Wed, 03 Jul 2019 20:42:37 +0800
Merge
1 /*
2 * Copyright (c) 2001, 2016, 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 */
25 #ifndef SHARE_VM_UTILITIES_TASKQUEUE_HPP
26 #define SHARE_VM_UTILITIES_TASKQUEUE_HPP
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"
34 // Simple TaskQueue stats that are collected by default in debug builds.
36 #if !defined(TASKQUEUE_STATS) && defined(ASSERT)
37 #define TASKQUEUE_STATS 1
38 #elif !defined(TASKQUEUE_STATS)
39 #define TASKQUEUE_STATS 0
40 #endif
42 #if TASKQUEUE_STATS
43 #define TASKQUEUE_STATS_ONLY(code) code
44 #else
45 #define TASKQUEUE_STATS_ONLY(code)
46 #endif // TASKQUEUE_STATS
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 };
62 public:
63 inline TaskQueueStats() { reset(); }
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);
71 TaskQueueStats & operator +=(const TaskQueueStats & addend);
73 inline size_t get(StatId id) const { return _stats[id]; }
74 inline const size_t* get() const { return _stats; }
76 inline void reset();
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;
84 DEBUG_ONLY(void verify() const;)
86 private:
87 size_t _stats[last_stat_id];
88 static const char * const _names[last_stat_id];
89 };
91 void TaskQueueStats::record_steal(bool success) {
92 ++_stats[steal_attempt];
93 if (success) ++_stats[steal];
94 }
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 }
101 void TaskQueueStats::reset() {
102 memset(_stats, 0, sizeof(_stats));
103 }
104 #endif // TASKQUEUE_STATS
106 // TaskQueueSuper collects functionality common to all GenericTaskQueue instances.
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;
114 #ifdef MIPS
115 private:
116 #endif
117 // The first free element after the last one pushed (mod N).
118 volatile uint _bottom;
120 #ifdef MIPS
121 protected:
122 inline uint get_bottom() const {
123 return OrderAccess::load_acquire((volatile juint*)&_bottom);
124 }
126 inline void set_bottom(uint new_bottom) {
127 OrderAccess::release_store(&_bottom, new_bottom);
128 }
129 #endif
131 enum { MOD_N_MASK = N - 1 };
133 class Age {
134 public:
135 Age(size_t data = 0) { _data = data; }
136 Age(const Age& age) { _data = age._data; }
137 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
139 #ifndef MIPS
140 Age get() const volatile { return _data; }
141 void set(Age age) volatile { _data = age._data; }
143 idx_t top() const volatile { return _fields._top; }
144 idx_t tag() const volatile { return _fields._tag; }
145 #else
146 Age get() const volatile {
147 size_t res = OrderAccess::load_ptr_acquire((volatile intptr_t*) &_data);
148 return *(Age*)(&res);
149 }
150 void set(Age age) volatile { OrderAccess::release_store_ptr((volatile intptr_t*) &_data, *(size_t*)(&age._data)); }
152 idx_t top() const volatile { return OrderAccess::load_acquire((volatile idx_t*) &(_fields._top)); }
153 idx_t tag() const volatile { return OrderAccess::load_acquire((volatile idx_t*) &(_fields._tag)); }
154 #endif
156 // Increment top; if it wraps, increment tag also.
157 void increment() {
158 _fields._top = increment_index(_fields._top);
159 if (_fields._top == 0) ++_fields._tag;
160 }
162 Age cmpxchg(const Age new_age, const Age old_age) volatile {
163 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
164 (volatile intptr_t *)&_data,
165 (intptr_t)old_age._data);
166 }
168 bool operator ==(const Age& other) const { return _data == other._data; }
170 private:
171 struct fields {
172 idx_t _top;
173 idx_t _tag;
174 };
175 union {
176 size_t _data;
177 fields _fields;
178 };
179 };
181 volatile Age _age;
183 // These both operate mod N.
