
114 FREE_C_HEAP_ARRAY(char, node);
115}
116
117BufferNode::Allocator::Allocator(const char* name, size_t buffer_size) :
118 _buffer_size(buffer_size),
119 _pending_list(),
120 _free_list(),
121 _pending_count(0),
122 _free_count(0),
123 _transfer_lock(false)
124{
125 strncpy(_name, name, sizeof(_name) - 1);
126 _name[sizeof(_name) - 1] = '\0';
127}
128
129BufferNode::Allocator::~Allocator() {
130 delete_list(_free_list.pop_all());
131 delete_list(_pending_list.pop_all());
132}
133
134void BufferNode::Allocator::delete_list(BufferNode* list) {
135 while (list != NULL) {
136 BufferNode* next = list->next();
137 DEBUG_ONLY(list->set_next(NULL);)
138 BufferNode::deallocate(list);
139 list = next;
140 }
141}
142
143size_t BufferNode::Allocator::free_count() const {
144 return Atomic::load(&_free_count);
145}
146
147BufferNode* BufferNode::Allocator::allocate() {
148 BufferNode* node;
149 {
150 // Protect against ABA; see release().
151 GlobalCounter::CriticalSection cs(Thread::current());
152 node = _free_list.pop();
153 }
154 if (node == NULL) {
155 node = BufferNode::allocate(_buffer_size);
156 } else {
157 // Decrement count after getting buffer from free list. This, along
158 // with incrementing count before adding to free list, ensures count
159 // never underflows.
160 size_t count = Atomic::sub(1u, &_free_count);
161 assert((count + 1) != 0, "_free_count underflow");
162 }
163 return node;
164}
165
166// To solve the ABA problem for lock-free stack pop, allocate does the
167// pop inside a critical section, and release synchronizes on the
168// critical sections before adding to the _free_list. But we don't
169// want to make every release have to do a synchronize. Instead, we
170// initially place released nodes on the _pending_list, and transfer
171// them to the _free_list in batches. Only one transfer at a time is
172// permitted, with a lock bit to control access to that phase. A
173// transfer takes all the nodes from the _pending_list, synchronizes on
174// the _free_list pops, and then adds the former pending nodes to the
175// _free_list. While that's happening, other threads might be adding
176// other nodes to the _pending_list, to be dealt with by some later
177// transfer.
178void BufferNode::Allocator::release(BufferNode* node) {
179 assert(node != NULL, "precondition");
180 assert(node->next() == NULL, "precondition");
181
182 // Desired minimum transfer batch size. There is relatively little
183 // importance to the specific number. It shouldn't be too big, else
184 // we're wasting space when the release rate is low. If the release
185 // rate is high, we might accumulate more than this before being
186 // able to start a new transfer, but that's okay. Also note that
187 // the allocation rate and the release rate are going to be fairly
188 // similar, due to how the buffers are used.
189 const size_t trigger_transfer = 10;
190
191 // Add to pending list. Update count first so no underflow in transfer.
192 size_t pending_count = Atomic::add(1u, &_pending_count);
193 _pending_list.push(*node);
194 if (pending_count > trigger_transfer) {
195 try_transfer_pending();
196 }
197}
198
199// Try to transfer nodes from _pending_list to _free_list, with a
200// synchronization delay for any in-progress pops from the _free_list,
201// to solve ABA there. Return true if performed a (possibly empty)
202// transfer, false if blocked from doing so by some other thread's
203// in-progress transfer.
204bool BufferNode::Allocator::try_transfer_pending() {
205 // Attempt to claim the lock.
206 if (Atomic::load(&_transfer_lock) || // Skip CAS if likely to fail.
207 Atomic::cmpxchg(true, &_transfer_lock, false)) {
208 return false;
209 }
210 // Have the lock; perform the transfer.
211
212 // Claim all the pending nodes.
213 BufferNode* first = _pending_list.pop_all();
214 if (first != NULL) {
215 // Prepare to add the claimed nodes, and update _pending_count.
216 BufferNode* last = first;
217 size_t count = 1;
218 for (BufferNode* next = first->next(); next != NULL; next = next->next()) {
219 last = next;
220 ++count;
221 }
222 Atomic::sub(count, &_pending_count);
223
224 // Wait for any in-progress pops, to avoid ABA for them.
225 GlobalCounter::write_synchronize();
226
227 // Add synchronized nodes to _free_list.
228 // Update count first so no underflow in allocate().
229 Atomic::add(count, &_free_count);
230 _free_list.prepend(*first, *last);
231 log_trace(gc, ptrqueue, freelist)
232 ("Transferred %s pending to free: " SIZE_FORMAT, name(), count);
233 }
234 OrderAccess::release_store(&_transfer_lock, false);
235 return true;
236}
237
238size_t BufferNode::Allocator::reduce_free_list(size_t remove_goal) {
239 try_transfer_pending();
240 size_t removed = 0;
241 for ( ; removed < remove_goal; ++removed) {
242 BufferNode* node = _free_list.pop();
243 if (node == NULL) break;
244 BufferNode::deallocate(node);
245 }
246 size_t new_count = Atomic::sub(removed, &_free_count);
247 log_debug(gc, ptrqueue, freelist)
248 ("Reduced %s free list by " SIZE_FORMAT " to " SIZE_FORMAT,
249 name(), removed, new_count);
250 return removed;
251}
252
253PtrQueueSet::PtrQueueSet(bool notify_when_complete) :
254 _allocator(NULL),
255 _cbl_mon(NULL),
256 _completed_buffers_head(NULL),
257 _completed_buffers_tail(NULL),
258 _n_completed_buffers(0),
259 _process_completed_buffers_threshold(ProcessCompletedBuffersThresholdNever),
260 _process_completed_buffers(false),
261 _notify_when_complete(notify_when_complete),
262 _all_active(false)
263{}
264
265PtrQueueSet::~PtrQueueSet() {
266 // There are presently only a couple (derived) instances ever
267 // created, and they are permanent, so no harm currently done by
268 // doing nothing here.
