blockingworkerqueue.java

实现了Jms的服务器源码,支持多种适配器,DB,FTP,支持多种数据库

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 * 5. Due credit should be given to the Exolab Project
 *    (http://www.exolab.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
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 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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 *
 * Copyright 2000 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: BlockingWorkerQueue.java,v 1.4 2003/08/07 13:33:12 tanderson Exp $
 *
 * Date         Author  Changes
 * 5/15/2001    jima    Created
 */


package org.exolab.jms.util;

import java.util.LinkedList;


/**
 * A BlockingWorkerQueue is attached to a QueueWorker. Any thread can add
 * work to the queue. The BlockingWorkerQueue, which extends Thread, blocks
 * waiting for work to arrive. When work arrives it will be dequeued and
 * passed down to the QueueWorker for processing.
 * <p>
 * The owner can use <code>close</code> to gracefully shutdown the thread.
 *
 * @version     $Revision: 1.4 $ $Date: 2003/08/07 13:33:12 $
 * @author      <a href="mailto:[e-mail]">Jim Alateras</a>
 */
public class BlockingWorkerQueue
    extends Thread {

    /**
     * This is the runnable that will perform the work
     */
    private QueueWorker _worker = null;

    /**
     * The list is used to queue work
     */
    private LinkedList _queue = new LinkedList();

    /**
     * If this is set to true then we must close the worker queue
     */
    private boolean _closed = false;


    /**
     * Construct a blocking worker queue and attahc to the specified
     * queue worker. Make the thread a deamon thread.
     *
     * @param name - the name of the thread
     * @param worker - the queue worker attached to this queue
     */
    public BlockingWorkerQueue(String name, QueueWorker worker) {
        super("BWQ:" + name);
        _worker = worker;
        this.setDaemon(true);
    }

    /**
     * Add some work to the end of the queue
     *
     * @param work - add this piece of work
     */
    public void add(Object object) {
        synchronized (_queue) {
            _queue.addLast(object);
            _queue.notifyAll();
        }
    }

    /**
     * This method is called once the thread has started. It basically loops
     * forever removing work from the queue and passing it to the runnable.
     * <p>
     * Calling <code>close</code> on this object will terminate it.
     */
    public void run() {
        while (!_closed) {
            Object work = null;

            synchronized (_queue) {
                // if there are no messages in the queue then block
                if (_queue.size() == 0) {
                    try {
                        _queue.wait();
                    } catch (InterruptedException exception) {
                        // ignore the exception;
                    }
                    continue;
                }

                // if we get this far then there is something in the queue.
                // Remove it and hand it to the worker
                work = _queue.removeFirst();
            }

            if (work != null) {
                _worker.execute(work);
            }
        }
    }

    /**
     * Return the number of entries still on the queue
     *
     * @size int
     */
    public int size() {
        return _queue.size();
    }

    /**
     * Close this worker queue
     */
    public void close() {
        _closed = true;
        interrupt();
    }

}