| /* |
| * Copyright 2001-2006 Sun Microsystems, Inc. All Rights Reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| * CA 95054 USA or visit www.sun.com if you need additional information or |
| * have any questions. |
| * |
| */ |
| |
| class TaskQueueSuper: public CHeapObj { |
| protected: |
| // The first free element after the last one pushed (mod _n). |
| // (For now we'll assume only 32-bit CAS). |
| volatile juint _bottom; |
| |
| // log2 of the size of the queue. |
| enum SomeProtectedConstants { |
| Log_n = 14 |
| }; |
| |
| // Size of the queue. |
| juint n() { return (1 << Log_n); } |
| // For computing "x mod n" efficiently. |
| juint n_mod_mask() { return n() - 1; } |
| |
| struct Age { |
| jushort _top; |
| jushort _tag; |
| |
| jushort tag() const { return _tag; } |
| jushort top() const { return _top; } |
| |
| Age() { _tag = 0; _top = 0; } |
| |
| friend bool operator ==(const Age& a1, const Age& a2) { |
| return a1.tag() == a2.tag() && a1.top() == a2.top(); |
| } |
| |
| }; |
| Age _age; |
| // These make sure we do single atomic reads and writes. |
| Age get_age() { |
| jint res = *(volatile jint*)(&_age); |
| return *(Age*)(&res); |
| } |
| void set_age(Age a) { |
| *(volatile jint*)(&_age) = *(int*)(&a); |
| } |
| |
| jushort get_top() { |
| return get_age().top(); |
| } |
| |
| // These both operate mod _n. |
| juint increment_index(juint ind) { |
| return (ind + 1) & n_mod_mask(); |
| } |
| juint decrement_index(juint ind) { |
| return (ind - 1) & n_mod_mask(); |
| } |
| |
| // Returns a number in the range [0.._n). If the result is "n-1", it |
| // should be interpreted as 0. |
| juint dirty_size(juint bot, juint top) { |
| return ((jint)bot - (jint)top) & n_mod_mask(); |
| } |
| |
| // Returns the size corresponding to the given "bot" and "top". |
| juint size(juint bot, juint top) { |
| juint sz = dirty_size(bot, top); |
| // Has the queue "wrapped", so that bottom is less than top? |
| // There's a complicated special case here. A pair of threads could |
| // perform pop_local and pop_global operations concurrently, starting |
| // from a state in which _bottom == _top+1. The pop_local could |
| // succeed in decrementing _bottom, and the pop_global in incrementing |
| // _top (in which case the pop_global will be awarded the contested |
| // queue element.) The resulting state must be interpreted as an empty |
| // queue. (We only need to worry about one such event: only the queue |
| // owner performs pop_local's, and several concurrent threads |
| // attempting to perform the pop_global will all perform the same CAS, |
| // and only one can succeed. Any stealing thread that reads after |
| // either the increment or decrement will seen an empty queue, and will |
| // not join the competitors. The "sz == -1 || sz == _n-1" state will |
| // not be modified by concurrent queues, so the owner thread can reset |
| // the state to _bottom == top so subsequent pushes will be performed |
| // normally. |
| if (sz == (n()-1)) return 0; |
| else return sz; |
| } |
| |
| public: |
| TaskQueueSuper() : _bottom(0), _age() {} |
| |
| // Return "true" if the TaskQueue contains any tasks. |
| bool peek(); |
| |
| // Return an estimate of the number of elements in the queue. |
| // The "careful" version admits the possibility of pop_local/pop_global |
| // races. |
| juint size() { |
| return size(_bottom, get_top()); |
| } |
| |
| juint dirty_size() { |
| return dirty_size(_bottom, get_top()); |
| } |
| |
| // Maximum number of elements allowed in the queue. This is two less |
| // than the actual queue size, for somewhat complicated reasons. |
| juint max_elems() { return n() - 2; } |
| |
| }; |
| |
| template<class E> class GenericTaskQueue: public TaskQueueSuper { |
| private: |
| // Slow paths for push, pop_local. (pop_global has no fast path.) |
| bool push_slow(E t, juint dirty_n_elems); |
| bool pop_local_slow(juint localBot, Age oldAge); |
| |
| public: |
| // Initializes the queue to empty. |
| GenericTaskQueue(); |
| |
| void initialize(); |
| |
| // Push the task "t" on the queue. Returns "false" iff the queue is |
| // full. |
| inline bool push(E t); |
| |
| // If succeeds in claiming a task (from the 'local' end, that is, the |
