1 /*
2 * Copyright (c) 2001, 2010, 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 // Simple TaskQueue stats that are collected by default in debug builds.
26
27 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
28 #define TASKQUEUE_STATS 1
29 #elif !defined(TASKQUEUE_STATS)
30 #define TASKQUEUE_STATS 0
31 #endif
32
33 #if TASKQUEUE_STATS
34 #define TASKQUEUE_STATS_ONLY(code) code
35 #else
36 #define TASKQUEUE_STATS_ONLY(code)
37 #endif // TASKQUEUE_STATS
38
39 #if TASKQUEUE_STATS
40 class TaskQueueStats {
41 public:
42 enum StatId {
43 push, // number of taskqueue pushes
44 pop, // number of taskqueue pops
45 pop_slow, // subset of taskqueue pops that were done slow-path
46 steal_attempt, // number of taskqueue steal attempts
47 steal, // number of taskqueue steals
48 overflow, // number of overflow pushes
49 overflow_max_len, // max length of overflow stack
50 last_stat_id
51 };
52
53 public:
54 inline TaskQueueStats() { reset(); }
55
56 inline void record_push() { ++_stats[push]; }
57 inline void record_pop() { ++_stats[pop]; }
58 inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
59 inline void record_steal(bool success);
60 inline void record_overflow(size_t new_length);
61
62 TaskQueueStats & operator +=(const TaskQueueStats & addend);
63
64 inline size_t get(StatId id) const { return _stats[id]; }
65 inline const size_t* get() const { return _stats; }
66
67 inline void reset();
68
69 // Print the specified line of the header (does not include a line separator).
70 static void print_header(unsigned int line, outputStream* const stream = tty,
71 unsigned int width = 10);
72 // Print the statistics (does not include a line separator).
73 void print(outputStream* const stream = tty, unsigned int width = 10) const;
74
75 DEBUG_ONLY(void verify() const;)
76
77 private:
78 size_t _stats[last_stat_id];
79 static const char * const _names[last_stat_id];
80 };
81
82 void TaskQueueStats::record_steal(bool success) {
83 ++_stats[steal_attempt];
84 if (success) ++_stats[steal];
85 }
86
87 void TaskQueueStats::record_overflow(size_t new_len) {
88 ++_stats[overflow];
89 if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
90 }
91
92 void TaskQueueStats::reset() {
93 memset(_stats, 0, sizeof(_stats));
94 }
95 #endif // TASKQUEUE_STATS
96
97 template <unsigned int N>
98 class TaskQueueSuper: public CHeapObj {
99 protected:
100 // Internal type for indexing the queue; also used for the tag.
101 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
102
103 // The first free element after the last one pushed (mod N).
104 volatile uint _bottom;
105
106 enum { MOD_N_MASK = N - 1 };
107
108 class Age {
109 public:
110 Age(size_t data = 0) { _data = data; }
111 Age(const Age& age) { _data = age._data; }
112 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
113
114 Age get() const volatile { return _data; }
115 void set(Age age) volatile { _data = age._data; }
116
117 idx_t top() const volatile { return _fields._top; }
118 idx_t tag() const volatile { return _fields._tag; }
119
120 // Increment top; if it wraps, increment tag also.
121 void increment() {
122 _fields._top = increment_index(_fields._top);
123 if (_fields._top == 0) ++_fields._tag;
124 }
125
126 Age cmpxchg(const Age new_age, const Age old_age) volatile {
127 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
128 (volatile intptr_t *)&_data,
129 (intptr_t)old_age._data);
130 }
131
132 bool operator ==(const Age& other) const { return _data == other._data; }
133
134 private:
135 struct fields {
136 idx_t _top;
137 idx_t _tag;
138 };
139 union {
140 size_t _data;
141 fields _fields;
142 };
143 };
144
145 volatile Age _age;
146
147 // These both operate mod N.
148 static uint increment_index(uint ind) {
149 return (ind + 1) & MOD_N_MASK;
150 }
151 static uint decrement_index(uint ind) {
152 return (ind - 1) & MOD_N_MASK;
153 }
154
155 // Returns a number in the range [0..N). If the result is "N-1", it should be
156 // interpreted as 0.
157 uint dirty_size(uint bot, uint top) const {
158 return (bot - top) & MOD_N_MASK;
159 }
160
161 // Returns the size corresponding to the given "bot" and "top".
