1 /*
2 * Copyright (c) 2001, 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 #ifndef SHARE_VM_UTILITIES_TASKQUEUE_HPP
26 #define SHARE_VM_UTILITIES_TASKQUEUE_HPP
27
28 #include "memory/allocation.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "runtime/mutex.hpp"
31 #include "runtime/orderAccess.inline.hpp"
32 #include "utilities/stack.hpp"
33
34 // Simple TaskQueue stats that are collected by default in debug builds.
35
36 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
37 #define TASKQUEUE_STATS 1
38 #elif !defined(TASKQUEUE_STATS)
39 #define TASKQUEUE_STATS 0
40 #endif
41
42 #if TASKQUEUE_STATS
43 #define TASKQUEUE_STATS_ONLY(code) code
44 #else
45 #define TASKQUEUE_STATS_ONLY(code)
46 #endif // TASKQUEUE_STATS
47
48 #if TASKQUEUE_STATS
49 class TaskQueueStats {
50 public:
51 enum StatId {
52 push, // number of taskqueue pushes
53 pop, // number of taskqueue pops
54 pop_slow, // subset of taskqueue pops that were done slow-path
55 steal_attempt, // number of taskqueue steal attempts
56 steal, // number of taskqueue steals
57 overflow, // number of overflow pushes
58 overflow_max_len, // max length of overflow stack
59 last_stat_id
60 };
61
62 public:
63 inline TaskQueueStats() { reset(); }
64
65 inline void record_push() { ++_stats[push]; }
66 inline void record_pop() { ++_stats[pop]; }
67 inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
68 inline void record_steal(bool success);
69 inline void record_overflow(size_t new_length);
70
71 TaskQueueStats & operator +=(const TaskQueueStats & addend);
72
73 inline size_t get(StatId id) const { return _stats[id]; }
74 inline const size_t* get() const { return _stats; }
75
76 inline void reset();
77
78 // Print the specified line of the header (does not include a line separator).
79 static void print_header(unsigned int line, outputStream* const stream = tty,
80 unsigned int width = 10);
81 // Print the statistics (does not include a line separator).
82 void print(outputStream* const stream = tty, unsigned int width = 10) const;
83
84 DEBUG_ONLY(void verify() const;)
85
86 private:
87 size_t _stats[last_stat_id];
88 static const char * const _names[last_stat_id];
89 };
90
91 void TaskQueueStats::record_steal(bool success) {
92 ++_stats[steal_attempt];
93 if (success) ++_stats[steal];
94 }
95
96 void TaskQueueStats::record_overflow(size_t new_len) {
97 ++_stats[overflow];
98 if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
99 }
100
101 void TaskQueueStats::reset() {
102 memset(_stats, 0, sizeof(_stats));
103 }
104 #endif // TASKQUEUE_STATS
105
106 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
107
108 template <unsigned int N, MEMFLAGS F>
109 class TaskQueueSuper: public CHeapObj<F> {
110 protected:
111 // Internal type for indexing the queue; also used for the tag.
112 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
113
114 // The first free element after the last one pushed (mod N).
115 volatile uint _bottom;
116
117 enum { MOD_N_MASK = N - 1 };
118
119 class Age {
120 public:
121 Age(size_t data = 0) { _data = data; }
122 Age(const Age& age) { _data = age._data; }
123 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
124
125 Age get() const volatile { return _data; }
126 void set(Age age) volatile { _data = age._data; }
127
128 idx_t top() const volatile { return _fields._top; }
129 idx_t tag() const volatile { return _fields._tag; }
130
131 // Increment top; if it wraps, increment tag also.
132 void increment() {
133 _fields._top = increment_index(_fields._top);
134 if (_fields._top == 0) ++_fields._tag;
135 }
136
137 Age cmpxchg(const Age new_age, const Age old_age) volatile {
138 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
139 (volatile intptr_t *)&_data,
140 (intptr_t)old_age._data);
141 }
142
143 bool operator ==(const Age& other) const { return _data == other._data; }
144
145 private:
146 struct fields {
147 idx_t _top;
148 idx_t _tag;
149 };
150 union {
151 size_t _data;
152 fields _fields;
153 };
154 };
155
156 volatile Age _age;
157
158 // These both operate mod N.
