fifoqueue.java

一个java方面的消息订阅发送的源码

/**
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "Exolab" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Exoffice Technologies.  For written permission,
 *    please contact [e-mail].
 *
 * 4. Products derived from this Software may not be called "Exolab"
 *    nor may "Exolab" appear in their names without prior written
 *    permission of Exoffice Technologies. Exolab is a registered
 *    trademark of Exoffice Technologies.
 *
 * 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
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2000-2004 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: FifoQueue.java,v 1.1 2004/11/26 01:50:35 tanderson Exp $
 */
package org.exolab.jms.common.util;


/**
 * This is a very simple implementation of a FIFO queue. The queue only
 * holds object types, and is created with a fixed size, and will NOT grow
 * during its life. The queue is thread safe.
 *
 * <P>Items can be added or removed to and from the queue either one at a time
 * or in bulk. When the queue is full any attempt to add another object will
 * block until the queue has space for it. Any attempt to get an object
 * from an empty queue will block until at least one item has been added.
 *
 * <P>Clients can check to see if the queue is full or empty with available
 * helper methods.
 *
 * <P>When objects are added or removed from the queue, a notify all is called
 * to wake any sleeping threads waiting on a queue resource.
 *
 * @version     $Revision: 1.1 $ $Date: 2004/11/26 01:50:35 $
 * @author      <a href="mailto:[e-mail]">Jim Mourikis</a>
 */
public class FifoQueue {

    /**
     * An array is used to hold our objects, for performance.
     */
    private Object[] _queue;

    /**
     * The max number of elements the queue can hold
     */
    private final int _capacity;

    /**
     * The actual number of elements in the queue.
     */
    private int _size;

    /**
     * The start of the queue.
     */
    private int _head;

    /**
     * The end of the queue.
     */
    private int _tail;

    /**
     * The queue constructor. Can only be created with a maximum capacity.
     * An empty queue is initially created.
     *
     * @param capacity the total number of elements this queue is allowed to
     * hold
     */
    public FifoQueue(int capacity) {
        _capacity = (capacity > 0) ? capacity : 1; // at least 1
        _queue = new Object[_capacity];
        _head = 0;
        _tail = 0;
        _size = 0;
    }

    /**
     * Get the queues max capacity.
     *
     * @return the queues max capacity.
     */
    public int getCapacity() {
        return _capacity;
    }

    /**
     * Get the number of elements the queue currently holds
     *
     * @return the number of elements in the queue
     */
    public synchronized int getSize() {
        return _size;
    }

    /**
     * Determines if the queue is empty
     *
     * @return <code>true</code> if the queue is empty
     */
    public synchronized boolean isEmpty() {
        return (_size == 0);
    }

    /**
     * Determines if the queue is full
     *
     * @return <code>true</code> if the queue is full
     */
    public synchronized boolean isFull() {
        return (_size == _capacity);
    }

    /**
     * Add a new object to the head of the queue. And inform any waiting
     * threads.
     * No checks are performed for duplicates.
     * This call will block if the queue is full, until space is available.
     *
     * @param obj the new object to add to the queue.
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void add(Object obj) throws InterruptedException {
        waitWhileFull();

        _queue[_head] = obj;
        _head = (_head + 1) % _capacity;
        _size++;
        notifyAll();
    }

    /**
     * Add a new list of objects to the head of the queue. And inform any
     * waiting threads.
     * No checks are performed for duplicates.
     * This call will block if the queue is full, until space is available.
     *
     * @param list the list of objects to add to the queue.
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void add(Object[] list) throws InterruptedException {
        // todo.
        // This could be done more efficiently as an array copy, but can only
        // copy as many elements as can fit at a time.
        for (int i = 0; i < list.length; i++) {
            add(list[i]);
        }
    }

    /**
     * Remove and return the object at the end of the queue. Notify any
     * waiting threads, once an object has been removed.
     * If the queue is currently empty this call will block until
     * an item is added.
     *
     * @return the object at the end of the queue
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized Object get() throws InterruptedException {
        waitWhileEmpty();

        Object obj = _queue[_tail];

        // remove our reference.
        _queue[_tail] = null;

        _tail = (_tail + 1) % _capacity;
        _size--;
        notifyAll();
        return obj;
    }

    /**
     * Remove and return all the objects in the queue in the order they
     * were added. Notify any waiting threads, once an object has been removed.
     * If the queue is currently empty this call will block until
     * an item is added.
     *
     * <P>If the queue is empty an empty list is returned.
     *
     * @return all objects in the queue
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized Object[] getAll() throws InterruptedException {
        Object[] list = new Object[_size];

        for (int i = 0; i < list.length; i++) {
            list[i] = get();
        }
        return list;
    }

    /**
     * Wait until timeout if the queue is empty. If timteout is 0
     * this call will block until an item is inserted into the queue.
     * If there are items in the queue this call will return imediately.
     * The return value is true if there are items available in the queue
     * else false is return if the timeout was exceeded.
     *
     * <P>Note: when there are multiple threads waiting on a queue
     * there is no guarantee which one will succeed first.
     *
     * @param timeout the time to wait for in ms.
     * @return <code>true</code> if the queue is empty
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized boolean waitUntilEmpty(long timeout)
        throws InterruptedException {
        if (timeout == 0L) {
            waitUntilEmpty();
            return true;
        }

        // wait only for the specified amount of time
        long endTime = System.currentTimeMillis() + timeout;
        long remaining = timeout;

        while (!isEmpty() && (remaining > 0L)) {
            wait(remaining);
            remaining = endTime - System.currentTimeMillis();
        }
        return isEmpty();
    }

    /**
     * Wait until the queue becomes empty.
     *
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void waitUntilEmpty() throws InterruptedException {
        while (!isEmpty()) {
            wait();
        }
    }

    /**
     * Wait while the queue is empty.
     *
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void waitWhileEmpty() throws InterruptedException {
        while (isEmpty()) {
            wait();
        }
    }

    /**
     * Wait until the queue becomes full.
     *
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void waitUntilFull() throws InterruptedException {
        while (!isFull()) {
            wait();
        }
    }

    /**
     * Wait while the queue is full.
     *
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized void waitWhileFull() throws InterruptedException {
        while (isFull()) {
            wait();
        }
    }
}