BlockingQueue.java Source code

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Here is the source code for BlockingQueue.java

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/**
 * The utillib library.
 * More information is available at http://www.jinchess.com/.
 * Copyright (C) 2002 Alexander Maryanovsky.
 * All rights reserved.
 *
 * The utillib library is free software; you can redistribute
 * it and/or modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The utillib library 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 Lesser
 * General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with utillib library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

import java.util.Enumeration;
import java.util.Vector;

/**
 * <P>A blocking queue, one that always "contains" elements.
 * If it is in fact empty, the pop() and peek() method will block until an
 * item is pushed.
 * <P><B>NOTE:</B> This class is thread safe.
 *
 * @author Alexander Maryanovsky.
 */

public class BlockingQueue implements Cloneable {

    /**
     * The underlying Vector this BlockingQueue is using.
     */

    private final Vector queue;

    /**
     * The lock we use to synchronize pushing.
     */

    private final Object pushLock = new String("BlockingQueue pushLock");

    /**
     * The lock we use to synchronize popping.
     */

    private final Object popLock = new String("BlockingQueue popLock");

    /**
     * Creates a new, empty BlockingQueue.
     */

    public BlockingQueue() {
        queue = new Vector();
    }

    /**
     * Pushes an element into the queue.
     */

    public void push(Object object) {
        synchronized (pushLock) {
            queue.addElement(object);
            synchronized (this) {
                notify();
            }
        }
    }

    /**
     * Pops an element from the queue. If the queue is empty, this method blocks
     * until another thread pushes an element into the queue.
     *
     * @throws InterruptedException if the invoking thread was interrupted
     * while waiting for an element to be pushed into the queue.
     */

    public Object pop() throws InterruptedException {
        return pop(0);
    }

    /**
     * Pops an element from the queue. Unlike the pop() method, this method does not block
     * for longer than the given amount of milliseconds. When the given amount of milliseconds
     * have passed, this method will throw an InterruptedException.
     */

    public Object pop(long timeout) throws InterruptedException {
        synchronized (popLock) {
            synchronized (this) {
                if (queue.isEmpty()) {
                    wait(timeout);
                    if (queue.isEmpty())
                        throw new InterruptedException("Timed out");
                }
            }
            Object val = queue.firstElement();
            queue.removeElementAt(0);
            return val;
        }
    }

    /**
     * Returns the element on top of the queue without popping it. If the queue
     * is empty, this method blocks until another thread pushes an element into
     * the queue.
     *
     * @throws InterruptedException if the invoking thread was interrupted while
     * waiting for an element to be pushed into the queue.
     */

    public Object peek() throws InterruptedException {
        return peek(0);
    }

    /**
     * Returns the element on top of the queue without popping it.
     * Unlike the peek() method, this method does not block
     * for longer than the given amount of milliseconds. When the given amount of milliseconds
     * have passed, this method will throw an InterruptedException.
     */

    public Object peek(long timeout) throws InterruptedException {
        synchronized (popLock) {
            synchronized (this) {
                if (queue.isEmpty()) {
                    wait(timeout);
                    if (queue.isEmpty())
                        throw new InterruptedException("Timed out");
                }
            }
            return queue.firstElement();
        }
    }

    /**
     * Returns true if the queue is empty (this returns the actual state of the
     * queue, meaning it may return true even though ideologically, a BlockingQueue
     * is never empty).
     */

    public boolean isEmpty() {
        return queue.isEmpty();
    }

    /**
     * Returns true if the given element is in the queue.
     */

    public boolean contains(Object element) {
        return queue.contains(element);
    }

    /**
     * Returns the size of the queue.
     */

    public int size() {
        return queue.size();
    }

    /**
     * Returns an Enumeration of the elements in this queue. The order of the
     * elements is the same as if they were popped from the queue one by one (the
     * first element is the first element that would have been popped). <br>
     * <B>IMPORTANT:</B> Modifying the queue breaks the returned Enumeration.
     */

    public Enumeration getElements() {
        return queue.elements();
    }

    /**
     * Removes all elements from this queue.
     */

    public void removeAllElements() {
        queue.removeAllElements();
    }

    /**
     * Removes all elements from this queue.
     */

    public void clear() {
        queue.removeAllElements();
    }

    /**
     * Returns a shallow copy of this BlockingQueue.
     */

    public synchronized Object clone() {
        BlockingQueue copy = new BlockingQueue();
        Enumeration elems = getElements();
        while (elems.hasMoreElements()) {
            Object item = elems.nextElement();
            copy.push(item);
        }
        return copy;
    }

}