159 static uint increment_index(uint ind) {
160 return (ind + 1) & MOD_N_MASK;
161 }
162 static uint decrement_index(uint ind) {
163 return (ind - 1) & MOD_N_MASK;
164 }
165
166 // Returns a number in the range [0..N). If the result is "N-1", it should be
167 // interpreted as 0.
168 uint dirty_size(uint bot, uint top) const {
169 return (bot - top) & MOD_N_MASK;
170 }
171
172 // Returns the size corresponding to the given "bot" and "top".
173 uint size(uint bot, uint top) const {
174 uint sz = dirty_size(bot, top);
175 // Has the queue "wrapped", so that bottom is less than top? There's a
176 // complicated special case here. A pair of threads could perform pop_local
177 // and pop_global operations concurrently, starting from a state in which
178 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
179 // and the pop_global in incrementing _top (in which case the pop_global
180 // will be awarded the contested queue element.) The resulting state must
181 // be interpreted as an empty queue. (We only need to worry about one such
182 // event: only the queue owner performs pop_local's, and several concurrent
183 // threads attempting to perform the pop_global will all perform the same
184 // CAS, and only one can succeed.) Any stealing thread that reads after
185 // either the increment or decrement will see an empty queue, and will not
186 // join the competitors. The "sz == -1 || sz == N-1" state will not be
187 // modified by concurrent queues, so the owner thread can reset the state to
188 // _bottom == top so subsequent pushes will be performed normally.
189 return (sz == N - 1) ? 0 : sz;
190 }
191
192 public:
193 TaskQueueSuper() : _bottom(0), _age() {}
194
195 // Return true if the TaskQueue contains/does not contain any tasks.
196 bool peek() const { return _bottom != _age.top(); }
197 bool is_empty() const { return size() == 0; }
198
199 // Return an estimate of the number of elements in the queue.
200 // The "careful" version admits the possibility of pop_local/pop_global
201 // races.
202 uint size() const {
203 return size(_bottom, _age.top());
204 }
205
206 uint dirty_size() const {
207 return dirty_size(_bottom, _age.top());
208 }
209
210 void set_empty() {
211 _bottom = 0;
212 _age.set(0);
213 }
214
215 // Maximum number of elements allowed in the queue. This is two less
216 // than the actual queue size, for somewhat complicated reasons.
217 uint max_elems() const { return N - 2; }
218
219 // Total size of queue.
220 static const uint total_size() { return N; }
221
222 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
223 };
224
225 //
226 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
227 // ended-queue (deque), intended for use in work stealing. Queue operations
228 // are non-blocking.
229 //
230 // A queue owner thread performs push() and pop_local() operations on one end
231 // of the queue, while other threads may steal work using the pop_global()
232 // method.
233 //
234 // The main difference to the original algorithm is that this
235 // implementation allows wrap-around at the end of its allocated
236 // storage, which is an array.
237 //
238 // The original paper is:
239 //
240 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
241 // Thread scheduling for multiprogrammed multiprocessors.
242 // Theory of Computing Systems 34, 2 (2001), 115-144.
