| /* |
| * Copyright (c) 1996, 2005, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package sun.misc; |
| |
| import java.util.Enumeration; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * Queue: implements a simple queue mechanism. Allows for enumeration of the |
| * elements. |
| * |
| * @author Herb Jellinek |
| */ |
| |
| public class Queue { |
| |
| int length = 0; |
| |
| QueueElement head = null; |
| QueueElement tail = null; |
| |
| public Queue() { |
| } |
| |
| /** |
| * Enqueue an object. |
| */ |
| public synchronized void enqueue(Object obj) { |
| |
| QueueElement newElt = new QueueElement(obj); |
| |
| if (head == null) { |
| head = newElt; |
| tail = newElt; |
| length = 1; |
| } else { |
| newElt.next = head; |
| head.prev = newElt; |
| head = newElt; |
| length++; |
| } |
| notify(); |
| } |
| |
| /** |
| * Dequeue the oldest object on the queue. Will wait indefinitely. |
| * |
| * @return the oldest object on the queue. |
| * @exception java.lang.InterruptedException if any thread has |
| * interrupted this thread. |
| */ |
| public Object dequeue() throws InterruptedException { |
| return dequeue(0L); |
| } |
| |
| /** |
| * Dequeue the oldest object on the queue. |
| * @param timeOut the number of milliseconds to wait for something |
| * to arrive. |
| * |
| * @return the oldest object on the queue. |
| * @exception java.lang.InterruptedException if any thread has |
| * interrupted this thread. |
| */ |
| public synchronized Object dequeue(long timeOut) |
| throws InterruptedException { |
| |
| while (tail == null) { |
| wait(timeOut); |
| } |
| QueueElement elt = tail; |
| tail = elt.prev; |
| if (tail == null) { |
| head = null; |
| } else { |
| tail.next = null; |
| } |
| length--; |
| return elt.obj; |
| } |
| |
| /** |
| * Is the queue empty? |
| * @return true if the queue is empty. |
| */ |
| public synchronized boolean isEmpty() { |
| return (tail == null); |
| } |
| |
| /** |
| * Returns an enumeration of the elements in Last-In, First-Out |
| * order. Use the Enumeration methods on the returned object to |
| * fetch the elements sequentially. |
| */ |
| public final synchronized Enumeration elements() { |
| return new LIFOQueueEnumerator(this); |
| } |
| |
| /** |
| * Returns an enumeration of the elements in First-In, First-Out |
| * order. Use the Enumeration methods on the returned object to |
| * fetch the elements sequentially. |
| */ |
| public final synchronized Enumeration reverseElements() { |
| return new FIFOQueueEnumerator(this); |
| } |
| |
| public synchronized void dump(String msg) { |
| System.err.println(">> "+msg); |
| System.err.println("["+length+" elt(s); head = "+ |
| (head == null ? "null" : (head.obj)+"")+ |
| " tail = "+(tail == null ? "null" : (tail.obj)+"")); |
| QueueElement cursor = head; |
| QueueElement last = null; |
| while (cursor != null) { |
| System.err.println(" "+cursor); |
| last = cursor; |
| cursor = cursor.next; |
| } |
| if (last != tail) { |
| System.err.println(" tail != last: "+tail+", "+last); |
| } |
| System.err.println("]"); |
| } |
| } |
| |
| final class FIFOQueueEnumerator implements Enumeration { |
| Queue queue; |
| QueueElement cursor; |
| |
| FIFOQueueEnumerator(Queue q) { |
| queue = q; |
| cursor = q.tail; |
| } |
| |
| public boolean hasMoreElements() { |
| return (cursor != null); |
| } |
| |
| public Object nextElement() { |
| synchronized (queue) { |
| if (cursor != null) { |
| QueueElement result = cursor; |
| cursor = cursor.prev; |
| return result.obj; |
| } |
| } |
| throw new NoSuchElementException("FIFOQueueEnumerator"); |
| } |
| } |
| |
| final class LIFOQueueEnumerator implements Enumeration { |
| Queue queue; |
| QueueElement cursor; |
| |
| LIFOQueueEnumerator(Queue q) { |
| queue = q; |
| cursor = q.head; |
| } |
| |
| public boolean hasMoreElements() { |
| return (cursor != null); |
| } |
| |
| public Object nextElement() { |
| synchronized (queue) { |
| if (cursor != null) { |
| QueueElement result = cursor; |
| cursor = cursor.next; |
| return result.obj; |
| } |
| } |
| throw new NoSuchElementException("LIFOQueueEnumerator"); |
| } |
| } |
| |
| class QueueElement { |
| QueueElement next = null; |
| QueueElement prev = null; |
| |
| Object obj = null; |
| |
| QueueElement(Object obj) { |
| this.obj = obj; |
| } |
| |
| public String toString() { |
| return "QueueElement[obj="+obj+(prev == null ? " null" : " prev")+ |
| (next == null ? " null" : " next")+"]"; |
| } |
| } |