184 static uint increment_index(uint ind) {
185 return (ind + 1) & MOD_N_MASK;
186 }
187 static uint decrement_index(uint ind) {
188 return (ind - 1) & MOD_N_MASK;
189 }
191 // Returns a number in the range [0..N). If the result is "N-1", it should be
192 // interpreted as 0.
193 uint dirty_size(uint bot, uint top) const {
194 return (bot - top) & MOD_N_MASK;
195 }
197 // Returns the size corresponding to the given "bot" and "top".
198 uint size(uint bot, uint top) const {
199 uint sz = dirty_size(bot, top);
200 // Has the queue "wrapped", so that bottom is less than top? There's a
201 // complicated special case here. A pair of threads could perform pop_local
202 // and pop_global operations concurrently, starting from a state in which
203 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
204 // and the pop_global in incrementing _top (in which case the pop_global
205 // will be awarded the contested queue element.) The resulting state must
206 // be interpreted as an empty queue. (We only need to worry about one such
207 // event: only the queue owner performs pop_local's, and several concurrent
208 // threads attempting to perform the pop_global will all perform the same
209 // CAS, and only one can succeed.) Any stealing thread that reads after
210 // either the increment or decrement will see an empty queue, and will not
211 // join the competitors. The "sz == -1 || sz == N-1" state will not be
212 // modified by concurrent queues, so the owner thread can reset the state to
213 // _bottom == top so subsequent pushes will be performed normally.
214 return (sz == N - 1) ? 0 : sz;
215 }
217 public:
218 TaskQueueSuper() : _bottom(0), _age() {}
220 // Return true if the TaskQueue contains/does not contain any tasks.
221 bool peek() const {
222 #ifdef MIPS
223 return get_bottom() != _age.top();
224 #else
225 return _bottom != _age.top();
226 #endif
227 }
228 bool is_empty() const { return size() == 0; }
230 // Return an estimate of the number of elements in the queue.
231 // The "careful" version admits the possibility of pop_local/pop_global
232 // races.
233 uint size() const {
234 #ifdef MIPS
235 return size(get_bottom(), _age.top());
236 #else
237 return size(_bottom, _age.top());
238 #endif
239 }
241 uint dirty_size() const {
242 #ifdef MIPS
243 return dirty_size(get_bottom(), _age.top());
244 #else
245 return dirty_size(_bottom, _age.top());
246 #endif
247 }
249 void set_empty() {
250 #ifdef MIPS
251 set_bottom(0);
252 #else
253 _bottom = 0;
254 #endif
255 _age.set(0);
256 }
258 // Maximum number of elements allowed in the queue. This is two less
259 // than the actual queue size, for somewhat complicated reasons.
260 uint max_elems() const { return N - 2; }
262 // Total size of queue.
263 static const uint total_size() { return N; }
265 TASKQUEUE_STATS_ONLY(TaskQueueStats stats;)
266 };
268 //
269 // GenericTaskQueue implements an ABP, Aurora-Blumofe-Plaxton, double-
270 // ended-queue (deque), intended for use in work stealing. Queue operations
271 // are non-blocking.
272 //
273 // A queue owner thread performs push() and pop_local() operations on one end
274 // of the queue, while other threads may steal work using the pop_global()
275 // method.
276 //
277 // The main difference to the original algorithm is that this
278 // implementation allows wrap-around at the end of its allocated
279 // storage, which is an array.
280 //
281 // The original paper is:
282 //
283 // Arora, N. S., Blumofe, R. D., and Plaxton, C. G.
284 // Thread scheduling for multiprogrammed multiprocessors.
285 // Theory of Computing Systems 34, 2 (2001), 115-144.
286 //
287 // The following paper provides an correctness proof and an
288 // implementation for weakly ordered memory models including (pseudo-)
289 // code containing memory barriers for a Chase-Lev deque. Chase-Lev is
290 // similar to ABP, with the main difference that it allows resizing of the
291 // underlying storage:
292 //
293 // Le, N. M., Pop, A., Cohen A., and Nardell, F. Z.