162 uint size(uint bot, uint top) const {
163 uint sz = dirty_size(bot, top);
164 // Has the queue "wrapped", so that bottom is less than top? There's a
165 // complicated special case here. A pair of threads could perform pop_local
166 // and pop_global operations concurrently, starting from a state in which
167 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
168 // and the pop_global in incrementing _top (in which case the pop_global
169 // will be awarded the contested queue element.) The resulting state must
170 // be interpreted as an empty queue. (We only need to worry about one such
171 // event: only the queue owner performs pop_local's, and several concurrent
172 // threads attempting to perform the pop_global will all perform the same
173 // CAS, and only one can succeed.) Any stealing thread that reads after
174 // either the increment or decrement will see an empty queue, and will not
175 // join the competitors. The "sz == -1 || sz == N-1" state will not be
176 // modified by concurrent queues, so the owner thread can reset the state to
177 // _bottom == top so subsequent pushes will be performed normally.
178 return (sz == N - 1) ? 0 : sz;
179 }
180
181 public:
182 TaskQueueSuper() : _bottom(0), _age() {}
183
184 // Return true if the TaskQueue contains/does not contain any tasks.
185 bool peek() const { return _bottom != _age.top(); }
186 bool is_empty() const { return size() == 0; }
187
188 // Return an estimate of the number of elements in the queue.
189 // The "careful" version admits the possibility of pop_local/pop_global
190 // races.
191 uint size() const {
192 return size(_bottom, _age.top());
193 }
194
195 uint dirty_size() const {
196 return dirty_size(_bottom, _age.top());
197 }
198
199 void set_empty() {
200 _bottom = 0;
201 _age.set(0);
202 }
203
204 // Maximum number of elements allowed in the queue. This is two less
205 // than the actual queue size, for somewhat complicated reasons.
206 uint max_elems() const { return N - 2; }
207
208 // Total size of queue.
209 static const uint total_size() { return N; }
210
211 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
212 };
213
214 template<class E, unsigned int N = TASKQUEUE_SIZE>
215 class GenericTaskQueue: public TaskQueueSuper<N> {
216 protected:
217 typedef typename TaskQueueSuper<N>::Age Age;
218 typedef typename TaskQueueSuper<N>::idx_t idx_t;
219
220 using TaskQueueSuper<N>::_bottom;
221 using TaskQueueSuper<N>::_age;
222 using TaskQueueSuper<N>::increment_index;
223 using TaskQueueSuper<N>::decrement_index;
224 using TaskQueueSuper<N>::dirty_size;
225
226 public:
227 using TaskQueueSuper<N>::max_elems;
228 using TaskQueueSuper<N>::size;
229 TASKQUEUE_STATS_ONLY(using TaskQueueSuper<N>::stats;)
230
231 private:
232 // Slow paths for push, pop_local. (pop_global has no fast path.)
233 bool push_slow(E t, uint dirty_n_elems);
234 bool pop_local_slow(uint localBot, Age oldAge);
235
236 public:
237 typedef E element_type;
238
239 // Initializes the queue to empty.
240 GenericTaskQueue();
241
242 void initialize();
243
244 // Push the task "t" on the queue. Returns "false" iff the queue is full.
245 inline bool push(E t);
246
247 // Attempts to claim a task from the "local" end of the queue (the most
248 // recently pushed). If successful, returns true and sets t to the task;
249 // otherwise, returns false (the queue is empty).
250 inline bool pop_local(E& t);
251
252 // Like pop_local(), but uses the "global" end of the queue (the least
253 // recently pushed).
254 bool pop_global(E& t);
255
256 // Delete any resource associated with the queue.
257 ~GenericTaskQueue();
258
259 // apply the closure to all elements in the task queue
260 void oops_do(OopClosure* f);
261
262 private:
263 // Element array.