| // most recently pushed task), returns "true" and sets "t" to that task. |
| // Otherwise, the queue is empty and returns false. |
| inline bool pop_local(E& t); |
| |
| // If succeeds in claiming a task (from the 'global' end, that is, the |
| // least recently pushed task), returns "true" and sets "t" to that task. |
| // Otherwise, the queue is empty and returns false. |
| bool pop_global(E& t); |
| |
| // Delete any resource associated with the queue. |
| ~GenericTaskQueue(); |
| |
| private: |
| // Element array. |
| volatile E* _elems; |
| }; |
| |
| template<class E> |
| GenericTaskQueue<E>::GenericTaskQueue():TaskQueueSuper() { |
| assert(sizeof(Age) == sizeof(jint), "Depends on this."); |
| } |
| |
| template<class E> |
| void GenericTaskQueue<E>::initialize() { |
| _elems = NEW_C_HEAP_ARRAY(E, n()); |
| guarantee(_elems != NULL, "Allocation failed."); |
| } |
| |
| template<class E> |
| bool GenericTaskQueue<E>::push_slow(E t, juint dirty_n_elems) { |
| if (dirty_n_elems == n() - 1) { |
| // Actually means 0, so do the push. |
| juint localBot = _bottom; |
| _elems[localBot] = t; |
| _bottom = increment_index(localBot); |
| return true; |
| } else |
| return false; |
| } |
| |
| template<class E> |
| bool GenericTaskQueue<E>:: |
| pop_local_slow(juint localBot, Age oldAge) { |
| // This queue was observed to contain exactly one element; either this |
| // thread will claim it, or a competing "pop_global". In either case, |
| // the queue will be logically empty afterwards. Create a new Age value |
| // that represents the empty queue for the given value of "_bottom". (We |
| // must also increment "tag" because of the case where "bottom == 1", |
| // "top == 0". A pop_global could read the queue element in that case, |
| // then have the owner thread do a pop followed by another push. Without |
| // the incrementing of "tag", the pop_global's CAS could succeed, |
| // allowing it to believe it has claimed the stale element.) |
| Age newAge; |
| newAge._top = localBot; |
| newAge._tag = oldAge.tag() + 1; |
| // Perhaps a competing pop_global has already incremented "top", in which |
| // case it wins the element. |
| if (localBot == oldAge.top()) { |
| Age tempAge; |
| // No competing pop_global has yet incremented "top"; we'll try to |
| // install new_age, thus claiming the element. |
| assert(sizeof(Age) == sizeof(jint) && sizeof(jint) == sizeof(juint), |
| "Assumption about CAS unit."); |
| *(jint*)&tempAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge); |
| if (tempAge == oldAge) { |
| // We win. |
| assert(dirty_size(localBot, get_top()) != n() - 1, |
| "Shouldn't be possible..."); |
| return true; |
| } |
| } |
| // We fail; a completing pop_global gets the element. But the queue is |
| // empty (and top is greater than bottom.) Fix this representation of |
| // the empty queue to become the canonical one. |
| set_age(newAge); |
| assert(dirty_size(localBot, get_top()) != n() - 1, |
| "Shouldn't be possible..."); |
| return false; |
| } |
| |
| template<class E> |
| bool GenericTaskQueue<E>::pop_global(E& t) { |
| Age newAge; |
| Age oldAge = get_age(); |
| juint localBot = _bottom; |
| juint n_elems = size(localBot, oldAge.top()); |
| if (n_elems == 0) { |
| return false; |
| } |
| t = _elems[oldAge.top()]; |
| newAge = oldAge; |
| newAge._top = increment_index(newAge.top()); |
| if ( newAge._top == 0 ) newAge._tag++; |
| Age resAge; |
| *(jint*)&resAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge); |
| // Note that using "_bottom" here might fail, since a pop_local might |
| // have decremented it. |
| assert(dirty_size(localBot, newAge._top) != n() - 1, |
| "Shouldn't be possible..."); |
| return (resAge == oldAge); |
| } |
| |
| template<class E> |
| GenericTaskQueue<E>::~GenericTaskQueue() { |
| FREE_C_HEAP_ARRAY(E, _elems); |
| } |
| |
| // Inherits the typedef of "Task" from above. |
| class TaskQueueSetSuper: public CHeapObj { |
| protected: |
| static int randomParkAndMiller(int* seed0); |
| public: |
| // Returns "true" if some TaskQueue in the set contains a task. |
| virtual bool peek() = 0; |
| }; |
| |
| template<class E> class GenericTaskQueueSet: public TaskQueueSetSuper { |
| private: |