294 // Correct and efficient work-stealing for weak memory models
295 // Proceedings of the 18th ACM SIGPLAN symposium on Principles and
296 // practice of parallel programming (PPoPP 2013), 69-80
297 //
299 template <class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
300 class GenericTaskQueue: public TaskQueueSuper<N, F> {
301 ArrayAllocator<E, F> _array_allocator;
302 protected:
303 typedef typename TaskQueueSuper<N, F>::Age Age;
304 typedef typename TaskQueueSuper<N, F>::idx_t idx_t;
306 #ifndef MIPS
307 using TaskQueueSuper<N, F>::_bottom;
308 #endif
309 using TaskQueueSuper<N, F>::_age;
310 using TaskQueueSuper<N, F>::increment_index;
311 using TaskQueueSuper<N, F>::decrement_index;
312 using TaskQueueSuper<N, F>::dirty_size;
314 public:
315 using TaskQueueSuper<N, F>::max_elems;
316 using TaskQueueSuper<N, F>::size;
318 #if TASKQUEUE_STATS
319 using TaskQueueSuper<N, F>::stats;
320 #endif
322 private:
323 // Slow paths for push, pop_local. (pop_global has no fast path.)
324 bool push_slow(E t, uint dirty_n_elems);
325 bool pop_local_slow(uint localBot, Age oldAge);
327 public:
328 typedef E element_type;
330 // Initializes the queue to empty.
331 GenericTaskQueue();
333 void initialize();
335 // Push the task "t" on the queue. Returns "false" iff the queue is full.
336 inline bool push(E t);
338 // Attempts to claim a task from the "local" end of the queue (the most
339 // recently pushed). If successful, returns true and sets t to the task;
340 // otherwise, returns false (the queue is empty).
341 inline bool pop_local(volatile E& t);
343 // Like pop_local(), but uses the "global" end of the queue (the least
344 // recently pushed).
345 bool pop_global(volatile E& t);
347 // Delete any resource associated with the queue.
348 ~GenericTaskQueue();
350 // apply the closure to all elements in the task queue
351 void oops_do(OopClosure* f);
353 private:
354 // Element array.
355 volatile E* _elems;
356 };
358 template<class E, MEMFLAGS F, unsigned int N>
359 GenericTaskQueue<E, F, N>::GenericTaskQueue() {
360 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
361 }
363 template<class E, MEMFLAGS F, unsigned int N>
364 void GenericTaskQueue<E, F, N>::initialize() {
365 _elems = _array_allocator.allocate(N);
366 }
368 template<class E, MEMFLAGS F, unsigned int N>
369 void GenericTaskQueue<E, F, N>::oops_do(OopClosure* f) {
370 // tty->print_cr("START OopTaskQueue::oops_do");
371 uint iters = size();
372 #ifdef MIPS
373 uint index = this->get_bottom();
374 #else
375 uint index = _bottom;
376 #endif
377 for (uint i = 0; i < iters; ++i) {
378 index = decrement_index(index);
379 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
380 // index, &_elems[index], _elems[index]);
381 E* t = (E*)&_elems[index]; // cast away volatility
382 oop* p = (oop*)t;
383 assert((*t)->is_oop_or_null(), "Not an oop or null");
384 f->do_oop(p);
385 }
386 // tty->print_cr("END OopTaskQueue::oops_do");
387 }
389 template<class E, MEMFLAGS F, unsigned int N>
390 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
391 if (dirty_n_elems == N - 1) {
392 // Actually means 0, so do the push.
393 #ifdef MIPS
394 uint localBot = this->get_bottom();
395 #else
396 uint localBot = _bottom;
397 #endif
398 // g++ complains if the volatile result of the assignment is
399 // unused, so we cast the volatile away. We cannot cast directly
400 // to void, because gcc treats that as not using the result of the
401 // assignment. However, casting to E& means that we trigger an
402 // unused-value warning. So, we cast the E& to void.