269}
270
271void PtrQueueSet::initialize(Monitor* cbl_mon,
272 BufferNode::Allocator* allocator) {
273 assert(cbl_mon != NULL && allocator != NULL, "Init order issue?");
274 _cbl_mon = cbl_mon;
275 _allocator = allocator;
276}
277
278void** PtrQueueSet::allocate_buffer() {
279 BufferNode* node = _allocator->allocate();
280 return BufferNode::make_buffer_from_node(node);
281}
282
283void PtrQueueSet::deallocate_buffer(BufferNode* node) {
284 _allocator->release(node);
285}
286
287void PtrQueueSet::enqueue_completed_buffer(BufferNode* cbn) {
288 MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
289 cbn->set_next(NULL);
290 if (_completed_buffers_tail == NULL) {
291 assert(_completed_buffers_head == NULL, "Well-formedness");
292 _completed_buffers_head = cbn;
293 _completed_buffers_tail = cbn;
294 } else {
295 _completed_buffers_tail->set_next(cbn);
296 _completed_buffers_tail = cbn;
297 }
298 _n_completed_buffers++;
299
300 if (!_process_completed_buffers &&
301 (_n_completed_buffers > _process_completed_buffers_threshold)) {
302 _process_completed_buffers = true;
303 if (_notify_when_complete) {
304 _cbl_mon->notify();
305 }
306 }
307 assert_completed_buffers_list_len_correct_locked();
308}
309
310BufferNode* PtrQueueSet::get_completed_buffer(size_t stop_at) {
311 MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
312
313 if (_n_completed_buffers <= stop_at) {
314 return NULL;
315 }
316
317 assert(_n_completed_buffers > 0, "invariant");
318 assert(_completed_buffers_head != NULL, "invariant");
319 assert(_completed_buffers_tail != NULL, "invariant");
320
321 BufferNode* bn = _completed_buffers_head;
322 _n_completed_buffers--;
323 _completed_buffers_head = bn->next();
324 if (_completed_buffers_head == NULL) {
325 assert(_n_completed_buffers == 0, "invariant");
326 _completed_buffers_tail = NULL;
327 _process_completed_buffers = false;
328 }
329 assert_completed_buffers_list_len_correct_locked();
330 bn->set_next(NULL);
331 return bn;
332}
333
334void PtrQueueSet::abandon_completed_buffers() {
335 BufferNode* buffers_to_delete = NULL;
336 {
337 MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
338 buffers_to_delete = _completed_buffers_head;
339 _completed_buffers_head = NULL;
340 _completed_buffers_tail = NULL;
341 _n_completed_buffers = 0;
342 _process_completed_buffers = false;
343 }
344 while (buffers_to_delete != NULL) {
345 BufferNode* bn = buffers_to_delete;
346 buffers_to_delete = bn->next();
347 bn->set_next(NULL);
348 deallocate_buffer(bn);
349 }
350}
351
352#ifdef ASSERT
353
354void PtrQueueSet::assert_completed_buffers_list_len_correct_locked() {
355 assert_lock_strong(_cbl_mon);
356 size_t n = 0;
357 for (BufferNode* bn = _completed_buffers_head; bn != NULL; bn = bn->next()) {
358 ++n;
359 }
360 assert(n == _n_completed_buffers,
361 "Completed buffer length is wrong: counted: " SIZE_FORMAT
362 ", expected: " SIZE_FORMAT, n, _n_completed_buffers);
363}
364
365#endif // ASSERT
366
367// Merge lists of buffers. Notify the processing threads.
368// The source queue is emptied as a result. The queues
369// must share the monitor.
370void PtrQueueSet::merge_bufferlists(PtrQueueSet *src) {
371 assert(_cbl_mon == src->_cbl_mon, "Should share the same lock");
372 MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
373 if (_completed_buffers_tail == NULL) {
374 assert(_completed_buffers_head == NULL, "Well-formedness");
375 _completed_buffers_head = src->_completed_buffers_head;
376 _completed_buffers_tail = src->_completed_buffers_tail;
377 } else {
378 assert(_completed_buffers_head != NULL, "Well formedness");
379 if (src->_completed_buffers_head != NULL) {
380 _completed_buffers_tail->set_next(src->_completed_buffers_head);
381 _completed_buffers_tail = src->_completed_buffers_tail;
382 }
383 }
384 _n_completed_buffers += src->_n_completed_buffers;
385
386 src->_n_completed_buffers = 0;
387 src->_completed_buffers_head = NULL;
388 src->_completed_buffers_tail = NULL;
389 src->_process_completed_buffers = false;
390
391 assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||
392 _completed_buffers_head != NULL && _completed_buffers_tail != NULL,
393 "Sanity");
394 assert_completed_buffers_list_len_correct_locked();
395}
396
397void PtrQueueSet::notify_if_necessary() {
398 MutexLocker x(_cbl_mon, Mutex::_no_safepoint_check_flag);
399 if (_n_completed_buffers > _process_completed_buffers_threshold) {
400 _process_completed_buffers = true;
401 if (_notify_when_complete)
402 _cbl_mon->notify();
403 }
404}
405