243 //
244 // The following paper provides an correctness proof and an
245 // implementation for weakly ordered memory models including (pseudo-)
246 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
247 // similar to ABP, with the main difference that it allows resizing of the
248 // underlying storage:
249 //
250 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
251 // Correct and efficient work-stealing for weak memory models
252 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
253 // practice of parallel programming (PPoPP 2013), 69-80
254 //
255
256 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
257 class GenericTaskQueue: public TaskQueueSuper<N, F> {
258 ArrayAllocator<E, F> _array_allocator;
259 protected:
260 typedef typename TaskQueueSuper<N, F>::Age Age;
261 typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
262
263 using TaskQueueSuper<N, F>::_bottom;
264 using TaskQueueSuper<N, F>::_age;
265 using TaskQueueSuper<N, F>::increment_index;
266 using TaskQueueSuper<N, F>::decrement_index;
267 using TaskQueueSuper<N, F>::dirty_size;
268
269 public:
270 using TaskQueueSuper<N, F>::max_elems;
271 using TaskQueueSuper<N, F>::size;
272
273 #if TASKQUEUE_STATS
274 using TaskQueueSuper<N, F>::stats;
275 #endif
276
277 private:
278 // Slow paths for push, pop_local. (pop_global has no fast path.)
279 bool push_slow(E t, uint dirty_n_elems);
280 bool pop_local_slow(uint localBot, Age oldAge);
281
282 public:
283 typedef E element_type;
284
285 // Initializes the queue to empty.
286 GenericTaskQueue();
287
288 void initialize();
289
290 // Push the task "t" on the queue. Returns "false" iff the queue is full.
291 inline bool push(E t);
292
293 // Attempts to claim a task from the "local" end of the queue (the most
294 // recently pushed). If successful, returns true and sets t to the task;
295 // otherwise, returns false (the queue is empty).
296 inline bool pop_local(volatile E& t);
297
298 // Like pop_local(), but uses the "global" end of the queue (the least
299 // recently pushed).
300 bool pop_global(volatile E& t);
301
302 // Delete any resource associated with the queue.
303 ~GenericTaskQueue();
304
305 // apply the closure to all elements in the task queue
306 void oops_do(OopClosure* f);
307
308 private:
309 // Element array.
310 volatile E* _elems;
311 };
312
313 template<class E, MEMFLAGS F, unsigned int N>
314 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
315 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
316 }
317
318 template<class E, MEMFLAGS F, unsigned int N>
319 void GenericTaskQueue<E, F, N>::initialize() {
320 _elems = _array_allocator.allocate(N);
321 }
322
323 template<class E, MEMFLAGS F, unsigned int N>
324 void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {
325 // tty->print_cr("START OopTaskQueue::oops_do");
326 uint iters = size();
327 uint index = _bottom;
328 for (uint i = 0; i < iters; ++i) {
329 index = decrement_index(index);
330 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
331 // index, &_elems[index], _elems[index]);
332 E* t = (E*)&_elems[index]; // cast away volatility
333 oop* p = (oop*)t;
334 assert((*t)->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(*t)));
335 f->do_oop(p);
336 }
337 // tty->print_cr("END OopTaskQueue::oops_do");
338 }
339
340 // pop_local_slow() is done by the owning thread and is trying to
341 // get the last task in the queue. It will compete with pop_global()
342 // that will be used by other threads. The tag age is incremented
343 // whenever the queue goes empty which it will do here if this thread
344 // gets the last task or in pop_global() if the queue wraps (top == 0
345 // and pop_global() succeeds, see pop_global()).
346 template<class E, MEMFLAGS F, unsigned int N>
347 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
348 // This queue was observed to contain exactly one element; either this
349 // thread will claim it, or a competing "pop_global". In either case,
350 // the queue will be logically empty afterwards. Create a new Age value
351 // that represents the empty queue for the given value of "_bottom". (We
352 // must also increment "tag" because of the case where "bottom == 1",
353 // "top == 0". A pop_global could read the queue element in that case,
354 // then have the owner thread do a pop followed by another push. Without
355 // the incrementing of "tag", the pop_global's CAS could succeed,
356 // allowing it to believe it has claimed the stale element.)
357 Age newAge((idx_t)localBot, oldAge.tag() + 1);
358 // Perhaps a competing pop_global has already incremented "top", in which
359 // case it wins the element.
360 if (localBot == oldAge.top()) {
361 // No competing pop_global has yet incremented "top"; we'll try to
362 // install new_age, thus claiming the element.
