1 /*
2 * Copyright (c) 2001, 2012, 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 "utilities/stack.hpp"
32 #ifdef TARGET_OS_ARCH_linux_x86
33 # include "orderAccess_linux_x86.inline.hpp"
34 #endif
35 #ifdef TARGET_OS_ARCH_linux_sparc
36 # include "orderAccess_linux_sparc.inline.hpp"
37 #endif
38 #ifdef TARGET_OS_ARCH_linux_zero
39 # include "orderAccess_linux_zero.inline.hpp"
40 #endif
41 #ifdef TARGET_OS_ARCH_solaris_x86
42 # include "orderAccess_solaris_x86.inline.hpp"
43 #endif
44 #ifdef TARGET_OS_ARCH_solaris_sparc
45 # include "orderAccess_solaris_sparc.inline.hpp"
46 #endif
47 #ifdef TARGET_OS_ARCH_windows_x86
48 # include "orderAccess_windows_x86.inline.hpp"
49 #endif
50 #ifdef TARGET_OS_ARCH_linux_arm
51 # include "orderAccess_linux_arm.inline.hpp"
52 #endif
53 #ifdef TARGET_OS_ARCH_linux_ppc
54 # include "orderAccess_linux_ppc.inline.hpp"
55 #endif
56 #ifdef TARGET_OS_ARCH_bsd_x86
57 # include "orderAccess_bsd_x86.inline.hpp"
58 #endif
59 #ifdef TARGET_OS_ARCH_bsd_zero
60 # include "orderAccess_bsd_zero.inline.hpp"
61 #endif
62
63 // Simple TaskQueue stats that are collected by default in debug builds.
64
65 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
66 #define TASKQUEUE_STATS 1
67 #elif !defined(TASKQUEUE_STATS)
68 #define TASKQUEUE_STATS 0
69 #endif
70
71 #if TASKQUEUE_STATS
72 #define TASKQUEUE_STATS_ONLY(code) code
73 #else
74 #define TASKQUEUE_STATS_ONLY(code)
75 #endif // TASKQUEUE_STATS
76
77 #if TASKQUEUE_STATS
78 class TaskQueueStats {
79 public:
80 enum StatId {
81 push, // number of taskqueue pushes
82 pop, // number of taskqueue pops
83 pop_slow, // subset of taskqueue pops that were done slow-path
84 steal_attempt, // number of taskqueue steal attempts
85 steal, // number of taskqueue steals
86 overflow, // number of overflow pushes
87 overflow_max_len, // max length of overflow stack
88 last_stat_id
89 };
90
91 public:
92 inline TaskQueueStats() { reset(); }
93
94 inline void record_push() { ++_stats[push]; }
95 inline void record_pop() { ++_stats[pop]; }
96 inline void record_pop_slow() { record_pop(); ++_stats[pop_slow]; }
97 inline void record_steal(bool success);
98 inline void record_overflow(size_t new_length);
99
100 TaskQueueStats & operator +=(const TaskQueueStats & addend);
101
102 inline size_t get(StatId id) const { return _stats[id]; }
103 inline const size_t* get() const { return _stats; }
104
105 inline void reset();
106
107 // Print the specified line of the header (does not include a line separator).
108 static void print_header(unsigned int line, outputStream* const stream = tty,
109 unsigned int width = 10);
110 // Print the statistics (does not include a line separator).
111 void print(outputStream* const stream = tty, unsigned int width = 10) const;
112
113 DEBUG_ONLY(void verify() const;)
114
115 private:
116 size_t _stats[last_stat_id];
117 static const char * const _names[last_stat_id];
118 };
119
120 void TaskQueueStats::record_steal(bool success) {
121 ++_stats[steal_attempt];
122 if (success) ++_stats[steal];
123 }
124
125 void TaskQueueStats::record_overflow(size_t new_len) {
126 ++_stats[overflow];
127 if (new_len > _stats[overflow_max_len]) _stats[overflow_max_len] = new_len;
128 }
129
130 void TaskQueueStats::reset() {
131 memset(_stats, 0, sizeof(_stats));
132 }
133 #endif // TASKQUEUE_STATS
134
135 template <unsigned int N, MEMFLAGS F>
136 class TaskQueueSuper: public CHeapObj<F> {
137 protected:
138 // Internal type for indexing the queue; also used for the tag.
