Thu, 01 Jul 2010 21:40:45 -0700
6957084: simplify TaskQueue overflow handling
Reviewed-by: ysr, jmasa
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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13 * accompanied this code).
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23 */
25 template <unsigned int N>
26 class TaskQueueSuper: public CHeapObj {
27 protected:
28 // Internal type for indexing the queue; also used for the tag.
29 typedef NOT_LP64(uint16_t) LP64_ONLY(uint32_t) idx_t;
31 // The first free element after the last one pushed (mod N).
32 volatile uint _bottom;
34 enum { MOD_N_MASK = N - 1 };
36 class Age {
37 public:
38 Age(size_t data = 0) { _data = data; }
39 Age(const Age& age) { _data = age._data; }
40 Age(idx_t top, idx_t tag) { _fields._top = top; _fields._tag = tag; }
42 Age get() const volatile { return _data; }
43 void set(Age age) volatile { _data = age._data; }
45 idx_t top() const volatile { return _fields._top; }
46 idx_t tag() const volatile { return _fields._tag; }
48 // Increment top; if it wraps, increment tag also.
49 void increment() {
50 _fields._top = increment_index(_fields._top);
51 if (_fields._top == 0) ++_fields._tag;
52 }
54 Age cmpxchg(const Age new_age, const Age old_age) volatile {
55 return (size_t) Atomic::cmpxchg_ptr((intptr_t)new_age._data,
56 (volatile intptr_t *)&_data,
57 (intptr_t)old_age._data);
58 }
60 bool operator ==(const Age& other) const { return _data == other._data; }
62 private:
63 struct fields {
64 idx_t _top;
65 idx_t _tag;
66 };
67 union {
68 size_t _data;
69 fields _fields;
70 };
71 };
73 volatile Age _age;
75 // These both operate mod N.
76 static uint increment_index(uint ind) {
77 return (ind + 1) & MOD_N_MASK;
78 }
79 static uint decrement_index(uint ind) {
80 return (ind - 1) & MOD_N_MASK;
81 }
83 // Returns a number in the range [0..N). If the result is "N-1", it should be
84 // interpreted as 0.
85 uint dirty_size(uint bot, uint top) const {
86 return (bot - top) & MOD_N_MASK;
87 }
89 // Returns the size corresponding to the given "bot" and "top".
90 uint size(uint bot, uint top) const {
91 uint sz = dirty_size(bot, top);
92 // Has the queue "wrapped", so that bottom is less than top? There's a
93 // complicated special case here. A pair of threads could perform pop_local
94 // and pop_global operations concurrently, starting from a state in which
95 // _bottom == _top+1. The pop_local could succeed in decrementing _bottom,
96 // and the pop_global in incrementing _top (in which case the pop_global
97 // will be awarded the contested queue element.) The resulting state must
98 // be interpreted as an empty queue. (We only need to worry about one such
99 // event: only the queue owner performs pop_local's, and several concurrent
100 // threads attempting to perform the pop_global will all perform the same
101 // CAS, and only one can succeed.) Any stealing thread that reads after
102 // either the increment or decrement will see an empty queue, and will not
103 // join the competitors. The "sz == -1 || sz == N-1" state will not be
104 // modified by concurrent queues, so the owner thread can reset the state to
105 // _bottom == top so subsequent pushes will be performed normally.
106 return (sz == N - 1) ? 0 : sz;
107 }
109 public:
110 TaskQueueSuper() : _bottom(0), _age() {}
112 // Return true if the TaskQueue contains/does not contain any tasks.
113 bool peek() const { return _bottom != _age.top(); }
114 bool is_empty() const { return size() == 0; }
116 // Return an estimate of the number of elements in the queue.
117 // The "careful" version admits the possibility of pop_local/pop_global
118 // races.
119 uint size() const {
120 return size(_bottom, _age.top());
121 }
123 uint dirty_size() const {
124 return dirty_size(_bottom, _age.top());
125 }
127 void set_empty() {
128 _bottom = 0;
129 _age.set(0);
130 }
132 // Maximum number of elements allowed in the queue. This is two less
133 // than the actual queue size, for somewhat complicated reasons.
