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/*
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* Copyright 2001-2006 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*
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*/
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class TaskQueueSuper: public CHeapObj {
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protected:
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// The first free element after the last one pushed (mod _n).
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// (For now we'll assume only 32-bit CAS).
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volatile juint _bottom;
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// log2 of the size of the queue.
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enum SomeProtectedConstants {
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Log_n = 14
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};
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// Size of the queue.
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juint n() { return (1 << Log_n); }
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// For computing "x mod n" efficiently.
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juint n_mod_mask() { return n() - 1; }
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struct Age {
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jushort _top;
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jushort _tag;
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jushort tag() const { return _tag; }
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jushort top() const { return _top; }
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Age() { _tag = 0; _top = 0; }
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friend bool operator ==(const Age& a1, const Age& a2) {
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return a1.tag() == a2.tag() && a1.top() == a2.top();
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}
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};
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Age _age;
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// These make sure we do single atomic reads and writes.
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Age get_age() {
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jint res = *(volatile jint*)(&_age);
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return *(Age*)(&res);
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}
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void set_age(Age a) {
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*(volatile jint*)(&_age) = *(int*)(&a);
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}
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jushort get_top() {
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return get_age().top();
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}
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// These both operate mod _n.
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juint increment_index(juint ind) {
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return (ind + 1) & n_mod_mask();
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}
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juint decrement_index(juint ind) {
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return (ind - 1) & n_mod_mask();
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}
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// Returns a number in the range [0.._n). If the result is "n-1", it
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// should be interpreted as 0.
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juint dirty_size(juint bot, juint top) {
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return ((jint)bot - (jint)top) & n_mod_mask();
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}
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// Returns the size corresponding to the given "bot" and "top".
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juint size(juint bot, juint top) {
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juint sz = dirty_size(bot, top);
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// Has the queue "wrapped", so that bottom is less than top?
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// There's a complicated special case here. A pair of threads could
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// perform pop_local and pop_global operations concurrently, starting
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// from a state in which _bottom == _top+1. The pop_local could
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// succeed in decrementing _bottom, and the pop_global in incrementing
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// _top (in which case the pop_global will be awarded the contested
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// queue element.) The resulting state must be interpreted as an empty
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// queue. (We only need to worry about one such event: only the queue
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// owner performs pop_local's, and several concurrent threads
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// attempting to perform the pop_global will all perform the same CAS,
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// and only one can succeed. Any stealing thread that reads after
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// either the increment or decrement will seen an empty queue, and will
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// not join the competitors. The "sz == -1 || sz == _n-1" state will
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// not be modified by concurrent queues, so the owner thread can reset
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// the state to _bottom == top so subsequent pushes will be performed
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// normally.
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if (sz == (n()-1)) return 0;
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else return sz;
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}
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public:
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TaskQueueSuper() : _bottom(0), _age() {}
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// Return "true" if the TaskQueue contains any tasks.
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bool peek();
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// Return an estimate of the number of elements in the queue.
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// The "careful" version admits the possibility of pop_local/pop_global
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// races.
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juint size() {
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return size(_bottom, get_top());
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}
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juint dirty_size() {
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return dirty_size(_bottom, get_top());
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}
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// Maximum number of elements allowed in the queue. This is two less
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// than the actual queue size, for somewhat complicated reasons.
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juint max_elems() { return n() - 2; }
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};
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template<class E> class GenericTaskQueue: public TaskQueueSuper {
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private:
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// Slow paths for push, pop_local. (pop_global has no fast path.)
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bool push_slow(E t, juint dirty_n_elems);
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bool pop_local_slow(juint localBot, Age oldAge);
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public:
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// Initializes the queue to empty.
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GenericTaskQueue();
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void initialize();
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// Push the task "t" on the queue. Returns "false" iff the queue is
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// full.
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inline bool push(E t);
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// If succeeds in claiming a task (from the 'local' end, that is, the
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// most recently pushed task), returns "true" and sets "t" to that task.