139 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
140
141 // The first free element after the last one pushed (mod N).
142 volatile uint _bottom;
143
144 enum { MOD_N_MASK = N - 1 };
145
146 class Age {
147 public:
148 Age(size_t data = 0) { _data = data; }
149 Age(const Age& age) { _data = age._data; }
150 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
151
152 Age get() const volatile { return _data; }
153 void set(Age age) volatile { _data = age._data; }
154
155 idx_t top() const volatile { return _fields._top; }
156 idx_t tag() const volatile { return _fields._tag; }
157
158 // Increment top; if it wraps, increment tag also.
159 void increment() {
160 _fields._top = increment_index(_fields._top);
161 if (_fields._top == 0) ++_fields._tag;
162 }
163
164 Age cmpxchg(const Age new_age, const Age old_age) volatile {
165 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
166 (volatile intptr_t *)&_data,
167 (intptr_t)old_age._data);
168 }
169
170 bool operator ==(const Age& other) const { return _data == other._data; }
171
172 private:
173 struct fields {
174 idx_t _top;
175 idx_t _tag;
176 };
177 union {
178 size_t _data;
179 fields _fields;
180 };
181 };
182
183 volatile Age _age;
184
185 // These both operate mod N.
186 static uint increment_index(uint ind) {
187 return (ind + 1) & MOD_N_MASK;
188 }
189 static uint decrement_index(uint ind) {
190 return (ind - 1) & MOD_N_MASK;
191 }
192
193 // Returns a number in the range [0..N). If the result is "N-1", it should be
194 // interpreted as 0.
195 uint dirty_size(uint bot, uint top) const {
196 return (bot - top) & MOD_N_MASK;
197 }
198
199 // Returns the size corresponding to the given "bot" and "top".
200 uint size(uint bot, uint top) const {
201 uint sz = dirty_size(bot, top);
202 // Has the queue "wrapped", so that bottom is less than top? There's a
203 // complicated special case here. A pair of threads could perform pop_local
204 // and pop_global operations concurrently, starting from a state in which
205 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
206 // and the pop_global in incrementing _top (in which case the pop_global
207 // will be awarded the contested queue element.) The resulting state must
208 // be interpreted as an empty queue. (We only need to worry about one such
209 // event: only the queue owner performs pop_local's, and several concurrent
210 // threads attempting to perform the pop_global will all perform the same
211 // CAS, and only one can succeed.) Any stealing thread that reads after
212 // either the increment or decrement will see an empty queue, and will not
213 // join the competitors. The "sz == -1 || sz == N-1" state will not be
214 // modified by concurrent queues, so the owner thread can reset the state to
215 // _bottom == top so subsequent pushes will be performed normally.
216 return (sz == N - 1) ? 0 : sz;
217 }
218
219 public:
220 TaskQueueSuper() : _bottom(0), _age() {}
221
222 // Return true if the TaskQueue contains/does not contain any tasks.
223 bool peek() const { return _bottom != _age.top(); }
224 bool is_empty() const { return size() == 0; }
225
226 // Return an estimate of the number of elements in the queue.
227 // The "careful" version admits the possibility of pop_local/pop_global
228 // races.
229 uint size() const {
230 return size(_bottom, _age.top());
231 }
232
233 uint dirty_size() const {
234 return dirty_size(_bottom, _age.top());
235 }
236
237 void set_empty() {
238 _bottom = 0;
239 _age.set(0);
240 }
241
242 // Maximum number of elements allowed in the queue. This is two less
243 // than the actual queue size, for somewhat complicated reasons.
244 uint max_elems() const { return N - 2; }
245
246 // Total size of queue.
247 static const uint total_size() { return N; }
248
249 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
250 };
251
252
253
254 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
255 class GenericTaskQueue: public TaskQueueSuper<N, F> {
256 ArrayAllocator<E, F> _array_allocator;
257 protected:
258 typedef typename TaskQueueSuper<N, F>::Age Age;
259 typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
260
261 using TaskQueueSuper<N, F>::_bottom;
262 using TaskQueueSuper<N, F>::_age;
263 using TaskQueueSuper<N, F>::increment_index;
264 using TaskQueueSuper<N, F>::decrement_index;
265 using TaskQueueSuper<N, F>::dirty_size;
266
267 public:
268 using TaskQueueSuper<N, F>::max_elems;
269 using TaskQueueSuper<N, F>::size;
270
271 #if TASKQUEUE_STATS
272 using TaskQueueSuper<N, F>::stats;
273 #endif
274
275 private:
276 // Slow paths for push, pop_local. (pop_global has no fast path.)