134 uint max_elems() const { return N - 2; }
136 // Total size of queue.
137 static const uint total_size() { return N; }
138 };
140 template<class E, unsigned int N = TASKQUEUE_SIZE>
141 class GenericTaskQueue: public TaskQueueSuper<N> {
142 protected:
143 typedef typename TaskQueueSuper<N>::Age Age;
144 typedef typename TaskQueueSuper<N>::idx_t idx_t;
146 using TaskQueueSuper<N>::_bottom;
147 using TaskQueueSuper<N>::_age;
148 using TaskQueueSuper<N>::increment_index;
149 using TaskQueueSuper<N>::decrement_index;
150 using TaskQueueSuper<N>::dirty_size;
152 public:
153 using TaskQueueSuper<N>::max_elems;
154 using TaskQueueSuper<N>::size;
156 private:
157 // Slow paths for push, pop_local. (pop_global has no fast path.)
158 bool push_slow(E t, uint dirty_n_elems);
159 bool pop_local_slow(uint localBot, Age oldAge);
161 public:
162 typedef E element_type;
164 // Initializes the queue to empty.
165 GenericTaskQueue();
167 void initialize();
169 // Push the task "t" on the queue. Returns "false" iff the queue is full.
170 inline bool push(E t);
172 // Attempts to claim a task from the "local" end of the queue (the most
173 // recently pushed). If successful, returns true and sets t to the task;
174 // otherwise, returns false (the queue is empty).
175 inline bool pop_local(E& t);
177 // Like pop_local(), but uses the "global" end of the queue (the least
178 // recently pushed).
179 bool pop_global(E& t);
181 // Delete any resource associated with the queue.
182 ~GenericTaskQueue();
184 // apply the closure to all elements in the task queue
185 void oops_do(OopClosure* f);
187 private:
188 // Element array.
189 volatile E* _elems;
190 };
192 template<class E, unsigned int N>
193 GenericTaskQueue<E, N>::GenericTaskQueue() {
194 assert(sizeof(Age) == sizeof(size_t), "Depends on this.");
195 }
197 template<class E, unsigned int N>
198 void GenericTaskQueue<E, N>::initialize() {
199 _elems = NEW_C_HEAP_ARRAY(E, N);
200 }
202 template<class E, unsigned int N>
203 void GenericTaskQueue<E, N>::oops_do(OopClosure* f) {
204 // tty->print_cr("START OopTaskQueue::oops_do");
205 uint iters = size();
206 uint index = _bottom;
207 for (uint i = 0; i < iters; ++i) {
208 index = decrement_index(index);
209 // tty->print_cr(" doing entry %d," INTPTR_T " -> " INTPTR_T,
210 // index, &_elems[index], _elems[index]);
211 E* t = (E*)&_elems[index]; // cast away volatility
212 oop* p = (oop*)t;
213 assert((*t)->is_oop_or_null(), "Not an oop or null");
214 f->do_oop(p);
215 }
216 // tty->print_cr("END OopTaskQueue::oops_do");
217 }
219 template<class E, unsigned int N>
220 bool GenericTaskQueue<E, N>::push_slow(E t, uint dirty_n_elems) {
221 if (dirty_n_elems == N - 1) {
222 // Actually means 0, so do the push.
223 uint localBot = _bottom;
224 // g++ complains if the volatile result of the assignment is unused.
225 const_cast<E&>(_elems[localBot] = t);
226 OrderAccess::release_store(&_bottom, increment_index(localBot));
227 return true;
228 }
229 return false;
230 }
232 template<class E, unsigned int N>
233 bool GenericTaskQueue<E, N>::
234 pop_local_slow(uint localBot, Age oldAge) {
235 // This queue was observed to contain exactly one element; either this
236 // thread will claim it, or a competing "pop_global". In either case,
237 // the queue will be logically empty afterwards. Create a new Age value
238 // that represents the empty queue for the given value of "_bottom". (We
239 // must also increment "tag" because of the case where "bottom == 1",
240 // "top == 0". A pop_global could read the queue element in that case,
241 // then have the owner thread do a pop followed by another push. Without
242 // the incrementing of "tag", the pop_global's CAS could succeed,
243 // allowing it to believe it has claimed the stale element.)
