LinkedQueue.java revision 2362
* Copyright (c) 1999, Oracle and/or its affiliates. All rights reserved. * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * - Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * - Neither the name of Oracle nor the names of its * contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Originally written by Doug Lea and released into the public domain. This may be used for any purposes whatsoever without acknowledgment. Thanks for the assistance and support of Sun Microsystems Labs, and everyone contributing, testing, and using this code. 11Jun1998 dl Create public version 10dec1998 dl added isEmpty 10jun1999 bc modified for isolated use // Original was in package EDU.oswego.cs.dl.util.concurrent; * A linked list based channel implementation, * adapted from the TwoLockQueue class from CPJ. * The algorithm avoids contention between puts * and takes when the queue is not empty. * Normally a put and a take can proceed simultaneously. * (Although it does not allow multiple concurrent puts or takes.) * This class tends to perform more efficently than * Dummy header node of list. The first actual node, if it exists, is always * at head_.next. After each take, the old first node becomes the head. * Helper monitor for managing access to last node, in case it is also first. * last_ and waitingForTake_ ONLY used with synch on appendMonitor_ * The last node of list. Put() appends to list, so modifies last_ * The number of threads waiting for a take. * Notifications are provided in put only if greater than zero. * The bookkeeping is worth it here since in reasonably balanced * usages, the notifications will hardly ever be necessary, so * the call overhead to notify can be eliminated. // try to extract. If fail, then enter wait-based retry loop public synchronized boolean isEmpty() {