277 bool push_slow(E t, uint dirty_n_elems);
278 bool pop_local_slow(uint localBot, Age oldAge);
279
280 public:
281 typedef E element_type;
282
283 // Initializes the queue to empty.
284 GenericTaskQueue();
285
286 void initialize();
287
288 // Push the task "t" on the queue. Returns "false" iff the queue is full.
289 inline bool push(E t);
290
291 // Attempts to claim a task from the "local" end of the queue (the most
292 // recently pushed). If successful, returns true and sets t to the task;
293 // otherwise, returns false (the queue is empty).
294 inline bool pop_local(E& t);
295
296 // Like pop_local(), but uses the "global" end of the queue (the least
297 // recently pushed).
298 bool pop_global(E& t);
299
300 // Delete any resource associated with the queue.
301 ~GenericTaskQueue();
302
303 // apply the closure to all elements in the task queue
304 void oops_do(OopClosure* f);
305
306 private:
307 // Element array.
308 volatile E* _elems;
309 };
310
311 template<class E, MEMFLAGS F, unsigned int N>
312 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
313 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
314 }
315
316 template<class E, MEMFLAGS F, unsigned int N>
317 void GenericTaskQueue<E, F, N>::initialize() {
318 _elems = _array_allocator.allocate(N);
319 }
320
321 template<class E, MEMFLAGS F, unsigned int N>
322 void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {
323 // tty->print_cr("START OopTaskQueue::oops_do");
324 uint iters = size();
325 uint index = _bottom;
326 for (uint i = 0; i < iters; ++i) {
327 index = decrement_index(index);
328 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
329 // index, &_elems[index], _elems[index]);
330 E* t = (E*)&_elems[index]; // cast away volatility
331 oop* p = (oop*)t;
332 assert((*t)->is_oop_or_null(), "Not an oop or null");
333 f->do_oop(p);
334 }
335 // tty->print_cr("END OopTaskQueue::oops_do");
336 }
337
338 template<class E, MEMFLAGS F, unsigned int N>
339 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
340 if (dirty_n_elems == N - 1) {
341 // Actually means 0, so do the push.
342 uint localBot = _bottom;
343 // g++ complains if the volatile result of the assignment is
344 // unused, so we cast the volatile away. We cannot cast directly
345 // to void, because gcc treats that as not using the result of the
346 // assignment. However, casting to E& means that we trigger an
347 // unused-value warning. So, we cast the E& to void.
348 (void)const_cast<E&>(_elems[localBot] = t);
349 OrderAccess::release_store(&_bottom, increment_index(localBot));
350 TASKQUEUE_STATS_ONLY(stats.record_push());
351 return true;
352 }
353 return false;
354 }
355
356 // pop_local_slow() is done by the owning thread and is trying to
357 // get the last task in the queue. It will compete with pop_global()
358 // that will be used by other threads. The tag age is incremented
359 // whenever the queue goes empty which it will do here if this thread
360 // gets the last task or in pop_global() if the queue wraps (top == 0
361 // and pop_global() succeeds, see pop_global()).
362 template<class E, MEMFLAGS F, unsigned int N>
363 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
364 // This queue was observed to contain exactly one element; either this
365 // thread will claim it, or a competing "pop_global". In either case,
366 // the queue will be logically empty afterwards. Create a new Age value
367 // that represents the empty queue for the given value of "_bottom". (We
368 // must also increment "tag" because of the case where "bottom == 1",
369 // "top == 0". A pop_global could read the queue element in that case,
370 // then have the owner thread do a pop followed by another push. Without
371 // the incrementing of "tag", the pop_global's CAS could succeed,
372 // allowing it to believe it has claimed the stale element.)
373 Age newAge((idx_t)localBot, oldAge.tag() + 1);
374 // Perhaps a competing pop_global has already incremented "top", in which
375 // case it wins the element.
376 if (localBot == oldAge.top()) {
377 // No competing pop_global has yet incremented "top"; we'll try to
378 // install new_age, thus claiming the element.