244 Age newAge((idx_t)localBot, oldAge.tag() + 1);
245 // Perhaps a competing pop_global has already incremented "top", in which
246 // case it wins the element.
247 if (localBot == oldAge.top()) {
248 // No competing pop_global has yet incremented "top"; we'll try to
249 // install new_age, thus claiming the element.
250 Age tempAge = _age.cmpxchg(newAge, oldAge);
251 if (tempAge == oldAge) {
252 // We win.
253 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
254 return true;
255 }
256 }
257 // We lose; a completing pop_global gets the element. But the queue is empty
258 // and top is greater than bottom. Fix this representation of the empty queue
259 // to become the canonical one.
260 _age.set(newAge);
261 assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
262 return false;
263 }
265 template<class E, unsigned int N>
266 bool GenericTaskQueue<E, N>::pop_global(E& t) {
267 Age oldAge = _age.get();
268 uint localBot = _bottom;
269 uint n_elems = size(localBot, oldAge.top());
270 if (n_elems == 0) {
271 return false;
272 }
274 const_cast<E&>(t = _elems[oldAge.top()]);
275 Age newAge(oldAge);
276 newAge.increment();
277 Age resAge = _age.cmpxchg(newAge, oldAge);
279 // Note that using "_bottom" here might fail, since a pop_local might
280 // have decremented it.
281 assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
282 return resAge == oldAge;
283 }
285 template<class E, unsigned int N>
286 GenericTaskQueue<E, N>::~GenericTaskQueue() {
287 FREE_C_HEAP_ARRAY(E, _elems);
288 }
290 // OverflowTaskQueue is a TaskQueue that also includes an overflow stack for
291 // elements that do not fit in the TaskQueue.
292 //
293 // Three methods from super classes are overridden:
294 //
295 // initialize() - initialize the super classes and create the overflow stack
296 // push() - push onto the task queue or, if that fails, onto the overflow stack
297 // is_empty() - return true if both the TaskQueue and overflow stack are empty
298 //
299 // Note that size() is not overridden--it returns the number of elements in the
300 // TaskQueue, and does not include the size of the overflow stack. This
301 // simplifies replacement of GenericTaskQueues with OverflowTaskQueues.
302 template<class E, unsigned int N = TASKQUEUE_SIZE>
303 class OverflowTaskQueue: public GenericTaskQueue<E, N>
304 {
305 public:
306 typedef GrowableArray<E> overflow_t;
307 typedef GenericTaskQueue<E, N> taskqueue_t;
309 OverflowTaskQueue();
310 ~OverflowTaskQueue();
311 void initialize();
313 inline overflow_t* overflow_stack() const { return _overflow_stack; }
315 // Push task t onto the queue or onto the overflow stack. Return true.
316 inline bool push(E t);
318 // Attempt to pop from the overflow stack; return true if anything was popped.
319 inline bool pop_overflow(E& t);
321 inline bool taskqueue_empty() const { return taskqueue_t::is_empty(); }
322 inline bool overflow_empty() const { return overflow_stack()->is_empty(); }
323 inline bool is_empty() const {
324 return taskqueue_empty() && overflow_empty();
325 }
327 private:
328 overflow_t* _overflow_stack;
329 };
331 template <class E, unsigned int N>
332 OverflowTaskQueue<E, N>::OverflowTaskQueue()
333 {
334 _overflow_stack = NULL;
335 }
337 template <class E, unsigned int N>
338 OverflowTaskQueue<E, N>::~OverflowTaskQueue()
339 {
340 if (_overflow_stack != NULL) {
341 delete _overflow_stack;
342 _overflow_stack = NULL;
343 }
344 }
346 template <class E, unsigned int N>
347 void OverflowTaskQueue<E, N>::initialize()
348 {
349 taskqueue_t::initialize();
350 assert(_overflow_stack == NULL, "memory leak");
351 _overflow_stack = new (ResourceObj::C_HEAP) GrowableArray<E>(10, true);
352 }
354 template <class E, unsigned int N>
355 bool OverflowTaskQueue<E, N>::push(E t)
356 {
357 if (!taskqueue_t::push(t)) {
358 overflow_stack()->push(t);
359 }
360 return true;
361 }
363 template <class E, unsigned int N>
364 bool OverflowTaskQueue<E, N>::pop_overflow(E& t)
365 {
366 if (overflow_empty()) return false;
367 t = overflow_stack()->pop();
368 return true;
369 }
371 class TaskQueueSetSuper: public CHeapObj {
372 protected:
373 static int randomParkAndMiller(int* seed0);
374 public:
375 // Returns "true" if some TaskQueue in the set contains a task.