403 (void)const_cast<E&>(_elems[localBot] = t);
404 #ifdef MIPS
405 this->set_bottom(increment_index(localBot));
406 #else
407 OrderAccess::release_store(&_bottom, increment_index(localBot));
408 #endif
409 TASKQUEUE_STATS_ONLY(stats.record_push());
410 return true;
411 }
412 return false;
413 }
415 // pop_local_slow() is done by the owning thread and is trying to
416 // get the last task in the queue. It will compete with pop_global()
417 // that will be used by other threads. The tag age is incremented
418 // whenever the queue goes empty which it will do here if this thread
419 // gets the last task or in pop_global() if the queue wraps (top == 0
420 // and pop_global() succeeds, see pop_global()).
421 template<class E, MEMFLAGS F, unsigned int N>
422 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
423 // This queue was observed to contain exactly one element; either this
424 // thread will claim it, or a competing "pop_global". In either case,
425 // the queue will be logically empty afterwards. Create a new Age value
426 // that represents the empty queue for the given value of "_bottom". (We
427 // must also increment "tag" because of the case where "bottom == 1",
428 // "top == 0". A pop_global could read the queue element in that case,
429 // then have the owner thread do a pop followed by another push. Without
430 // the incrementing of "tag", the pop_global's CAS could succeed,
431 // allowing it to believe it has claimed the stale element.)
432 Age newAge((idx_t)localBot, oldAge.tag() + 1);
433 // Perhaps a competing pop_global has already incremented "top", in which
434 // case it wins the element.
435 if (localBot == oldAge.top()) {
436 // No competing pop_global has yet incremented "top"; we'll try to
437 // install new_age, thus claiming the element.
438 Age tempAge = _age.cmpxchg(newAge, oldAge);
439 if (tempAge == oldAge) {
440 // We win.
441 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
442 TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
443 return true;
444 }
445 }
446 // We lose; a completing pop_global gets the element. But the queue is empty
447 // and top is greater than bottom. Fix this representation of the empty queue
448 // to become the canonical one.
449 _age.set(newAge);
450 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
451 return false;
452 }
454 template<class E, MEMFLAGS F, unsigned int N>
455 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
456 Age oldAge = _age.get();
457 // Architectures with weak memory model require a barrier here
458 // to guarantee that bottom is not older than age,
459 // which is crucial for the correctness of the algorithm.
460 #if !(defined SPARC || defined IA32 || defined AMD64)
461 OrderAccess::fence();
462 #endif
463 #ifdef MIPS
464 uint localBot = this->get_bottom();
465 #else
466 uint localBot = OrderAccess::load_acquire((volatile juint*)&_bottom);
467 #endif
468 uint n_elems = size(localBot, oldAge.top());
469 if (n_elems == 0) {
470 return false;
471 }
473 // g++ complains if the volatile result of the assignment is
474 // unused, so we cast the volatile away. We cannot cast directly
475 // to void, because gcc treats that as not using the result of the
476 // assignment. However, casting to E& means that we trigger an
477 // unused-value warning. So, we cast the E& to void.
478 (void) const_cast<E&>(t = _elems[oldAge.top()]);
479 Age newAge(oldAge);
480 newAge.increment();
481 Age resAge = _age.cmpxchg(newAge, oldAge);
483 // Note that using "_bottom" here might fail, since a pop_local might
484 // have decremented it.
485 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
486 return resAge == oldAge;
487 }
489 template<class E, MEMFLAGS F, unsigned int N>
490 GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
491 FREE_C_HEAP_ARRAY(E, _elems, F);
492 }
494 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
495 // elements that do not fit in the TaskQueue.
496 //
497 // This class hides two methods from super classes:
498 //
499 // push() - push onto the task queue or, if that fails, onto the overflow stack
500 // is_empty() - return true if both the TaskQueue and overflow stack are empty
501 //
502 // Note that size() is not hidden--it returns the number of elements in the
503 // TaskQueue, and does not include the size of the overflow stack. This
504 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
505 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
506 class OverflowTaskQueue: public GenericTaskQueue<E, F, N>
507 {
508 public:
509 typedef Stack<E, F> overflow_t;
510 typedef GenericTaskQueue<E, F, N> taskqueue_t;
512 TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
514 // Push task t onto the queue or onto the overflow stack. Return true.
515 inline bool push(E t);
517 // Try to push task t onto the queue only. Returns true if successful, false otherwise.