264 volatile E* _elems;
265 };
266
267 template<class E, unsigned int N>
268 GenericTaskQueue<E, N>::GenericTaskQueue() {
269 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
270 }
271
272 template<class E, unsigned int N>
273 void GenericTaskQueue<E, N>::initialize() {
274 _elems = NEW_C_HEAP_ARRAY(E, N);
275 }
276
277 template<class E, unsigned int N>
278 void GenericTaskQueue<E, N>::oops_do(OopClosure* f) {
279 // tty->print_cr("START OopTaskQueue::oops_do");
280 uint iters = size();
281 uint index = _bottom;
282 for (uint i = 0; i < iters; ++i) {
283 index = decrement_index(index);
284 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
285 // index, &_elems[index], _elems[index]);
286 E* t = (E*)&_elems[index]; // cast away volatility
287 oop* p = (oop*)t;
288 assert((*t)->is_oop_or_null(), "Not an oop or null");
289 f->do_oop(p);
290 }
291 // tty->print_cr("END OopTaskQueue::oops_do");
292 }
293
294 template<class E, unsigned int N>
295 bool GenericTaskQueue<E, N>::push_slow(E t, uint dirty_n_elems) {
296 if (dirty_n_elems == N - 1) {
297 // Actually means 0, so do the push.
298 uint localBot = _bottom;
299 // g++ complains if the volatile result of the assignment is unused.
300 const_cast<E&>(_elems[localBot] = t);
301 OrderAccess::release_store(&_bottom, increment_index(localBot));
302 TASKQUEUE_STATS_ONLY(stats.record_push());
303 return true;
304 }
305 return false;
306 }
307
308 template<class E, unsigned int N>
309 bool GenericTaskQueue<E, N>::pop_local_slow(uint localBot, Age oldAge) {
310 // This queue was observed to contain exactly one element; either this
311 // thread will claim it, or a competing "pop_global". In either case,
312 // the queue will be logically empty afterwards. Create a new Age value
313 // that represents the empty queue for the given value of "_bottom". (We
314 // must also increment "tag" because of the case where "bottom == 1",
315 // "top == 0". A pop_global could read the queue element in that case,
316 // then have the owner thread do a pop followed by another push. Without
317 // the incrementing of "tag", the pop_global's CAS could succeed,
318 // allowing it to believe it has claimed the stale element.)
319 Age newAge((idx_t)localBot, oldAge.tag() + 1);
320 // Perhaps a competing pop_global has already incremented "top", in which
321 // case it wins the element.
322 if (localBot == oldAge.top()) {
323 // No competing pop_global has yet incremented "top"; we'll try to
324 // install new_age, thus claiming the element.
325 Age tempAge = _age.cmpxchg(newAge, oldAge);
326 if (tempAge == oldAge) {
327 // We win.
328 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
329 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
330 return true;
331 }
332 }
333 // We lose; a completing pop_global gets the element. But the queue is empty
334 // and top is greater than bottom. Fix this representation of the empty queue
335 // to become the canonical one.
336 _age.set(newAge);
337 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
338 return false;
339 }
340
341 template<class E, unsigned int N>
342 bool GenericTaskQueue<E, N>::pop_global(E& t) {
343 Age oldAge = _age.get();
344 uint localBot = _bottom;
345 uint n_elems = size(localBot, oldAge.top());
346 if (n_elems == 0) {
347 return false;
348 }
349
350 const_cast<E&>(t = _elems[oldAge.top()]);
351 Age newAge(oldAge);
352 newAge.increment();
353 Age resAge = _age.cmpxchg(newAge, oldAge);
354
355 // Note that using "_bottom" here might fail, since a pop_local might
356 // have decremented it.
357 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
358 return resAge == oldAge;
359 }
360
361 template<class E, unsigned int N>
362 GenericTaskQueue<E, N>::~GenericTaskQueue() {
363 FREE_C_HEAP_ARRAY(E, _elems);
364 }
365
366 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
367 // elements that do not fit in the TaskQueue.
368 //
369 // Three methods from super classes are overridden:
370 //
371 // initialize() - initialize the super classes and create the overflow stack
372 // push() - push onto the task queue or, if that fails, onto the overflow stack
373 // is_empty() - return true if both the TaskQueue and overflow stack are empty
374 //
375 // Note that size() is not overridden--it returns the number of elements in the
376 // TaskQueue, and does not include the size of the overflow stack. This
377 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
378 template<class E, unsigned int N = TASKQUEUE_SIZE>
379 class OverflowTaskQueue: public GenericTaskQueue<E, N>
380 {
381 public:
382 typedef GrowableArray<E> overflow_t;
383 typedef GenericTaskQueue<E, N> taskqueue_t;
384
385 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
386
387 OverflowTaskQueue();
388 ~OverflowTaskQueue();
389 void initialize();
390
391 inline overflow_t* overflow_stack() const { return _overflow_stack; }
392
393 // Push task t onto the queue or onto the overflow stack. Return true.