376 virtual bool peek() = 0;
377 };
379 template<class T>
380 class GenericTaskQueueSet: public TaskQueueSetSuper {
381 private:
382 uint _n;
383 T** _queues;
385 public:
386 typedef typename T::element_type E;
388 GenericTaskQueueSet(int n) : _n(n) {
389 typedef T* GenericTaskQueuePtr;
390 _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n);
391 for (int i = 0; i < n; i++) {
392 _queues[i] = NULL;
393 }
394 }
396 bool steal_1_random(uint queue_num, int* seed, E& t);
397 bool steal_best_of_2(uint queue_num, int* seed, E& t);
398 bool steal_best_of_all(uint queue_num, int* seed, E& t);
400 void register_queue(uint i, T* q);
402 T* queue(uint n);
404 // The thread with queue number "queue_num" (and whose random number seed is
405 // at "seed") is trying to steal a task from some other queue. (It may try
406 // several queues, according to some configuration parameter.) If some steal
407 // succeeds, returns "true" and sets "t" to the stolen task, otherwise returns
408 // false.
409 bool steal(uint queue_num, int* seed, E& t);
411 bool peek();
412 };
414 template<class T> void
415 GenericTaskQueueSet<T>::register_queue(uint i, T* q) {
416 assert(i < _n, "index out of range.");
417 _queues[i] = q;
418 }
420 template<class T> T*
421 GenericTaskQueueSet<T>::queue(uint i) {
422 return _queues[i];
423 }
425 template<class T> bool
426 GenericTaskQueueSet<T>::steal(uint queue_num, int* seed, E& t) {
427 for (uint i = 0; i < 2 * _n; i++)
428 if (steal_best_of_2(queue_num, seed, t))
429 return true;
430 return false;
431 }
433 template<class T> bool
434 GenericTaskQueueSet<T>::steal_best_of_all(uint queue_num, int* seed, E& t) {
435 if (_n > 2) {
436 int best_k;
437 uint best_sz = 0;
438 for (uint k = 0; k < _n; k++) {
439 if (k == queue_num) continue;
440 uint sz = _queues[k]->size();
441 if (sz > best_sz) {
442 best_sz = sz;
443 best_k = k;
444 }
445 }
446 return best_sz > 0 && _queues[best_k]->pop_global(t);
447 } else if (_n == 2) {
448 // Just try the other one.
449 int k = (queue_num + 1) % 2;
450 return _queues[k]->pop_global(t);
451 } else {
452 assert(_n == 1, "can't be zero.");
453 return false;
454 }
455 }
457 template<class T> bool
458 GenericTaskQueueSet<T>::steal_1_random(uint queue_num, int* seed, E& t) {
459 if (_n > 2) {
460 uint k = queue_num;
461 while (k == queue_num) k = randomParkAndMiller(seed) % _n;
462 return _queues[2]->pop_global(t);
463 } else if (_n == 2) {
464 // Just try the other one.