379 Age tempAge = _age.cmpxchg(newAge, oldAge);
380 if (tempAge == oldAge) {
381 // We win.
382 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
383 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
384 return true;
385 }
386 }
387 // We lose; a completing pop_global gets the element. But the queue is empty
388 // and top is greater than bottom. Fix this representation of the empty queue
389 // to become the canonical one.
390 _age.set(newAge);
391 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
392 return false;
393 }
394
395 template<class E, MEMFLAGS F, unsigned int N>
396 bool GenericTaskQueue<E, F, N>::pop_global(E& t) {
397 Age oldAge = _age.get();
398 uint localBot = _bottom;
399 uint n_elems = size(localBot, oldAge.top());
400 if (n_elems == 0) {
401 return false;
402 }
403
404 // g++ complains if the volatile result of the assignment is
405 // unused, so we cast the volatile away. We cannot cast directly
406 // to void, because gcc treats that as not using the result of the
407 // assignment. However, casting to E& means that we trigger an
408 // unused-value warning. So, we cast the E& to void.
409 (void) const_cast<E&>(t = _elems[oldAge.top()]);
410 Age newAge(oldAge);
411 newAge.increment();
412 Age resAge = _age.cmpxchg(newAge, oldAge);
413
414 // Note that using "_bottom" here might fail, since a pop_local might
415 // have decremented it.
416 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
417 return resAge == oldAge;
418 }
419
420 template<class E, MEMFLAGS F, unsigned int N>
421 GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
422 FREE_C_HEAP_ARRAY(E, _elems, F);
423 }
424
425 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
426 // elements that do not fit in the TaskQueue.
427 //
428 // This class hides two methods from super classes:
429 //
430 // push() - push onto the task queue or, if that fails, onto the overflow stack
431 // is_empty() - return true if both the TaskQueue and overflow stack are empty
432 //
433 // Note that size() is not hidden--it returns the number of elements in the
434 // TaskQueue, and does not include the size of the overflow stack. This
435 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
436 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
437 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
438 {
439 public:
440 typedef Stack<E, F> overflow_t;
441 typedef GenericTaskQueue<E, F, N> taskqueue_t;
442
443 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
444
445 // Push task t onto the queue or onto the overflow stack. Return true.
446 inline bool push(E t);
447
448 // Attempt to pop from the overflow stack; return true if anything was popped.
449 inline bool pop_overflow(E& t);
450
451 inline overflow_t* overflow_stack() { return &_overflow_stack; }
452
453 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
454 inline bool overflow_empty() const { return _overflow_stack.is_empty(); }
455 inline bool is_empty() const {
456 return taskqueue_empty() && overflow_empty();
457 }
458
459 private:
460 overflow_t _overflow_stack;
461 };
462
463 template <class E, MEMFLAGS F, unsigned int N>
464 bool OverflowTaskQueue<E, F, N>::push(E t)
465 {
466 if (!taskqueue_t::push(t)) {
467 overflow_stack()->push(t);
468 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
469 }
470 return true;
471 }
472
473 template <class E, MEMFLAGS F, unsigned int N>
474 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
475 {
476 if (overflow_empty()) return false;
477 t = overflow_stack()->pop();
478 return true;
479 }
480
481 class TaskQueueSetSuper {
482 protected:
483 static int randomParkAndMiller(int* seed0);
484 public:
485 // Returns "true" if some TaskQueue in the set contains a task.
486 virtual bool peek() = 0;
487 };
488
489 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
490 };
491
492 template<class T, MEMFLAGS F>
493 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
494 private:
495 uint _n;
496 T** _queues;
497
498 public:
499 typedef typename T::element_type E;
500
501 GenericTaskQueueSet(int n) : _n(n) {
502 typedef T* GenericTaskQueuePtr;
503 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);
504 for (int i = 0; i < n; i++) {
505 _queues[i] = NULL;
506 }
507 }
508
509 bool steal_best_of_2(uint queue_num, int* seed, E& t);
510
511 void register_queue(uint i, T* q);
512
513 T* queue(uint n);
514
515 // The thread with queue number "queue_num" (and whose random number seed is
516 // at "seed") is trying to steal a task from some other queue. (It may try
517 // several queues, according to some configuration parameter.) If some steal
518 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
519 // false.