| int _n; |
| GenericTaskQueue<E>** _queues; |
| |
| public: |
| GenericTaskQueueSet(int n) : _n(n) { |
| typedef GenericTaskQueue<E>* GenericTaskQueuePtr; |
| _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n); |
| guarantee(_queues != NULL, "Allocation failure."); |
| for (int i = 0; i < n; i++) { |
| _queues[i] = NULL; |
| } |
| } |
| |
| bool steal_1_random(int queue_num, int* seed, E& t); |
| bool steal_best_of_2(int queue_num, int* seed, E& t); |
| bool steal_best_of_all(int queue_num, int* seed, E& t); |
| |
| void register_queue(int i, GenericTaskQueue<E>* q); |
| |
| GenericTaskQueue<E>* queue(int n); |
| |
| // The thread with queue number "queue_num" (and whose random number seed |
| // is at "seed") is trying to steal a task from some other queue. (It |
| // may try several queues, according to some configuration parameter.) |
| // If some steal succeeds, returns "true" and sets "t" the stolen task, |
| // otherwise returns false. |
| bool steal(int queue_num, int* seed, E& t); |
| |
| bool peek(); |
| }; |
| |
| template<class E> |
| void GenericTaskQueueSet<E>::register_queue(int i, GenericTaskQueue<E>* q) { |
| assert(0 <= i && i < _n, "index out of range."); |
| _queues[i] = q; |
| } |
| |
| template<class E> |
| GenericTaskQueue<E>* GenericTaskQueueSet<E>::queue(int i) { |
| return _queues[i]; |
| } |
| |
| template<class E> |
| bool GenericTaskQueueSet<E>::steal(int queue_num, int* seed, E& t) { |
| for (int i = 0; i < 2 * _n; i++) |
| if (steal_best_of_2(queue_num, seed, t)) |
| return true; |
| return false; |
| } |
| |
| template<class E> |
| bool GenericTaskQueueSet<E>::steal_best_of_all(int queue_num, int* seed, E& t) { |
| if (_n > 2) { |
| int best_k; |
| jint best_sz = 0; |
| for (int k = 0; k < _n; k++) { |
| if (k == queue_num) continue; |
| jint sz = _queues[k]->size(); |
| if (sz > best_sz) { |
| best_sz = sz; |
| best_k = k; |
| } |
| } |
| return best_sz > 0 && _queues[best_k]->pop_global(t); |
| } else if (_n == 2) { |
| // Just try the other one. |
| int k = (queue_num + 1) % 2; |
| return _queues[k]->pop_global(t); |
| } else { |
| assert(_n == 1, "can't be zero."); |
| return false; |
| } |
| } |
| |
| template<class E> |
| bool GenericTaskQueueSet<E>::steal_1_random(int queue_num, int* seed, E& t) { |
| if (_n > 2) { |
| int k = queue_num; |
| while (k == queue_num) k = randomParkAndMiller(seed) % _n; |
| return _queues[2]->pop_global(t); |
| } else if (_n == 2) { |
| // Just try the other one. |
| int k = (queue_num + 1) % 2; |
| return _queues[k]->pop_global(t); |
| } else { |
| assert(_n == 1, "can't be zero."); |
| return false; |
| } |
| } |
| |
| template<class E> |
| bool GenericTaskQueueSet<E>::steal_best_of_2(int queue_num, int* seed, E& t) { |
| if (_n > 2) { |
| int k1 = queue_num; |
| while (k1 == queue_num) k1 = randomParkAndMiller(seed) % _n; |
| int k2 = queue_num; |
| while (k2 == queue_num || k2 == k1) k2 = randomParkAndMiller(seed) % _n; |
| // Sample both and try the larger. |
| juint sz1 = _queues[k1]->size(); |
| juint sz2 = _queues[k2]->size(); |
| if (sz2 > sz1) return _queues[k2]->pop_global(t); |
| else return _queues[k1]->pop_global(t); |
| } else if (_n == 2) { |
| // Just try the other one. |
| int k = (queue_num + 1) % 2; |
| return _queues[k]->pop_global(t); |
| } else { |
| assert(_n == 1, "can't be zero."); |
| return false; |
| } |
| } |
| |
| template<class E> |
| bool GenericTaskQueueSet<E>::peek() { |
| // Try all the queues. |
| for (int j = 0; j < _n; j++) { |
| if (_queues[j]->peek()) |
| return true; |
| } |
| return false; |
| } |
| |
| // A class to aid in the termination of a set of parallel tasks using |
| // TaskQueueSet's for work stealing. |
| |
| class ParallelTaskTerminator: public StackObj { |
| private: |
| int _n_threads; |
| TaskQueueSetSuper* _queue_set; |
| jint _offered_termination; |
| |
| bool peek_in_queue_set(); |
| protected: |
| virtual void yield(); |
| void sleep(uint millis); |
| |
| public: |
| |
| // "n_threads" is the number of threads to be terminated. "queue_set" is a |
| // queue sets of work queues of other threads. |
| ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set); |
| |
| // The current thread has no work, and is ready to terminate if everyone |
