1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/rt/emul/compact/src/main/java/java/lang/ref/ReferenceQueue.java Tue Feb 26 16:54:16 2013 +0100
1.3 @@ -0,0 +1,148 @@
1.4 +/*
1.5 + * Copyright (c) 1997, 2005, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation. Oracle designates this
1.11 + * particular file as subject to the "Classpath" exception as provided
1.12 + * by Oracle in the LICENSE file that accompanied this code.
1.13 + *
1.14 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 + * version 2 for more details (a copy is included in the LICENSE file that
1.18 + * accompanied this code).
1.19 + *
1.20 + * You should have received a copy of the GNU General Public License version
1.21 + * 2 along with this work; if not, write to the Free Software Foundation,
1.22 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 + *
1.24 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 + * or visit www.oracle.com if you need additional information or have any
1.26 + * questions.
1.27 + */
1.28 +
1.29 +package java.lang.ref;
1.30 +
1.31 +/**
1.32 + * Reference queues, to which registered reference objects are appended by the
1.33 + * garbage collector after the appropriate reachability changes are detected.
1.34 + *
1.35 + * @author Mark Reinhold
1.36 + * @since 1.2
1.37 + */
1.38 +
1.39 +public class ReferenceQueue<T> {
1.40 +
1.41 + /**
1.42 + * Constructs a new reference-object queue.
1.43 + */
1.44 + public ReferenceQueue() { }
1.45 +
1.46 + private static class Null extends ReferenceQueue {
1.47 + boolean enqueue(Reference r) {
1.48 + return false;
1.49 + }
1.50 + }
1.51 +
1.52 + static ReferenceQueue NULL = new Null();
1.53 + static ReferenceQueue ENQUEUED = new Null();
1.54 +
1.55 + static private class Lock { };
1.56 + private Lock lock = new Lock();
1.57 + private volatile Reference<? extends T> head = null;
1.58 + private long queueLength = 0;
1.59 +
1.60 + boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
1.61 + synchronized (r) {
1.62 + if (r.queue == ENQUEUED) return false;
1.63 + synchronized (lock) {
1.64 + r.queue = ENQUEUED;
1.65 + r.next = (head == null) ? r : head;
1.66 + head = r;
1.67 + queueLength++;
1.68 + lock.notifyAll();
1.69 + return true;
1.70 + }
1.71 + }
1.72 + }
1.73 +
1.74 + private Reference<? extends T> reallyPoll() { /* Must hold lock */
1.75 + if (head != null) {
1.76 + Reference<? extends T> r = head;
1.77 + head = (r.next == r) ? null : r.next;
1.78 + r.queue = NULL;
1.79 + r.next = r;
1.80 + queueLength--;
1.81 + return r;
1.82 + }
1.83 + return null;
1.84 + }
1.85 +
1.86 + /**
1.87 + * Polls this queue to see if a reference object is available. If one is
1.88 + * available without further delay then it is removed from the queue and
1.89 + * returned. Otherwise this method immediately returns <tt>null</tt>.
1.90 + *
1.91 + * @return A reference object, if one was immediately available,
1.92 + * otherwise <code>null</code>
1.93 + */
1.94 + public Reference<? extends T> poll() {
1.95 + if (head == null)
1.96 + return null;
1.97 + synchronized (lock) {
1.98 + return reallyPoll();
1.99 + }
1.100 + }
1.101 +
1.102 + /**
1.103 + * Removes the next reference object in this queue, blocking until either
1.104 + * one becomes available or the given timeout period expires.
1.105 + *
1.106 + * <p> This method does not offer real-time guarantees: It schedules the
1.107 + * timeout as if by invoking the {@link Object#wait(long)} method.
1.108 + *
1.109 + * @param timeout If positive, block for up to <code>timeout</code>
1.110 + * milliseconds while waiting for a reference to be
1.111 + * added to this queue. If zero, block indefinitely.
1.112 + *
1.113 + * @return A reference object, if one was available within the specified
1.114 + * timeout period, otherwise <code>null</code>
1.115 + *
1.116 + * @throws IllegalArgumentException
1.117 + * If the value of the timeout argument is negative
1.118 + *
1.119 + * @throws InterruptedException
1.120 + * If the timeout wait is interrupted
1.121 + */
1.122 + public Reference<? extends T> remove(long timeout)
1.123 + throws IllegalArgumentException, InterruptedException
1.124 + {
1.125 + if (timeout < 0) {
1.126 + throw new IllegalArgumentException("Negative timeout value");
1.127 + }
1.128 + synchronized (lock) {
1.129 + Reference<? extends T> r = reallyPoll();
1.130 + if (r != null) return r;
1.131 + for (;;) {
1.132 + lock.wait(timeout);
1.133 + r = reallyPoll();
1.134 + if (r != null) return r;
1.135 + if (timeout != 0) return null;
1.136 + }
1.137 + }
1.138 + }
1.139 +
1.140 + /**
1.141 + * Removes the next reference object in this queue, blocking until one
1.142 + * becomes available.
1.143 + *
1.144 + * @return A reference object, blocking until one becomes available
1.145 + * @throws InterruptedException If the wait is interrupted
1.146 + */
1.147 + public Reference<? extends T> remove() throws InterruptedException {
1.148 + return remove(0);
1.149 + }
1.150 +
1.151 +}