394 inline bool push(E t);
395
396 // Attempt to pop from the overflow stack; return true if anything was popped.
397 inline bool pop_overflow(E& t);
398
399 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
400 inline bool overflow_empty() const { return overflow_stack()->is_empty(); }
401 inline bool is_empty() const {
402 return taskqueue_empty() && overflow_empty();
403 }
404
405 private:
406 overflow_t* _overflow_stack;
407 };
408
409 template <class E, unsigned int N>
410 OverflowTaskQueue<E, N>::OverflowTaskQueue()
411 {
412 _overflow_stack = NULL;
413 }
414
415 template <class E, unsigned int N>
416 OverflowTaskQueue<E, N>::~OverflowTaskQueue()
417 {
418 if (_overflow_stack != NULL) {
419 delete _overflow_stack;
420 _overflow_stack = NULL;
421 }
422 }
423
424 template <class E, unsigned int N>
425 void OverflowTaskQueue<E, N>::initialize()
426 {
427 taskqueue_t::initialize();
428 assert(_overflow_stack == NULL, "memory leak");
429 _overflow_stack = new (ResourceObj::C_HEAP) GrowableArray<E>(10, true);
430 }
431
432 template <class E, unsigned int N>
433 bool OverflowTaskQueue<E, N>::push(E t)
434 {
435 if (!taskqueue_t::push(t)) {
436 overflow_stack()->push(t);
437 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->length()));
438 }
439 return true;
440 }
441
442 template <class E, unsigned int N>
443 bool OverflowTaskQueue<E, N>::pop_overflow(E& t)
444 {
445 if (overflow_empty()) return false;
446 t = overflow_stack()->pop();
447 return true;
448 }
449
450 class TaskQueueSetSuper: public CHeapObj {
451 protected:
452 static int randomParkAndMiller(int* seed0);
453 public:
454 // Returns "true" if some TaskQueue in the set contains a task.
455 virtual bool peek() = 0;
456 };
457
458 template<class T>
459 class GenericTaskQueueSet: public TaskQueueSetSuper {
460 private:
461 uint _n;
462 T** _queues;
463
464 public:
465 typedef typename T::element_type E;
466
467 GenericTaskQueueSet(int n) : _n(n) {
468 typedef T* GenericTaskQueuePtr;
469 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n);
470 for (int i = 0; i < n; i++) {
471 _queues[i] = NULL;
472 }
473 }
474
475 bool steal_1_random(uint queue_num, int* seed, E& t);
476 bool steal_best_of_2(uint queue_num, int* seed, E& t);
477 bool steal_best_of_all(uint queue_num, int* seed, E& t);
478
479 void register_queue(uint i, T* q);
480
481 T* queue(uint n);
482
483 // The thread with queue number "queue_num" (and whose random number seed is
484 // at "seed") is trying to steal a task from some other queue. (It may try
485 // several queues, according to some configuration parameter.) If some steal
486 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
487 // false.
488 bool steal(uint queue_num, int* seed, E& t);
489
490 bool peek();
491 };
492
493 template<class T> void
494 GenericTaskQueueSet<T>::register_queue(uint i, T* q) {
495 assert(i < _n, "index out of range.");
496 _queues[i] = q;
497 }
498
499 template<class T> T*
500 GenericTaskQueueSet<T>::queue(uint i) {
501 return _queues[i];
502 }
503
504 template<class T> bool
505 GenericTaskQueueSet<T>::steal(uint queue_num, int* seed, E& t) {
506 for (uint i = 0; i < 2 * _n; i++) {
507 if (steal_best_of_2(queue_num, seed, t)) {
508 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
509 return true;
510 }
511 }
512 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
513 return false;
514 }
515
516 template<class T> bool
517 GenericTaskQueueSet<T>::steal_best_of_all(uint queue_num, int* seed, E& t) {
518 if (_n > 2) {
519 int best_k;
520 uint best_sz = 0;
521 for (uint k = 0; k < _n; k++) {
522 if (k == queue_num) continue;
523 uint sz = _queues[k]->size();
524 if (sz > best_sz) {
525 best_sz = sz;
526 best_k = k;
527 }
528 }
529 return best_sz > 0 && _queues[best_k]->pop_global(t);
530 } else if (_n == 2) {
531 // Just try the other one.
