0N/A/*
2362N/A * Copyright (c) 1997, 2005, Oracle and/or its affiliates. All rights reserved.
0N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
0N/A *
0N/A * This code is free software; you can redistribute it and/or modify it
0N/A * under the terms of the GNU General Public License version 2 only, as
2362N/A * published by the Free Software Foundation. Oracle designates this
0N/A * particular file as subject to the "Classpath" exception as provided
2362N/A * by Oracle in the LICENSE file that accompanied this code.
0N/A *
0N/A * This code is distributed in the hope that it will be useful, but WITHOUT
0N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
0N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
0N/A * version 2 for more details (a copy is included in the LICENSE file that
0N/A * accompanied this code).
0N/A *
0N/A * You should have received a copy of the GNU General Public License version
0N/A * 2 along with this work; if not, write to the Free Software Foundation,
0N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
0N/A *
2362N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
2362N/A * or visit www.oracle.com if you need additional information or have any
2362N/A * questions.
0N/A */
0N/A
0N/Apackage java.lang.ref;
0N/A
0N/A/**
0N/A * Reference queues, to which registered reference objects are appended by the
0N/A * garbage collector after the appropriate reachability changes are detected.
0N/A *
0N/A * @author Mark Reinhold
0N/A * @since 1.2
0N/A */
0N/A
0N/Apublic class ReferenceQueue<T> {
0N/A
0N/A /**
0N/A * Constructs a new reference-object queue.
0N/A */
0N/A public ReferenceQueue() { }
0N/A
0N/A private static class Null extends ReferenceQueue {
0N/A boolean enqueue(Reference r) {
0N/A return false;
0N/A }
0N/A }
0N/A
0N/A static ReferenceQueue NULL = new Null();
0N/A static ReferenceQueue ENQUEUED = new Null();
0N/A
0N/A static private class Lock { };
0N/A private Lock lock = new Lock();
1036N/A private volatile Reference<? extends T> head = null;
0N/A private long queueLength = 0;
0N/A
0N/A boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
0N/A synchronized (r) {
0N/A if (r.queue == ENQUEUED) return false;
0N/A synchronized (lock) {
0N/A r.queue = ENQUEUED;
0N/A r.next = (head == null) ? r : head;
0N/A head = r;
0N/A queueLength++;
0N/A if (r instanceof FinalReference) {
0N/A sun.misc.VM.addFinalRefCount(1);
0N/A }
0N/A lock.notifyAll();
0N/A return true;
0N/A }
0N/A }
0N/A }
0N/A
0N/A private Reference<? extends T> reallyPoll() { /* Must hold lock */
0N/A if (head != null) {
0N/A Reference<? extends T> r = head;
0N/A head = (r.next == r) ? null : r.next;
0N/A r.queue = NULL;
0N/A r.next = r;
0N/A queueLength--;
0N/A if (r instanceof FinalReference) {
0N/A sun.misc.VM.addFinalRefCount(-1);
0N/A }
0N/A return r;
0N/A }
0N/A return null;
0N/A }
0N/A
0N/A /**
0N/A * Polls this queue to see if a reference object is available. If one is
0N/A * available without further delay then it is removed from the queue and
0N/A * returned. Otherwise this method immediately returns <tt>null</tt>.
0N/A *
0N/A * @return A reference object, if one was immediately available,
0N/A * otherwise <code>null</code>
0N/A */
0N/A public Reference<? extends T> poll() {
1036N/A if (head == null)
1036N/A return null;
0N/A synchronized (lock) {
0N/A return reallyPoll();
0N/A }
0N/A }
0N/A
0N/A /**
0N/A * Removes the next reference object in this queue, blocking until either
0N/A * one becomes available or the given timeout period expires.
0N/A *
0N/A * <p> This method does not offer real-time guarantees: It schedules the
0N/A * timeout as if by invoking the {@link Object#wait(long)} method.
0N/A *
0N/A * @param timeout If positive, block for up to <code>timeout</code>
0N/A * milliseconds while waiting for a reference to be
0N/A * added to this queue. If zero, block indefinitely.
0N/A *
0N/A * @return A reference object, if one was available within the specified
0N/A * timeout period, otherwise <code>null</code>
0N/A *
0N/A * @throws IllegalArgumentException
0N/A * If the value of the timeout argument is negative
0N/A *
0N/A * @throws InterruptedException
0N/A * If the timeout wait is interrupted
0N/A */
0N/A public Reference<? extends T> remove(long timeout)
0N/A throws IllegalArgumentException, InterruptedException
0N/A {
0N/A if (timeout < 0) {
0N/A throw new IllegalArgumentException("Negative timeout value");
0N/A }
0N/A synchronized (lock) {
0N/A Reference<? extends T> r = reallyPoll();
0N/A if (r != null) return r;
0N/A for (;;) {
0N/A lock.wait(timeout);
0N/A r = reallyPoll();
0N/A if (r != null) return r;
0N/A if (timeout != 0) return null;
0N/A }
0N/A }
0N/A }
0N/A
0N/A /**
0N/A * Removes the next reference object in this queue, blocking until one
0N/A * becomes available.
0N/A *
0N/A * @return A reference object, blocking until one becomes available
0N/A * @throws InterruptedException If the wait is interrupted
0N/A */
0N/A public Reference<? extends T> remove() throws InterruptedException {
0N/A return remove(0);
0N/A }
0N/A
0N/A}