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// Otherwise, the queue is empty and returns false.
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inline bool pop_local(E& t);
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// If succeeds in claiming a task (from the 'global' end, that is, the
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// least recently pushed task), returns "true" and sets "t" to that task.
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// Otherwise, the queue is empty and returns false.
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bool pop_global(E& t);
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// Delete any resource associated with the queue.
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~GenericTaskQueue();
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private:
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// Element array.
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volatile E* _elems;
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};
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template<class E>
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GenericTaskQueue<E>::GenericTaskQueue():TaskQueueSuper() {
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assert(sizeof(Age) == sizeof(jint), "Depends on this.");
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}
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template<class E>
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void GenericTaskQueue<E>::initialize() {
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_elems = NEW_C_HEAP_ARRAY(E, n());
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guarantee(_elems != NULL, "Allocation failed.");
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}
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template<class E>
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bool GenericTaskQueue<E>::push_slow(E t, juint dirty_n_elems) {
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if (dirty_n_elems == n() - 1) {
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// Actually means 0, so do the push.
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juint localBot = _bottom;
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_elems[localBot] = t;
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_bottom = increment_index(localBot);
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return true;
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} else
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return false;
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}
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template<class E>
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bool GenericTaskQueue<E>::
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pop_local_slow(juint localBot, Age oldAge) {
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// This queue was observed to contain exactly one element; either this
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// thread will claim it, or a competing "pop_global". In either case,
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// the queue will be logically empty afterwards. Create a new Age value
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// that represents the empty queue for the given value of "_bottom". (We
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// must also increment "tag" because of the case where "bottom == 1",
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// "top == 0". A pop_global could read the queue element in that case,
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// then have the owner thread do a pop followed by another push. Without
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// the incrementing of "tag", the pop_global's CAS could succeed,
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// allowing it to believe it has claimed the stale element.)
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Age newAge;
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newAge._top = localBot;
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newAge._tag = oldAge.tag() + 1;
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// Perhaps a competing pop_global has already incremented "top", in which
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// case it wins the element.
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if (localBot == oldAge.top()) {
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Age tempAge;
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// No competing pop_global has yet incremented "top"; we'll try to
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// install new_age, thus claiming the element.
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assert(sizeof(Age) == sizeof(jint) && sizeof(jint) == sizeof(juint),
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"Assumption about CAS unit.");
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*(jint*)&tempAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge);
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if (tempAge == oldAge) {
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// We win.
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assert(dirty_size(localBot, get_top()) != n() - 1,
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"Shouldn't be possible...");
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return true;
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}
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}
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// We fail; a completing pop_global gets the element. But the queue is
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// empty (and top is greater than bottom.) Fix this representation of
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// the empty queue to become the canonical one.
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set_age(newAge);
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assert(dirty_size(localBot, get_top()) != n() - 1,
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"Shouldn't be possible...");
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return false;
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}
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template<class E>
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bool GenericTaskQueue<E>::pop_global(E& t) {
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Age newAge;
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Age oldAge = get_age();
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juint localBot = _bottom;
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juint n_elems = size(localBot, oldAge.top());
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if (n_elems == 0) {
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return false;
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}
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t = _elems[oldAge.top()];
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newAge = oldAge;
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newAge._top = increment_index(newAge.top());
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if ( newAge._top == 0 ) newAge._tag++;
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Age resAge;
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*(jint*)&resAge = Atomic::cmpxchg(*(jint*)&newAge, (volatile jint*)&_age, *(jint*)&oldAge);
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// Note that using "_bottom" here might fail, since a pop_local might
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// have decremented it.
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assert(dirty_size(localBot, newAge._top) != n() - 1,
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"Shouldn't be possible...");
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return (resAge == oldAge);
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}
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template<class E>
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GenericTaskQueue<E>::~GenericTaskQueue() {
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FREE_C_HEAP_ARRAY(E, _elems);
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}
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// Inherits the typedef of "Task" from above.