465 int k = (queue_num + 1) % 2;
466 return _queues[k]->pop_global(t);
467 } else {
468 assert(_n == 1, "can't be zero.");
469 return false;
470 }
471 }
473 template<class T> bool
474 GenericTaskQueueSet<T>::steal_best_of_2(uint queue_num, int* seed, E& t) {
475 if (_n > 2) {
476 uint k1 = queue_num;
477 while (k1 == queue_num) k1 = randomParkAndMiller(seed) % _n;
478 uint k2 = queue_num;
479 while (k2 == queue_num || k2 == k1) k2 = randomParkAndMiller(seed) % _n;
480 // Sample both and try the larger.
481 uint sz1 = _queues[k1]->size();
482 uint sz2 = _queues[k2]->size();
483 if (sz2 > sz1) return _queues[k2]->pop_global(t);
484 else return _queues[k1]->pop_global(t);
485 } else if (_n == 2) {
486 // Just try the other one.
487 uint k = (queue_num + 1) % 2;
488 return _queues[k]->pop_global(t);
489 } else {
490 assert(_n == 1, "can't be zero.");
491 return false;
492 }
493 }
495 template<class T>
496 bool GenericTaskQueueSet<T>::peek() {
497 // Try all the queues.
498 for (uint j = 0; j < _n; j++) {
499 if (_queues[j]->peek())
500 return true;
501 }
502 return false;
503 }
505 // When to terminate from the termination protocol.
506 class TerminatorTerminator: public CHeapObj {
507 public:
508 virtual bool should_exit_termination() = 0;
509 };
511 // A class to aid in the termination of a set of parallel tasks using
512 // TaskQueueSet's for work stealing.
514 #undef TRACESPINNING
516 class ParallelTaskTerminator: public StackObj {
517 private:
518 int _n_threads;
519 TaskQueueSetSuper* _queue_set;
520 int _offered_termination;
522 #ifdef TRACESPINNING
523 static uint _total_yields;
524 static uint _total_spins;
525 static uint _total_peeks;
526 #endif
528 bool peek_in_queue_set();
529 protected:
530 virtual void yield();
531 void sleep(uint millis);
533 public:
535 // "n_threads" is the number of threads to be terminated. "queue_set" is a
536 // queue sets of work queues of other threads.
537 ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
539 // The current thread has no work, and is ready to terminate if everyone
540 // else is. If returns "true", all threads are terminated. If returns
541 // "false", available work has been observed in one of the task queues,
542 // so the global task is not complete.
543 bool offer_termination() {
544 return offer_termination(NULL);
545 }
547 // As above, but it also terminates if the should_exit_termination()
548 // method of the terminator parameter returns true. If terminator is
549 // NULL, then it is ignored.
550 bool offer_termination(TerminatorTerminator* terminator);
552 // Reset the terminator, so that it may be reused again.
553 // The caller is responsible for ensuring that this is done
554 // in an MT-safe manner, once the previous round of use of
555 // the terminator is finished.
556 void reset_for_reuse();
558 #ifdef TRACESPINNING
559 static uint total_yields() { return _total_yields; }
560 static uint total_spins() { return _total_spins; }
561 static uint total_peeks() { return _total_peeks; }
562 static void print_termination_counts();
563 #endif
564 };
566 template<class E, unsigned int N> inline bool
567 GenericTaskQueue<E, N>::push(E t) {
568 uint localBot = _bottom;
569 assert((localBot >= 0) && (localBot < N), "_bottom out of range.");
570 idx_t top = _age.top();
571 uint dirty_n_elems = dirty_size(localBot, top);
572 assert(dirty_n_elems < N, "n_elems out of range.");
573 if (dirty_n_elems < max_elems()) {
574 // g++ complains if the volatile result of the assignment is unused.
575 const_cast<E&>(_elems[localBot] = t);
576 OrderAccess::release_store(&_bottom, increment_index(localBot));
577 return true;
578 } else {
579 return push_slow(t, dirty_n_elems);
580 }
581 }
583 template<class E, unsigned int N> inline bool
584 GenericTaskQueue<E, N>::pop_local(E& t) {
585 uint localBot = _bottom;
586 // This value cannot be N-1. That can only occur as a result of
587 // the assignment to bottom in this method. If it does, this method
588 // resets the size to 0 before the next call (which is sequential,
589 // since this is pop_local.)