363 Age tempAge = _age.cmpxchg(newAge, oldAge);
364 if (tempAge == oldAge) {
365 // We win.
366 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
367 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
368 return true;
369 }
370 }
371 // We lose; a completing pop_global gets the element. But the queue is empty
372 // and top is greater than bottom. Fix this representation of the empty queue
373 // to become the canonical one.
374 _age.set(newAge);
375 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
376 return false;
377 }
378
379 template<class E, MEMFLAGS F, unsigned int N>
380 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
381 Age oldAge = _age.get();
382 // Architectures with weak memory model require a barrier here
383 // to guarantee that bottom is not older than age,
384 // which is crucial for the correctness of the algorithm.
385 #if !(defined SPARC || defined IA32 || defined AMD64)
386 OrderAccess::fence();
387 #endif
388 uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
389 uint n_elems = size(localBot, oldAge.top());
390 if (n_elems == 0) {
391 return false;
392 }
393
394 // g++ complains if the volatile result of the assignment is
395 // unused, so we cast the volatile away. We cannot cast directly
396 // to void, because gcc treats that as not using the result of the
397 // assignment. However, casting to E& means that we trigger an
398 // unused-value warning. So, we cast the E& to void.
399 (void) const_cast<E&>(t = _elems[oldAge.top()]);
400 Age newAge(oldAge);
401 newAge.increment();
402 Age resAge = _age.cmpxchg(newAge, oldAge);
403
404 // Note that using "_bottom" here might fail, since a pop_local might
405 // have decremented it.
406 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
407 return resAge == oldAge;
408 }
409
410 template<class E, MEMFLAGS F, unsigned int N>
411 GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
412 FREE_C_HEAP_ARRAY(E, _elems);
413 }
414
415 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
416 // elements that do not fit in the TaskQueue.
417 //
418 // This class hides two methods from super classes:
419 //
420 // push() - push onto the task queue or, if that fails, onto the overflow stack
421 // is_empty() - return true if both the TaskQueue and overflow stack are empty
422 //
423 // Note that size() is not hidden--it returns the number of elements in the
424 // TaskQueue, and does not include the size of the overflow stack. This
425 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
426 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
427 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
428 {
429 public:
430 typedef Stack<E, F> overflow_t;
431 typedef GenericTaskQueue<E, F, N> taskqueue_t;
432
433 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
434
435 // Push task t onto the queue or onto the overflow stack. Return true.
436 inline bool push(E t);
437
438 // Attempt to pop from the overflow stack; return true if anything was popped.
439 inline bool pop_overflow(E& t);
440
441 inline overflow_t* overflow_stack() { return &_overflow_stack; }
442
443 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
444 inline bool overflow_empty() const { return _overflow_stack.is_empty(); }
445 inline bool is_empty() const {
446 return taskqueue_empty() && overflow_empty();
447 }
448
449 private:
450 overflow_t _overflow_stack;
451 };
452
453 template <class E, MEMFLAGS F, unsigned int N>
454 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
455 {
456 if (overflow_empty()) return false;
457 t = overflow_stack()->pop();
458 return true;
459 }
460
461 class TaskQueueSetSuper {
462 protected:
463 static int randomParkAndMiller(int* seed0);
464 public:
465 // Returns "true" if some TaskQueue in the set contains a task.
466 virtual bool peek() = 0;
467 };
468
469 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
470 };
471
472 template<class T, MEMFLAGS F>
473 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
474 private:
475 uint _n;
476 T** _queues;
477
478 public:
479 typedef typename T::element_type E;
480
481 GenericTaskQueueSet(int n) : _n(n) {
482 typedef T* GenericTaskQueuePtr;
483 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);
484 for (int i = 0; i < n; i++) {
485 _queues[i] = NULL;
486 }
487 }
488
489 bool steal_best_of_2(uint queue_num, int* seed, E& t);
490
491 void register_queue(uint i, T* q);
492
493 T* queue(uint n);
494
495 // The thread with queue number "queue_num" (and whose random number seed is
496 // at "seed") is trying to steal a task from some other queue. (It may try
497 // several queues, according to some configuration parameter.) If some steal
498 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
499 // false.