518 inline bool try_push_to_taskqueue(E t);
520 // Attempt to pop from the overflow stack; return true if anything was popped.
521 inline bool pop_overflow(E& t);
523 inline overflow_t* overflow_stack() { return &_overflow_stack; }
525 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
526 inline bool overflow_empty() const { return _overflow_stack.is_empty(); }
527 inline bool is_empty() const {
528 return taskqueue_empty() && overflow_empty();
529 }
531 private:
532 overflow_t _overflow_stack;
533 };
535 template <class E, MEMFLAGS F, unsigned int N>
536 bool OverflowTaskQueue<E, F, N>::push(E t)
537 {
538 if (!taskqueue_t::push(t)) {
539 overflow_stack()->push(t);
540 TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
541 }
542 return true;
543 }
545 template <class E, MEMFLAGS F, unsigned int N>
546 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
547 {
548 if (overflow_empty()) return false;
549 t = overflow_stack()->pop();
550 return true;
551 }
553 template <class E, MEMFLAGS F, unsigned int N>
554 bool OverflowTaskQueue<E, F, N>::try_push_to_taskqueue(E t) {
555 return taskqueue_t::push(t);
556 }
557 class TaskQueueSetSuper {
558 protected:
559 static int randomParkAndMiller(int* seed0);
560 public:
561 // Returns "true" if some TaskQueue in the set contains a task.
562 virtual bool peek() = 0;
563 };
565 template <MEMFLAGS F> class TaskQueueSetSuperImpl: public CHeapObj<F>, public TaskQueueSetSuper {
566 };
568 template<class T, MEMFLAGS F>
569 class GenericTaskQueueSet: public TaskQueueSetSuperImpl<F> {
570 private:
571 uint _n;
572 T** _queues;
574 public:
575 typedef typename T::element_type E;
577 GenericTaskQueueSet(int n) : _n(n) {
578 typedef T* GenericTaskQueuePtr;
579 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);
580 for (int i = 0; i < n; i++) {
581 _queues[i] = NULL;
582 }
583 }
585 bool steal_best_of_2(uint queue_num, int* seed, E& t);
587 void register_queue(uint i, T* q);
589 T* queue(uint n);
591 // The thread with queue number "queue_num" (and whose random number seed is
592 // at "seed") is trying to steal a task from some other queue. (It may try
593 // several queues, according to some configuration parameter.) If some steal
594 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
595 // false.
596 bool steal(uint queue_num, int* seed, E& t);
598 bool peek();
599 };
601 template<class T, MEMFLAGS F> void
602 GenericTaskQueueSet<T, F>::register_queue(uint i, T* q) {
603 assert(i < _n, "index out of range.");
604 _queues[i] = q;
605 }
607 template<class T, MEMFLAGS F> T*
608 GenericTaskQueueSet<T, F>::queue(uint i) {
609 return _queues[i];
610 }
612 template<class T, MEMFLAGS F> bool
613 GenericTaskQueueSet<T, F>::steal(uint queue_num, int* seed, E& t) {
614 for (uint i = 0; i < 2 * _n; i++) {
615 if (steal_best_of_2(queue_num, seed, t)) {
616 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(true));
617 return true;
618 }
619 }
620 TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal(false));
621 return false;
622 }
624 template<class T, MEMFLAGS F> bool
625 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, int* seed, E& t) {
626 if (_n > 2) {
627 uint k1 = queue_num;
628 while (k1 == queue_num) k1 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
629 uint k2 = queue_num;
630 while (k2 == queue_num || k2 == k1) k2 = TaskQueueSetSuper::randomParkAndMiller(seed) % _n;
631 // Sample both and try the larger.
632 uint sz1 = _queues[k1]->size();
633 uint sz2 = _queues[k2]->size();
634 if (sz2 > sz1) return _queues[k2]->pop_global(t);
635 else return _queues[k1]->pop_global(t);
636 } else if (_n == 2) {
637 // Just try the other one.