| // else is. If returns "true", all threads are terminated. If returns |
| // "false", available work has been observed in one of the task queues, |
| // so the global task is not complete. |
| bool offer_termination(); |
| |
| // Reset the terminator, so that it may be reused again. |
| // The caller is responsible for ensuring that this is done |
| // in an MT-safe manner, once the previous round of use of |
| // the terminator is finished. |
| void reset_for_reuse(); |
| |
| }; |
| |
| #define SIMPLE_STACK 0 |
| |
| template<class E> inline bool GenericTaskQueue<E>::push(E t) { |
| #if SIMPLE_STACK |
| juint localBot = _bottom; |
| if (_bottom < max_elems()) { |
| _elems[localBot] = t; |
| _bottom = localBot + 1; |
| return true; |
| } else { |
| return false; |
| } |
| #else |
| juint localBot = _bottom; |
| assert((localBot >= 0) && (localBot < n()), "_bottom out of range."); |
| jushort top = get_top(); |
| juint dirty_n_elems = dirty_size(localBot, top); |
| assert((dirty_n_elems >= 0) && (dirty_n_elems < n()), |
| "n_elems out of range."); |
| if (dirty_n_elems < max_elems()) { |
| _elems[localBot] = t; |
| _bottom = increment_index(localBot); |
| return true; |
| } else { |
| return push_slow(t, dirty_n_elems); |
| } |
| #endif |
| } |
| |
| template<class E> inline bool GenericTaskQueue<E>::pop_local(E& t) { |
| #if SIMPLE_STACK |
| juint localBot = _bottom; |
| assert(localBot > 0, "precondition."); |
| localBot--; |
| t = _elems[localBot]; |
| _bottom = localBot; |
| return true; |
| #else |
| juint localBot = _bottom; |
| // This value cannot be n-1. That can only occur as a result of |
| // the assignment to bottom in this method. If it does, this method |
| // resets the size( to 0 before the next call (which is sequential, |
| // since this is pop_local.) |
| juint dirty_n_elems = dirty_size(localBot, get_top()); |
| assert(dirty_n_elems != n() - 1, "Shouldn't be possible..."); |
| if (dirty_n_elems == 0) return false; |
| localBot = decrement_index(localBot); |
| _bottom = localBot; |
| // This is necessary to prevent any read below from being reordered |
| // before the store just above. |
| OrderAccess::fence(); |
| t = _elems[localBot]; |
| // This is a second read of "age"; the "size()" above is the first. |
| // If there's still at least one element in the queue, based on the |
| // "_bottom" and "age" we've read, then there can be no interference with |
| // a "pop_global" operation, and we're done. |
| juint tp = get_top(); |
| if (size(localBot, tp) > 0) { |
| assert(dirty_size(localBot, tp) != n() - 1, |
| "Shouldn't be possible..."); |
| return true; |
| } else { |
| // Otherwise, the queue contained exactly one element; we take the slow |
| // path. |
| return pop_local_slow(localBot, get_age()); |
| } |
| #endif |
| } |
| |
| typedef oop Task; |
| typedef GenericTaskQueue<Task> OopTaskQueue; |
| typedef GenericTaskQueueSet<Task> OopTaskQueueSet; |
| |
| typedef oop* StarTask; |
| typedef GenericTaskQueue<StarTask> OopStarTaskQueue; |
| typedef GenericTaskQueueSet<StarTask> OopStarTaskQueueSet; |
| |
| typedef size_t ChunkTask; // index for chunk |
| typedef GenericTaskQueue<ChunkTask> ChunkTaskQueue; |
| typedef GenericTaskQueueSet<ChunkTask> ChunkTaskQueueSet; |
| |
| class ChunkTaskQueueWithOverflow: public CHeapObj { |
| protected: |
| ChunkTaskQueue _chunk_queue; |
| GrowableArray<ChunkTask>* _overflow_stack; |
| |
| public: |
| ChunkTaskQueueWithOverflow() : _overflow_stack(NULL) {} |
| // Initialize both stealable queue and overflow |
| void initialize(); |
| // Save first to stealable queue and then to overflow |
| void save(ChunkTask t); |
| // Retrieve first from overflow and then from stealable queue |
| bool retrieve(ChunkTask& chunk_index); |
| // Retrieve from stealable queue |
| bool retrieve_from_stealable_queue(ChunkTask& chunk_index); |
| // Retrieve from overflow |
| bool retrieve_from_overflow(ChunkTask& chunk_index); |
| bool is_empty(); |
| bool stealable_is_empty(); |
| bool overflow_is_empty(); |
| juint stealable_size() { return _chunk_queue.size(); } |
| ChunkTaskQueue* task_queue() { return &_chunk_queue; } |
| }; |
| |
| #define USE_ChunkTaskQueueWithOverflow |