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/*
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* Copyright (c) 1996, 2005, Oracle and/or its affiliates. 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. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package sun.misc;
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import java.util.Enumeration;
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import java.util.NoSuchElementException;
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/**
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* Queue: implements a simple queue mechanism. Allows for enumeration of the
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* elements.
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*
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* @author Herb Jellinek
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*/
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public class Queue {
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int length = 0;
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QueueElement head = null;
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QueueElement tail = null;
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public Queue() {
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}
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/**
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* Enqueue an object.
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*/
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public synchronized void enqueue(Object obj) {
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QueueElement newElt = new QueueElement(obj);
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if (head == null) {
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head = newElt;
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tail = newElt;
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length = 1;
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} else {
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newElt.next = head;
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head.prev = newElt;
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head = newElt;
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length++;
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}
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notify();
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}
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/**
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* Dequeue the oldest object on the queue. Will wait indefinitely.
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*
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* @return the oldest object on the queue.
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* @exception java.lang.InterruptedException if any thread has
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* interrupted this thread.
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*/
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public Object dequeue() throws InterruptedException {
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return dequeue(0L);
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}
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/**
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* Dequeue the oldest object on the queue.
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* @param timeOut the number of milliseconds to wait for something
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* to arrive.
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*
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* @return the oldest object on the queue.
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* @exception java.lang.InterruptedException if any thread has
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* interrupted this thread.
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*/
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public synchronized Object dequeue(long timeOut)
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throws InterruptedException {
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while (tail == null) {
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wait(timeOut);
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}
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QueueElement elt = tail;
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tail = elt.prev;
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if (tail == null) {
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head = null;
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} else {
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tail.next = null;
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}
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length--;
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return elt.obj;
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}
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/**
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* Is the queue empty?
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* @return true if the queue is empty.
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*/
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public synchronized boolean isEmpty() {
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return (tail == null);
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}
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/**
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* Returns an enumeration of the elements in Last-In, First-Out
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* order. Use the Enumeration methods on the returned object to
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* fetch the elements sequentially.
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*/
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public final synchronized Enumeration elements() {
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return new LIFOQueueEnumerator(this);
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}
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/**
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* Returns an enumeration of the elements in First-In, First-Out
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* order. Use the Enumeration methods on the returned object to
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* fetch the elements sequentially.
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*/
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public final synchronized Enumeration reverseElements() {
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return new FIFOQueueEnumerator(this);
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}
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public synchronized void dump(String msg) {
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System.err.println(">> "+msg);
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System.err.println("["+length+" elt(s); head = "+
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(head == null ? "null" : (head.obj)+"")+
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" tail = "+(tail == null ? "null" : (tail.obj)+""));
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QueueElement cursor = head;
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QueueElement last = null;
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while (cursor != null) {
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System.err.println(" "+cursor);
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last = cursor;
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cursor = cursor.next;
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}
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if (last != tail) {
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System.err.println(" tail != last: "+tail+", "+last);
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}
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System.err.println("]");
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}
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}
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final class FIFOQueueEnumerator implements Enumeration {
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Queue queue;
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QueueElement cursor;
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FIFOQueueEnumerator(Queue q) {
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queue = q;
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cursor = q.tail;
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}
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public boolean hasMoreElements() {
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return (cursor != null);
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}
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public Object nextElement() {
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synchronized (queue) {
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if (cursor != null) {
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QueueElement result = cursor;
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cursor = cursor.prev;
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return result.obj;
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}
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}
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throw new NoSuchElementException("FIFOQueueEnumerator");
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}
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}
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final class LIFOQueueEnumerator implements Enumeration {
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Queue queue;
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QueueElement cursor;
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LIFOQueueEnumerator(Queue q) {
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queue = q;
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cursor = q.head;
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}
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public boolean hasMoreElements() {
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return (cursor != null);
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}
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public Object nextElement() {
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synchronized (queue) {
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if (cursor != null) {
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QueueElement result = cursor;
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cursor = cursor.next;
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return result.obj;
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}
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}
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throw new NoSuchElementException("LIFOQueueEnumerator");
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}
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}
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class QueueElement {
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QueueElement next = null;
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QueueElement prev = null;
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Object obj = null;
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QueueElement(Object obj) {
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this.obj = obj;
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}
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public String toString() {
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return "QueueElement[obj="+obj+(prev == null ? " null" : " prev")+
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(next == null ? " null" : " next")+"]";
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}
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}
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