638 uint k = (queue_num + 1) % 2;
639 return _queues[k]->pop_global(t);
640 } else {
641 assert(_n == 1, "can't be zero.");
642 return false;
643 }
644 }
646 template<class T, MEMFLAGS F>
647 bool GenericTaskQueueSet<T, F>::peek() {
648 // Try all the queues.
649 for (uint j = 0; j < _n; j++) {
650 if (_queues[j]->peek())
651 return true;
652 }
653 return false;
654 }
656 // When to terminate from the termination protocol.
657 class TerminatorTerminator: public CHeapObj<mtInternal> {
658 public:
659 virtual bool should_exit_termination() = 0;
660 };
662 // A class to aid in the termination of a set of parallel tasks using
663 // TaskQueueSet's for work stealing.
665 #undef TRACESPINNING
667 class ParallelTaskTerminator: public StackObj {
668 private:
669 int _n_threads;
670 TaskQueueSetSuper* _queue_set;
671 int _offered_termination;
673 #ifdef TRACESPINNING
674 static uint _total_yields;
675 static uint _total_spins;
676 static uint _total_peeks;
677 #endif
679 bool peek_in_queue_set();
680 protected:
681 virtual void yield();
682 void sleep(uint millis);
684 public:
686 // "n_threads" is the number of threads to be terminated. "queue_set" is a
687 // queue sets of work queues of other threads.
688 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
690 // The current thread has no work, and is ready to terminate if everyone
691 // else is. If returns "true", all threads are terminated. If returns
692 // "false", available work has been observed in one of the task queues,
693 // so the global task is not complete.
694 bool offer_termination() {
695 return offer_termination(NULL);
696 }
698 // As above, but it also terminates if the should_exit_termination()
699 // method of the terminator parameter returns true. If terminator is
700 // NULL, then it is ignored.
701 bool offer_termination(TerminatorTerminator* terminator);
703 // Reset the terminator, so that it may be reused again.
704 // The caller is responsible for ensuring that this is done
705 // in an MT-safe manner, once the previous round of use of
706 // the terminator is finished.
707 void reset_for_reuse();
708 // Same as above but the number of parallel threads is set to the
709 // given number.
710 void reset_for_reuse(int n_threads);
712 #ifdef TRACESPINNING
713 static uint total_yields() { return _total_yields; }
714 static uint total_spins() { return _total_spins; }
715 static uint total_peeks() { return _total_peeks; }
716 static void print_termination_counts();
717 #endif
718 };
720 template<class E, MEMFLAGS F, unsigned int N> inline bool
721 GenericTaskQueue<E, F, N>::push(E t) {
722 #ifdef MIPS
723 uint localBot = this->get_bottom();
724 #else
725 uint localBot = _bottom;
726 #endif
727 assert(localBot < N, "_bottom out of range.");
728 idx_t top = _age.top();
729 uint dirty_n_elems = dirty_size(localBot, top);
730 assert(dirty_n_elems < N, "n_elems out of range.");
731 if (dirty_n_elems < max_elems()) {
732 // g++ complains if the volatile result of the assignment is
733 // unused, so we cast the volatile away. We cannot cast directly
734 // to void, because gcc treats that as not using the result of the
735 // assignment. However, casting to E& means that we trigger an
736 // unused-value warning. So, we cast the E& to void.
737 (void) const_cast<E&>(_elems[localBot] = t);
738 #ifdef MIPS
739 this->set_bottom(increment_index(localBot));
740 #else
741 OrderAccess::release_store(&_bottom, increment_index(localBot));
742 #endif
743 TASKQUEUE_STATS_ONLY(stats.record_push());
744 return true;
745 } else {
746 return push_slow(t, dirty_n_elems);
747 }
748 }
750 template<class E, MEMFLAGS F, unsigned int N> inline bool
751 GenericTaskQueue<E, F, N>::pop_local(volatile E& t) {
752 #ifdef MIPS
753 uint localBot = this->get_bottom();
754 #else
755 uint localBot = _bottom;
756 #endif
757 // This value cannot be N-1. That can only occur as a result of
758 // the assignment to bottom in this method. If it does, this method
759 // resets the size to 0 before the next call (which is sequential,
760 // since this is pop_local.)