590 uint dirty_n_elems = dirty_size(localBot, _age.top());
591 assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
592 if (dirty_n_elems == 0) return false;
593 localBot = decrement_index(localBot);
594 _bottom = localBot;
595 // This is necessary to prevent any read below from being reordered
596 // before the store just above.
597 OrderAccess::fence();
598 const_cast<E&>(t = _elems[localBot]);
599 // This is a second read of "age"; the "size()" above is the first.
600 // If there's still at least one element in the queue, based on the
601 // "_bottom" and "age" we've read, then there can be no interference with
602 // a "pop_global" operation, and we're done.
603 idx_t tp = _age.top(); // XXX
604 if (size(localBot, tp) > 0) {
605 assert(dirty_size(localBot, tp) != N - 1, "sanity");
606 return true;
607 } else {
608 // Otherwise, the queue contained exactly one element; we take the slow
609 // path.
610 return pop_local_slow(localBot, _age.get());
611 }
612 }
614 typedef GenericTaskQueue<oop> OopTaskQueue;
615 typedef GenericTaskQueueSet<OopTaskQueue> OopTaskQueueSet;
617 #ifdef _MSC_VER
618 #pragma warning(push)
619 // warning C4522: multiple assignment operators specified
620 #pragma warning(disable:4522)
621 #endif
623 // This is a container class for either an oop* or a narrowOop*.
624 // Both are pushed onto a task queue and the consumer will test is_narrow()
625 // to determine which should be processed.
626 class StarTask {
627 void* _holder; // either union oop* or narrowOop*
629 enum { COMPRESSED_OOP_MASK = 1 };
631 public:
632 StarTask(narrowOop* p) {
633 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
634 _holder = (void *)((uintptr_t)p | COMPRESSED_OOP_MASK);
635 }
636 StarTask(oop* p) {
637 assert(((uintptr_t)p & COMPRESSED_OOP_MASK) == 0, "Information loss!");
638 _holder = (void*)p;
639 }
640 StarTask() { _holder = NULL; }
641 operator oop*() { return (oop*)_holder; }
642 operator narrowOop*() {
643 return (narrowOop*)((uintptr_t)_holder & ~COMPRESSED_OOP_MASK);
644 }
646 StarTask& operator=(const StarTask& t) {
647 _holder = t._holder;
648 return *this;
649 }
650 volatile StarTask& operator=(const volatile StarTask& t) volatile {
651 _holder = t._holder;
652 return *this;
653 }
655 bool is_narrow() const {
656 return (((uintptr_t)_holder & COMPRESSED_OOP_MASK) != 0);
657 }
658 };
660 class ObjArrayTask
661 {
662 public:
663 ObjArrayTask(oop o = NULL, int idx = 0): _obj(o), _index(idx) { }
664 ObjArrayTask(oop o, size_t idx): _obj(o), _index(int(idx)) {
665 assert(idx <= size_t(max_jint), "too big");
666 }
667 ObjArrayTask(const ObjArrayTask& t): _obj(t._obj), _index(t._index) { }
669 ObjArrayTask& operator =(const ObjArrayTask& t) {
670 _obj = t._obj;
671 _index = t._index;
672 return *this;
673 }
674 volatile ObjArrayTask&
675 operator =(const volatile ObjArrayTask& t) volatile {
676 _obj = t._obj;
677 _index = t._index;
678 return *this;
679 }
681 inline oop obj() const { return _obj; }
682 inline int index() const { return _index; }
684 DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
686 private:
687 oop _obj;
688 int _index;
689 };
691 #ifdef _MSC_VER
692 #pragma warning(pop)
693 #endif
695 typedef OverflowTaskQueue<StarTask> OopStarTaskQueue;
696 typedef GenericTaskQueueSet<OopStarTaskQueue> OopStarTaskQueueSet;
698 typedef OverflowTaskQueue<size_t> RegionTaskQueue;
699 typedef GenericTaskQueueSet<RegionTaskQueue> RegionTaskQueueSet;