520 bool steal(uint queue_num, int* seed, E& t);
521
522 bool peek();
523 };
524
525 template<class T, MEMFLAGS F> void
526 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
527 assert(i < _n, "index out of range.");
528 _queues[i] = q;
529 }
530
531 template<class T, MEMFLAGS F> T*
532 GenericTaskQueueSet<T, F>::queue(uint i) {
533 return _queues[i];
534 }
535
536 template<class T, MEMFLAGS F> bool
537 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
538 for (uint i = 0; i < 2 * _n; i++) {
539 if (steal_best_of_2(queue_num, seed, t)) {
540 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
541 return true;
542 }
543 }
544 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
545 return false;
546 }
547
548 template<class T, MEMFLAGS F> bool
549 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
550 if (_n > 2) {
551 uint k1 = queue_num;
552 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
553 uint k2 = queue_num;
554 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
555 // Sample both and try the larger.
556 uint sz1 = _queues[k1]->size();
557 uint sz2 = _queues[k2]->size();
558 if (sz2 > sz1) return _queues[k2]->pop_global(t);
559 else return _queues[k1]->pop_global(t);
560 } else if (_n == 2) {
561 // Just try the other one.
562 uint k = (queue_num + 1) % 2;
563 return _queues[k]->pop_global(t);
564 } else {
565 assert(_n == 1, "can't be zero.");
566 return false;
567 }
568 }
569
570 template<class T, MEMFLAGS F>
571 bool GenericTaskQueueSet<T, F>::peek() {
572 // Try all the queues.
573 for (uint j = 0; j < _n; j++) {
574 if (_queues[j]->peek())
575 return true;
576 }
577 return false;
578 }
579
580 // When to terminate from the termination protocol.
581 class TerminatorTerminator: public CHeapObj<mtInternal> {
582 public:
583 virtual bool should_exit_termination() = 0;
584 };
585
586 // A class to aid in the termination of a set of parallel tasks using
587 // TaskQueueSet's for work stealing.
588
589 #undef TRACESPINNING
590
591 class ParallelTaskTerminator: public StackObj {
592 private:
593 int _n_threads;
594 TaskQueueSetSuper* _queue_set;
595 int _offered_termination;
596
597 #ifdef TRACESPINNING
598 static uint _total_yields;
599 static uint _total_spins;
600 static uint _total_peeks;
601 #endif
602
603 bool peek_in_queue_set();
604 protected:
605 virtual void yield();
606 void sleep(uint millis);
607
608 public:
609
610 // "n_threads" is the number of threads to be terminated. "queue_set" is a
611 // queue sets of work queues of other threads.
612 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
613
614 // The current thread has no work, and is ready to terminate if everyone
615 // else is. If returns "true", all threads are terminated. If returns
616 // "false", available work has been observed in one of the task queues,
617 // so the global task is not complete.
618 bool offer_termination() {
619 return offer_termination(NULL);
620 }
621
622 // As above, but it also terminates if the should_exit_termination()
623 // method of the terminator parameter returns true. If terminator is
624 // NULL, then it is ignored.
625 bool offer_termination(TerminatorTerminator* terminator);
626
627 // Reset the terminator, so that it may be reused again.
628 // The caller is responsible for ensuring that this is done
629 // in an MT-safe manner, once the previous round of use of
630 // the terminator is finished.
631 void reset_for_reuse();
632 // Same as above but the number of parallel threads is set to the
633 // given number.
634 void reset_for_reuse(int n_threads);
635
636 #ifdef TRACESPINNING
637 static uint total_yields() { return _total_yields; }
638 static uint total_spins() { return _total_spins; }
639 static uint total_peeks() { return _total_peeks; }
640 static void print_termination_counts();
641 #endif
642 };
643
644 template<class E, MEMFLAGS F, unsigned int N> inline bool
645 GenericTaskQueue<E, F, N>::push(E t) {
646 uint localBot = _bottom;
647 assert((localBot >= 0) && (localBot < N), "_bottom out of range.");
648 idx_t top = _age.top();
649 uint dirty_n_elems = dirty_size(localBot, top);
650 assert(dirty_n_elems < N, "n_elems out of range.");
651 if (dirty_n_elems < max_elems()) {
652 // g++ complains if the volatile result of the assignment is
653 // unused, so we cast the volatile away. We cannot cast directly
654 // to void, because gcc treats that as not using the result of the
655 // assignment. However, casting to E& means that we trigger an
656 // unused-value warning. So, we cast the E& to void.