761 uint dirty_n_elems = dirty_size(localBot, _age.top());
762 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
763 if (dirty_n_elems == 0) return false;
764 localBot = decrement_index(localBot);
765 #ifdef MIPS
766 this->set_bottom(localBot);
767 #else
768 _bottom = localBot;
769 #endif
770 // This is necessary to prevent any read below from being reordered
771 // before the store just above.
772 OrderAccess::fence();
773 // g++ complains if the volatile result of the assignment is
774 // unused, so we cast the volatile away. We cannot cast directly
775 // to void, because gcc treats that as not using the result of the
776 // assignment. However, casting to E& means that we trigger an
777 // unused-value warning. So, we cast the E& to void.
778 (void) const_cast<E&>(t = _elems[localBot]);
779 // This is a second read of "age"; the "size()" above is the first.
780 // If there's still at least one element in the queue, based on the
781 // "_bottom" and "age" we've read, then there can be no interference with
782 // a "pop_global" operation, and we're done.
783 idx_t tp = _age.top(); // XXX
784 if (size(localBot, tp) > 0) {
785 assert(dirty_size(localBot, tp) != N - 1, "sanity");
786 TASKQUEUE_STATS_ONLY(stats.record_pop());
787 return true;
788 } else {
789 // Otherwise, the queue contained exactly one element; we take the slow
790 // path.
791 return pop_local_slow(localBot, _age.get());
792 }
793 }
795 typedef GenericTaskQueue<oop, mtGC> OopTaskQueue;
796 typedef GenericTaskQueueSet<OopTaskQueue, mtGC> OopTaskQueueSet;
798 #ifdef _MSC_VER
799 #pragma warning(push)
800 // warning C4522: multiple assignment operators specified
801 #pragma warning(disable:4522)
802 #endif
804 // This is a container class for either an oop* or a narrowOop*.
805 // Both are pushed onto a task queue and the consumer will test is_narrow()
806 // to determine which should be processed.
807 class StarTask {
808 void* _holder; // either union oop* or narrowOop*
810 enum { COMPRESSED_OOP_MASK = 1 };
812 public:
813 StarTask(narrowOop* p) {
814 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
815 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
816 }
817 StarTask(oop* p) {
818 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
819 _holder = (void*)p;
820 }
821 StarTask() { _holder = NULL; }
822 operator oop*() { return (oop*)_holder; }
823 operator narrowOop*() {
824 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
825 }
827 StarTask& operator=(const StarTask& t) {
828 _holder = t._holder;
829 return *this;
830 }
831 volatile StarTask& operator=(const volatile StarTask& t) volatile {
832 _holder = t._holder;
833 return *this;
834 }
836 bool is_narrow() const {
837 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
838 }
839 };
841 class ObjArrayTask
842 {
843 public:
844 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
845 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
846 assert(idx <= size_t(max_jint), "too big");
847 }
848 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
850 ObjArrayTask& operator =(const ObjArrayTask& t) {
851 _obj = t._obj;
852 _index = t._index;
853 return *this;
854 }
855 volatile ObjArrayTask&
856 operator =(const volatile ObjArrayTask& t) volatile {
857 (void)const_cast<oop&>(_obj = t._obj);
858 _index = t._index;
859 return *this;
860 }
862 inline oop obj() const { return _obj; }
863 inline int index() const { return _index; }
865 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
867 private:
868 oop _obj;
869 int _index;
870 };
872 #ifdef _MSC_VER
873 #pragma warning(pop)
874 #endif
876 typedef OverflowTaskQueue<StarTask, mtClass> OopStarTaskQueue;
877 typedef GenericTaskQueueSet<OopStarTaskQueue, mtClass> OopStarTaskQueueSet;
879 typedef OverflowTaskQueue<size_t, mtInternal> RegionTaskQueue;
880 typedef GenericTaskQueueSet<RegionTaskQueue, mtClass> RegionTaskQueueSet;
883 #endif // SHARE_VM_UTILITIES_TASKQUEUE_HPP