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class TaskQueueSetSuper: public CHeapObj {
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protected:
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static int randomParkAndMiller(int* seed0);
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public:
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// Returns "true" if some TaskQueue in the set contains a task.
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virtual bool peek() = 0;
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};
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template<class E> class GenericTaskQueueSet: public TaskQueueSetSuper {
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private:
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int _n;
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GenericTaskQueue<E>** _queues;
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public:
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GenericTaskQueueSet(int n) : _n(n) {
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typedef GenericTaskQueue<E>* GenericTaskQueuePtr;
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_queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n);
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guarantee(_queues != NULL, "Allocation failure.");
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for (int i = 0; i < n; i++) {
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_queues[i] = NULL;
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}
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}
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bool steal_1_random(int queue_num, int* seed, E& t);
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bool steal_best_of_2(int queue_num, int* seed, E& t);
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bool steal_best_of_all(int queue_num, int* seed, E& t);
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void register_queue(int i, GenericTaskQueue<E>* q);
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GenericTaskQueue<E>* queue(int n);
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// The thread with queue number "queue_num" (and whose random number seed
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// is at "seed") is trying to steal a task from some other queue. (It
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// may try several queues, according to some configuration parameter.)
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// If some steal succeeds, returns "true" and sets "t" the stolen task,
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// otherwise returns false.
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bool steal(int queue_num, int* seed, E& t);
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bool peek();
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};
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template<class E>
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void GenericTaskQueueSet<E>::register_queue(int i, GenericTaskQueue<E>* q) {
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assert(0 <= i && i < _n, "index out of range.");
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_queues[i] = q;
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}
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template<class E>
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GenericTaskQueue<E>* GenericTaskQueueSet<E>::queue(int i) {
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return _queues[i];
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}
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template<class E>
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bool GenericTaskQueueSet<E>::steal(int queue_num, int* seed, E& t) {
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for (int i = 0; i < 2 * _n; i++)
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if (steal_best_of_2(queue_num, seed, t))
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return true;
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return false;
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}
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template<class E>
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bool GenericTaskQueueSet<E>::steal_best_of_all(int queue_num, int* seed, E& t) {
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if (_n > 2) {
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int best_k;
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jint best_sz = 0;
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for (int k = 0; k < _n; k++) {
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if (k == queue_num) continue;
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jint sz = _queues[k]->size();
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if (sz > best_sz) {
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best_sz = sz;
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best_k = k;
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}
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}
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return best_sz > 0 && _queues[best_k]->pop_global(t);
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} else if (_n == 2) {
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// Just try the other one.
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int k = (queue_num + 1) % 2;
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return _queues[k]->pop_global(t);
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} else {
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assert(_n == 1, "can't be zero.");
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return false;
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}
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}
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template<class E>
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bool GenericTaskQueueSet<E>::steal_1_random(int queue_num, int* seed, E& t) {
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if (_n > 2) {
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int k = queue_num;
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while (k == queue_num) k = randomParkAndMiller(seed) % _n;
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return _queues[2]->pop_global(t);
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} else if (_n == 2) {
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// Just try the other one.
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int k = (queue_num + 1) % 2;
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return _queues[k]->pop_global(t);
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} else {
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assert(_n == 1, "can't be zero.");
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return false;
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}
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}
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template<class E>
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bool GenericTaskQueueSet<E>::steal_best_of_2(int queue_num, int* seed, E& t) {
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if (_n > 2) {
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int k1 = queue_num;
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while (k1 == queue_num) k1 = randomParkAndMiller(seed) % _n;
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int k2 = queue_num;
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while (k2 == queue_num || k2 == k1) k2 = randomParkAndMiller(seed) % _n;
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// Sample both and try the larger.
