messagequeue.java

stun的java实现

/*
 * Stun4j, the OpenSource Java Solution for NAT and Firewall Traversal.
 *
 * Distributable under LGPL license.
 * See terms of license at gnu.org.
 */
package net.java.stun4j.stack;

import java.util.*;

/**
 * The class is used as a part of the stack's thread pooling strategy. Method
 * access is synchronized and message delivery ( remove() ) is blocking in the
 * case of an empty queue.
 *
 * <p>Organisation: Louis Pasteur University, Strasbourg, France</p>
 * <p>Network Research Team (http://www-r2.u-strasbg.fr)</p></p>
 *
 * @author Emil Ivov
 * @version 0.1
 */
class MessageQueue
{
    // not sure whether Vector is the best choice here since we explicitly
    //sync all methods ... review later
    private Vector queue = new Vector();

    //keep a copy of the fifo size and make it accessible for concurrent queries.
    private int    size  = 0;

    /**
     * Create an empty MessaeFIFO
     */
    MessageQueue()
    {

    }

    /**
     * Returns the number of messages currently in the queue.
     * @return the number of messages in the queue.
     */
    public int getSize()
    {
        return size;
    }

    /**
     * Determines whether the FIFO is currently empty.
     * @return true if the FIFO is currently empty and false otherwise.
     */
    public boolean isEmpty()
    {
        return (size == 0);
    }

    /**
     * Adds the specified message to the queue.
     *
     * @param rawMessage the message to add.
     */
    public synchronized void add(RawMessage rawMessage)
    {
        queue.add(rawMessage);
        size++;

        notifyAll();
    }

    /**
     * Removes and returns the oldest message from the fifo. If there are
     * currently no messages in the queue the method block until there is at
     * least one message.
     *
     *
     * @return the oldest message in the fifo.
     * @throws java.lang.InterruptedException if an InterruptedException is thrown
     * wail waiting for a new message to be added.
     */
    public synchronized RawMessage remove()
        throws InterruptedException
    {
        waitWhileEmpty();
        RawMessage rawMessage = (RawMessage)queue.remove(0);

        size--;
        return rawMessage;
    }

    /**
     * Blocks until there is at least one message in the queue.
     *
     * @throws java.lang.InterruptedException if an InterruptedException is thrown
     * wail waiting for a new message to be added.
     */
    public synchronized void waitWhileEmpty() throws InterruptedException
    {
        while (isEmpty())
        {
            wait();
        }
    }

}