500 bool steal(uint queue_num, int* seed, E& t);
501
502 bool peek();
503 };
504
505 template<class T, MEMFLAGS F> void
506 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
507 assert(i < _n, "index out of range.");
508 _queues[i] = q;
509 }
510
511 template<class T, MEMFLAGS F> T*
512 GenericTaskQueueSet<T, F>::queue(uint i) {
513 return _queues[i];
514 }
515
516 template<class T, MEMFLAGS F> bool
517 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
518 for (uint i = 0; i < 2 * _n; i++) {
519 if (steal_best_of_2(queue_num, seed, t)) {
520 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
521 return true;
522 }
523 }
524 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
525 return false;
526 }
527
528 template<class T, MEMFLAGS F> bool
529 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
530 if (_n > 2) {
531 uint k1 = queue_num;
532 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
533 uint k2 = queue_num;
534 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
535 // Sample both and try the larger.
536 uint sz1 = _queues[k1]->size();
537 uint sz2 = _queues[k2]->size();
538 if (sz2 > sz1) return _queues[k2]->pop_global(t);
539 else return _queues[k1]->pop_global(t);
540 } else if (_n == 2) {
541 // Just try the other one.
542 uint k = (queue_num + 1) % 2;
543 return _queues[k]->pop_global(t);
544 } else {
545 assert(_n == 1, "can't be zero.");
546 return false;
547 }
548 }
549
550 template<class T, MEMFLAGS F>
551 bool GenericTaskQueueSet<T, F>::peek() {
552 // Try all the queues.
553 for (uint j = 0; j < _n; j++) {
554 if (_queues[j]->peek())
555 return true;
556 }
557 return false;
558 }
559
560 // When to terminate from the termination protocol.
561 class TerminatorTerminator: public CHeapObj<mtInternal> {
562 public:
563 virtual bool should_exit_termination() = 0;
564 };
565
566 // A class to aid in the termination of a set of parallel tasks using
567 // TaskQueueSet's for work stealing.
568
569 #undef TRACESPINNING
570
571 class ParallelTaskTerminator: public StackObj {
572 private:
573 int _n_threads;
574 TaskQueueSetSuper* _queue_set;
575 int _offered_termination;
576
577 #ifdef TRACESPINNING
578 static uint _total_yields;
579 static uint _total_spins;
580 static uint _total_peeks;
581 #endif
582
583 bool peek_in_queue_set();
584 protected:
585 virtual void yield();
586 void sleep(uint millis);
587
588 public:
589
590 // "n_threads" is the number of threads to be terminated. "queue_set" is a
591 // queue sets of work queues of other threads.
592 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
593
594 // The current thread has no work, and is ready to terminate if everyone
595 // else is. If returns "true", all threads are terminated. If returns
596 // "false", available work has been observed in one of the task queues,
597 // so the global task is not complete.
598 bool offer_termination() {
599 return offer_termination(NULL);
600 }
601
602 // As above, but it also terminates if the should_exit_termination()
603 // method of the terminator parameter returns true. If terminator is
604 // NULL, then it is ignored.
605 bool offer_termination(TerminatorTerminator* terminator);
606
607 // Reset the terminator, so that it may be reused again.
608 // The caller is responsible for ensuring that this is done
609 // in an MT-safe manner, once the previous round of use of
610 // the terminator is finished.
611 void reset_for_reuse();
612 // Same as above but the number of parallel threads is set to the
613 // given number.