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juint sz1 = _queues[k1]->size();
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juint sz2 = _queues[k2]->size();
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if (sz2 > sz1) return _queues[k2]->pop_global(t);
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else return _queues[k1]->pop_global(t);
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} else if (_n == 2) {
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// Just try the other one.
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int k = (queue_num + 1) % 2;
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return _queues[k]->pop_global(t);
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} else {
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assert(_n == 1, "can't be zero.");
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return false;
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}
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}
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template<class E>
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bool GenericTaskQueueSet<E>::peek() {
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// Try all the queues.
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for (int j = 0; j < _n; j++) {
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if (_queues[j]->peek())
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return true;
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}
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return false;
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}
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// A class to aid in the termination of a set of parallel tasks using
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// TaskQueueSet's for work stealing.
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class ParallelTaskTerminator: public StackObj {
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private:
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int _n_threads;
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TaskQueueSetSuper* _queue_set;
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jint _offered_termination;
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bool peek_in_queue_set();
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protected:
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virtual void yield();
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void sleep(uint millis);
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|
400 |
public:
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|
401 |
|
|
402 |
// "n_threads" is the number of threads to be terminated. "queue_set" is a
|
|
403 |
// queue sets of work queues of other threads.
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|
404 |
ParallelTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set);
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|
405 |
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|
406 |
// The current thread has no work, and is ready to terminate if everyone
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|
407 |
// else is. If returns "true", all threads are terminated. If returns
|
|
408 |
// "false", available work has been observed in one of the task queues,
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|
409 |
// so the global task is not complete.
|
|
410 |
bool offer_termination();
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|
411 |
|
|
412 |
// Reset the terminator, so that it may be reused again.
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|
413 |
// The caller is responsible for ensuring that this is done
|
|
414 |
// in an MT-safe manner, once the previous round of use of
|
|
415 |
// the terminator is finished.
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|
416 |
void reset_for_reuse();
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|
417 |
|
|
418 |
};
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|
419 |
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|
420 |
#define SIMPLE_STACK 0
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|
421 |
|
|
422 |
template<class E> inline bool GenericTaskQueue<E>::push(E t) {
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|
423 |
#if SIMPLE_STACK
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|
424 |
juint localBot = _bottom;
|
|
425 |
if (_bottom < max_elems()) {
|
|
426 |
_elems[localBot] = t;
|
|
427 |
_bottom = localBot + 1;
|
|
428 |
return true;
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|
429 |
} else {
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|
430 |
return false;
|
|
431 |
}
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|
432 |
#else
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|
433 |
juint localBot = _bottom;
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|
434 |
assert((localBot >= 0) && (localBot < n()), "_bottom out of range.");
|
|
435 |
jushort top = get_top();
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|
436 |
juint dirty_n_elems = dirty_size(localBot, top);
|
|
437 |
assert((dirty_n_elems >= 0) && (dirty_n_elems < n()),
|
|
438 |
"n_elems out of range.");
|
|
439 |
if (dirty_n_elems < max_elems()) {
|
|
440 |
_elems[localBot] = t;
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|
441 |
_bottom = increment_index(localBot);
|
|
442 |
return true;
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|
443 |
} else {
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|
444 |
return push_slow(t, dirty_n_elems);
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|
445 |
}
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|
446 |
#endif
|
|
447 |
}
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|
448 |
|
|
449 |
template<class E> inline bool GenericTaskQueue<E>::pop_local(E& t) {
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|
450 |
#if SIMPLE_STACK
|
|
451 |
juint localBot = _bottom;
|
|
452 |
assert(localBot > 0, "precondition.");
|
|
453 |
localBot--;
|
|
454 |
t = _elems[localBot];
|
|
455 |
_bottom = localBot;
|
|
456 |
return true;
|
|
457 |
#else
|
|
458 |
juint localBot = _bottom;
|
|
459 |
// This value cannot be n-1. That can only occur as a result of
|
|
460 |
// the assignment to bottom in this method. If it does, this method
|
|
461 |
// resets the size( to 0 before the next call (which is sequential,
|
|
462 |
// since this is pop_local.)