657 (void) const_cast<E&>(_elems[localBot] = t);
658 OrderAccess::release_store(&_bottom, increment_index(localBot));
659 TASKQUEUE_STATS_ONLY(stats.record_push());
660 return true;
661 } else {
662 return push_slow(t, dirty_n_elems);
663 }
664 }
665
666 template<class E, MEMFLAGS F, unsigned int N> inline bool
667 GenericTaskQueue<E, F, N>::pop_local(E& t) {
668 uint localBot = _bottom;
669 // This value cannot be N-1. That can only occur as a result of
670 // the assignment to bottom in this method. If it does, this method
671 // resets the size to 0 before the next call (which is sequential,
672 // since this is pop_local.)
673 uint dirty_n_elems = dirty_size(localBot, _age.top());
674 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
675 if (dirty_n_elems == 0) return false;
676 localBot = decrement_index(localBot);
677 _bottom = localBot;
678 // This is necessary to prevent any read below from being reordered
679 // before the store just above.
680 OrderAccess::fence();
681 // g++ complains if the volatile result of the assignment is
682 // unused, so we cast the volatile away. We cannot cast directly
683 // to void, because gcc treats that as not using the result of the
684 // assignment. However, casting to E& means that we trigger an
685 // unused-value warning. So, we cast the E& to void.
686 (void) const_cast<E&>(t = _elems[localBot]);
687 // This is a second read of "age"; the "size()" above is the first.
688 // If there's still at least one element in the queue, based on the
689 // "_bottom" and "age" we've read, then there can be no interference with
690 // a "pop_global" operation, and we're done.
691 idx_t tp = _age.top(); // XXX
692 if (size(localBot, tp) > 0) {
693 assert(dirty_size(localBot, tp) != N - 1, "sanity");
694 TASKQUEUE_STATS_ONLY(stats.record_pop());
695 return true;
696 } else {
697 // Otherwise, the queue contained exactly one element; we take the slow
698 // path.
699 return pop_local_slow(localBot, _age.get());
700 }
701 }
702
703 typedef GenericTaskQueue<oop, mtGC> OopTaskQueue;
704 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
705
706 #ifdef _MSC_VER
707 #pragma warning(push)
708 // warning C4522: multiple assignment operators specified
709 #pragma warning(disable:4522)
710 #endif
711
712 // This is a container class for either an oop* or a narrowOop*.
713 // Both are pushed onto a task queue and the consumer will test is_narrow()
714 // to determine which should be processed.
715 class StarTask {
716 void* _holder; // either union oop* or narrowOop*
717
718 enum { COMPRESSED_OOP_MASK = 1 };
719
720 public:
721 StarTask(narrowOop* p) {
722 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
723 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
724 }
725 StarTask(oop* p) {
726 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
727 _holder = (void*)p;
728 }
729 StarTask() { _holder = NULL; }
730 operator oop*() { return (oop*)_holder; }
731 operator narrowOop*() {
732 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
733 }
734
735 StarTask& operator=(const StarTask& t) {
736 _holder = t._holder;
737 return *this;
738 }
739 volatile StarTask& operator=(const volatile StarTask& t) volatile {
740 _holder = t._holder;
741 return *this;
742 }
743
744 bool is_narrow() const {
745 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
746 }
747 };
748
749 class ObjArrayTask
750 {
751 public:
752 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
753 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
754 assert(idx <= size_t(max_jint), "too big");
755 }
756 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
757
758 ObjArrayTask& operator =(const ObjArrayTask& t) {
759 _obj = t._obj;
760 _index = t._index;
761 return *this;
762 }
763 volatile ObjArrayTask&
764 operator =(const volatile ObjArrayTask& t) volatile {
765 _obj = t._obj;
766 _index = t._index;
767 return *this;
768 }
769
770 inline oop obj() const { return _obj; }
771 inline int index() const { return _index; }
772
773 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
774
775 private:
776 oop _obj;
777 int _index;
778 };
779
780 #ifdef _MSC_VER
781 #pragma warning(pop)
782 #endif
783
784 typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue;
785 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet;
786
787 typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue;
788 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet;
789
790
791 #endif // SHARE_VM_UTILITIES_TASKQUEUE_HPP