614 void reset_for_reuse(int n_threads);
615
616 #ifdef TRACESPINNING
617 static uint total_yields() { return _total_yields; }
618 static uint total_spins() { return _total_spins; }
619 static uint total_peeks() { return _total_peeks; }
620 static void print_termination_counts();
621 #endif
622 };
623
624 template<class E, MEMFLAGS F, unsigned int N> inline bool
625 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
626 uint localBot = _bottom;
627 // This value cannot be N-1. That can only occur as a result of
628 // the assignment to bottom in this method. If it does, this method
629 // resets the size to 0 before the next call (which is sequential,
630 // since this is pop_local.)
631 uint dirty_n_elems = dirty_size(localBot, _age.top());
632 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
633 if (dirty_n_elems == 0) return false;
634 localBot = decrement_index(localBot);
635 _bottom = localBot;
636 // This is necessary to prevent any read below from being reordered
637 // before the store just above.
638 OrderAccess::fence();
639 // g++ complains if the volatile result of the assignment is
640 // unused, so we cast the volatile away. We cannot cast directly
641 // to void, because gcc treats that as not using the result of the
642 // assignment. However, casting to E& means that we trigger an
643 // unused-value warning. So, we cast the E& to void.
644 (void) const_cast<E&>(t = _elems[localBot]);
645 // This is a second read of "age"; the "size()" above is the first.
646 // If there's still at least one element in the queue, based on the
647 // "_bottom" and "age" we've read, then there can be no interference with
648 // a "pop_global" operation, and we're done.
649 idx_t tp = _age.top(); // XXX
650 if (size(localBot, tp) > 0) {
651 assert(dirty_size(localBot, tp) != N - 1, "sanity");
652 TASKQUEUE_STATS_ONLY(stats.record_pop());
653 return true;
654 } else {
655 // Otherwise, the queue contained exactly one element; we take the slow
656 // path.
657 return pop_local_slow(localBot, _age.get());
658 }
659 }
660
661 typedef GenericTaskQueue<oop, mtGC> OopTaskQueue;
662 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
663
664 #ifdef _MSC_VER
665 #pragma warning(push)
666 // warning C4522: multiple assignment operators specified
667 #pragma warning(disable:4522)
668 #endif
669
670 // This is a container class for either an oop* or a narrowOop*.
671 // Both are pushed onto a task queue and the consumer will test is_narrow()
672 // to determine which should be processed.
673 class StarTask {
674 void* _holder; // either union oop* or narrowOop*
675
676 enum { COMPRESSED_OOP_MASK = 1 };
677
678 public:
679 StarTask(narrowOop* p) {
680 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
681 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
682 }
683 StarTask(oop* p) {
684 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
685 _holder = (void*)p;
686 }
687 StarTask() { _holder = NULL; }
688 operator oop*() { return (oop*)_holder; }
689 operator narrowOop*() {
690 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
691 }
692
693 StarTask& operator=(const StarTask& t) {
694 _holder = t._holder;
695 return *this;
696 }
697 volatile StarTask& operator=(const volatile StarTask& t) volatile {
698 _holder = t._holder;
699 return *this;
700 }
701
702 bool is_narrow() const {
703 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
704 }
705 };
706
707 class ObjArrayTask
708 {
709 public:
710 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
711 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
712 assert(idx <= size_t(max_jint), "too big");
713 }
714 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
715
716 ObjArrayTask& operator =(const ObjArrayTask& t) {
717 _obj = t._obj;
718 _index = t._index;
719 return *this;
720 }
721 volatile ObjArrayTask&
722 operator =(const volatile ObjArrayTask& t) volatile {
723 (void)const_cast<oop&>(_obj = t._obj);
724 _index = t._index;
725 return *this;
726 }
727
728 inline oop obj() const { return _obj; }
729 inline int index() const { return _index; }
730
731 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
732
733 private:
734 oop _obj;
735 int _index;
736 };
737
738 #ifdef _MSC_VER
739 #pragma warning(pop)
740 #endif
741
742 typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue;
743 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet;
744
745 typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue;
746 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet;
747
748
749 #endif // SHARE_VM_UTILITIES_TASKQUEUE_HPP