--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/utilities/taskqueue.hpp Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,525 @@
+/*
+ * 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