|
|
463 |
juint dirty_n_elems = dirty_size(localBot, get_top());
|
|
464 |
assert(dirty_n_elems != n() - 1, "Shouldn't be possible...");
|
|
465 |
if (dirty_n_elems == 0) return false;
|
|
466 |
localBot = decrement_index(localBot);
|
|
467 |
_bottom = localBot;
|
|
468 |
// This is necessary to prevent any read below from being reordered
|
|
469 |
// before the store just above.
|
|
470 |
OrderAccess::fence();
|
|
471 |
t = _elems[localBot];
|
|
472 |
// This is a second read of "age"; the "size()" above is the first.
|
|
473 |
// If there's still at least one element in the queue, based on the
|
|
474 |
// "_bottom" and "age" we've read, then there can be no interference with
|
|
475 |
// a "pop_global" operation, and we're done.
|
|
476 |
juint tp = get_top();
|
|
477 |
if (size(localBot, tp) > 0) {
|
|
478 |
assert(dirty_size(localBot, tp) != n() - 1,
|
|
479 |
"Shouldn't be possible...");
|
|
480 |
return true;
|
|
481 |
} else {
|
|
482 |
// Otherwise, the queue contained exactly one element; we take the slow
|
|
483 |
// path.
|
|
484 |
return pop_local_slow(localBot, get_age());
|
|
485 |
}
|
|
486 |
#endif
|
|
487 |
}
|
|
488 |
|
|
489 |
typedef oop Task;
|
|
490 |
typedef GenericTaskQueue<Task> OopTaskQueue;
|
|
491 |
typedef GenericTaskQueueSet<Task> OopTaskQueueSet;
|
|
492 |
|
|
493 |
typedef oop* StarTask;
|
|
494 |
typedef GenericTaskQueue<StarTask> OopStarTaskQueue;
|
|
495 |
typedef GenericTaskQueueSet<StarTask> OopStarTaskQueueSet;
|
|
496 |
|
|
497 |
typedef size_t ChunkTask; // index for chunk
|
|
498 |
typedef GenericTaskQueue<ChunkTask> ChunkTaskQueue;
|
|
499 |
typedef GenericTaskQueueSet<ChunkTask> ChunkTaskQueueSet;
|
|
500 |
|
|
501 |
class ChunkTaskQueueWithOverflow: public CHeapObj {
|
|
502 |
protected:
|
|
503 |
ChunkTaskQueue _chunk_queue;
|
|
504 |
GrowableArray<ChunkTask>* _overflow_stack;
|
|
505 |
|
|
506 |
public:
|
|
507 |
ChunkTaskQueueWithOverflow() : _overflow_stack(NULL) {}
|
|
508 |
// Initialize both stealable queue and overflow
|
|
509 |
void initialize();
|
|
510 |
// Save first to stealable queue and then to overflow
|
|
511 |
void save(ChunkTask t);
|
|
512 |
// Retrieve first from overflow and then from stealable queue
|
|
513 |
bool retrieve(ChunkTask& chunk_index);
|
|
514 |
// Retrieve from stealable queue
|
|
515 |
bool retrieve_from_stealable_queue(ChunkTask& chunk_index);
|
|
516 |
// Retrieve from overflow
|
|
517 |
bool retrieve_from_overflow(ChunkTask& chunk_index);
|
|
518 |
bool is_empty();
|
|
519 |
bool stealable_is_empty();
|
|
520 |
bool overflow_is_empty();
|
|
521 |
juint stealable_size() { return _chunk_queue.size(); }
|
|
522 |
ChunkTaskQueue* task_queue() { return &_chunk_queue; }
|
|
523 |
};
|
|
524 |
|
|
525 |
#define USE_ChunkTaskQueueWithOverflow
|