532 int k = (queue_num + 1) % 2;
533 return _queues[k]->pop_global(t);
534 } else {
535 assert(_n == 1, "can't be zero.");
536 return false;
537 }
538 }
539
540 template<class T> bool
541 GenericTaskQueueSet<T>::steal_1_random(uint queue_num, int* seed, E& t) {
542 if (_n > 2) {
543 uint k = queue_num;
544 while (k == queue_num) k = randomParkAndMiller(seed) % _n;
545 return _queues[2]->pop_global(t);
546 } else if (_n == 2) {
547 // Just try the other one.
548 int k = (queue_num + 1) % 2;
549 return _queues[k]->pop_global(t);
550 } else {
551 assert(_n == 1, "can't be zero.");
552 return false;
553 }
554 }
555
556 template<class T> bool
557 GenericTaskQueueSet<T>::steal_best_of_2(uint queue_num, int* seed, E& t) {
558 if (_n > 2) {
559 uint k1 = queue_num;
560 while (k1 == queue_num) k1 = randomParkAndMiller(seed) % _n;
561 uint k2 = queue_num;
562 while (k2 == queue_num || k2 == k1) k2 = randomParkAndMiller(seed) % _n;
563 // Sample both and try the larger.
564 uint sz1 = _queues[k1]->size();
565 uint sz2 = _queues[k2]->size();
566 if (sz2 > sz1) return _queues[k2]->pop_global(t);
567 else return _queues[k1]->pop_global(t);
568 } else if (_n == 2) {
569 // Just try the other one.
570 uint k = (queue_num + 1) % 2;
571 return _queues[k]->pop_global(t);
572 } else {
573 assert(_n == 1, "can't be zero.");
574 return false;
575 }
576 }
577
578 template<class T>
579 bool GenericTaskQueueSet<T>::peek() {
580 // Try all the queues.
581 for (uint j = 0; j < _n; j++) {
582 if (_queues[j]->peek())
583 return true;
584 }
585 return false;
586 }
587
588 // When to terminate from the termination protocol.
589 class TerminatorTerminator: public CHeapObj {
590 public:
591 virtual bool should_exit_termination() = 0;
592 };
593
594 // A class to aid in the termination of a set of parallel tasks using
595 // TaskQueueSet's for work stealing.
596
597 #undef TRACESPINNING
598
599 class ParallelTaskTerminator: public StackObj {
600 private:
601 int _n_threads;
602 TaskQueueSetSuper* _queue_set;
603 int _offered_termination;
604
605 #ifdef TRACESPINNING
606 static uint _total_yields;
607 static uint _total_spins;
608 static uint _total_peeks;
609 #endif
610
611 bool peek_in_queue_set();
612 protected:
613 virtual void yield();
614 void sleep(uint millis);
615
616 public:
617
618 // "n_threads" is the number of threads to be terminated. "queue_set" is a
619 // queue sets of work queues of other threads.
620 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
621
622 // The current thread has no work, and is ready to terminate if everyone
623 // else is. If returns "true", all threads are terminated. If returns
624 // "false", available work has been observed in one of the task queues,
625 // so the global task is not complete.
626 bool offer_termination() {
627 return offer_termination(NULL);
628 }
629
630 // As above, but it also terminates if the should_exit_termination()
631 // method of the terminator parameter returns true. If terminator is
632 // NULL, then it is ignored.
633 bool offer_termination(TerminatorTerminator* terminator);
634
635 // Reset the terminator, so that it may be reused again.
636 // The caller is responsible for ensuring that this is done
637 // in an MT-safe manner, once the previous round of use of
638 // the terminator is finished.
639 void reset_for_reuse();
640
641 #ifdef TRACESPINNING
642 static uint total_yields() { return _total_yields; }
643 static uint total_spins() { return _total_spins; }
644 static uint total_peeks() { return _total_peeks; }
645 static void print_termination_counts();
646 #endif
647 };
648
649 template<class E, unsigned int N> inline bool
650 GenericTaskQueue<E, N>::push(E t) {
651 uint localBot = _bottom;
652 assert((localBot >= 0) && (localBot < N), "_bottom out of range.");
653 idx_t top = _age.top();
654 uint dirty_n_elems = dirty_size(localBot, top);
655 assert(dirty_n_elems < N, "n_elems out of range.");
656 if (dirty_n_elems < max_elems()) {
657 // g++ complains if the volatile result of the assignment is unused.
658 const_cast<E&>(_elems[localBot] = t);
659 OrderAccess::release_store(&_bottom, increment_index(localBot));
660 TASKQUEUE_STATS_ONLY(stats.record_push());
661 return true;
662 } else {
663 return push_slow(t, dirty_n_elems);
664 }
665 }
666
667 template<class E, unsigned int N> inline bool
668 GenericTaskQueue<E, N>::pop_local(E& t) {
669 uint localBot = _bottom;
670 // This value cannot be N-1. That can only occur as a result of
671 // the assignment to bottom in this method. If it does, this method
672 // resets the size to 0 before the next call (which is sequential,
673 // since this is pop_local.)
674 uint dirty_n_elems = dirty_size(localBot, _age.top());
675 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
676 if (dirty_n_elems == 0) return false;
677 localBot = decrement_index(localBot);
678 _bottom = localBot;
679 // This is necessary to prevent any read below from being reordered
680 // before the store just above.
681 OrderAccess::fence();
682 const_cast<E&>(t = _elems[localBot]);
683 // This is a second read of "age"; the "size()" above is the first.
684 // If there's still at least one element in the queue, based on the
685 // "_bottom" and "age" we've read, then there can be no interference with
686 // a "pop_global" operation, and we're done.
687 idx_t tp = _age.top(); // XXX
688 if (size(localBot, tp) > 0) {
689 assert(dirty_size(localBot, tp) != N - 1, "sanity");
690 TASKQUEUE_STATS_ONLY(stats.record_pop());
691 return true;
692 } else {
693 // Otherwise, the queue contained exactly one element; we take the slow
694 // path.
695 return pop_local_slow(localBot, _age.get());
696 }
697 }
698
699 typedef GenericTaskQueue<oop> OopTaskQueue;
700 typedef GenericTaskQueueSet<OopTaskQueue> OopTaskQueueSet;
701
702 #ifdef _MSC_VER
703 #pragma warning(push)
704 // warning C4522: multiple assignment operators specified
705 #pragma warning(disable:4522)
706 #endif
707
708 // This is a container class for either an oop* or a narrowOop*.
709 // Both are pushed onto a task queue and the consumer will test is_narrow()
710 // to determine which should be processed.
711 class StarTask {
712 void* _holder; // either union oop* or narrowOop*
713
714 enum { COMPRESSED_OOP_MASK = 1 };
715
716 public:
717 StarTask(narrowOop* p) {
718 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
719 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
720 }
721 StarTask(oop* p) {
722 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
723 _holder = (void*)p;
724 }
725 StarTask() { _holder = NULL; }
726 operator oop*() { return (oop*)_holder; }
727 operator narrowOop*() {
728 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
729 }
730
731 StarTask& operator=(const StarTask& t) {
732 _holder = t._holder;
733 return *this;
734 }
735 volatile StarTask& operator=(const volatile StarTask& t) volatile {
736 _holder = t._holder;
737 return *this;
738 }
739
740 bool is_narrow() const {
741 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
742 }
743 };
744
745 class ObjArrayTask
746 {
747 public:
748 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
749 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
750 assert(idx <= size_t(max_jint), "too big");
751 }
752 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
753
754 ObjArrayTask& operator =(const ObjArrayTask& t) {
755 _obj = t._obj;
756 _index = t._index;
757 return *this;
758 }
759 volatile ObjArrayTask&
760 operator =(const volatile ObjArrayTask& t) volatile {
761 _obj = t._obj;
762 _index = t._index;
763 return *this;
764 }
765
766 inline oop obj() const { return _obj; }
767 inline int index() const { return _index; }
768
769 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
770
771 private:
772 oop _obj;
773 int _index;
774 };
775
776 #ifdef _MSC_VER
777 #pragma warning(pop)
778 #endif
779
780 typedef OverflowTaskQueue<StarTask> OopStarTaskQueue;
781 typedef GenericTaskQueueSet<OopStarTaskQueue> OopStarTaskQueueSet;
782
783 typedef OverflowTaskQueue<size_t> RegionTaskQueue;
784 typedef GenericTaskQueueSet<RegionTaskQueue> RegionTaskQueueSet;