Smack/source/org/jivesoftware/smack/PacketCollector.java

/**
 * $RCSfile$
 * $Revision$
 * $Date$
 *
 * Copyright (C) 2002-2003 Jive Software. All rights reserved.
 * ====================================================================
 * The Jive Software License (based on Apache Software License, Version 1.1)
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 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 end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by
 *        Jive Software (http://www.jivesoftware.com)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Smack" and "Jive Software" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please
 *    contact webmaster@jivesoftware.com.
 *
 * 5. Products derived from this software may not be called "Smack",
 *    nor may "Smack" appear in their name, without prior written
 *    permission of Jive Software.
 *
 * THIS SOFTWARE IS PROVIDED ``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 JIVE SOFTWARE OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 */

package org.jivesoftware.smack;

import org.jivesoftware.smack.packet.Packet;
import org.jivesoftware.smack.filter.PacketFilter;

import java.util.LinkedList;

/**
 * Provides a mechanism to collect packets into a result queue that pass a
 * specified filter. The collector lets you perform blocking and polling
 * operations on the result queue. So, a PacketCollector is more suitable to
 * use than a {@link PacketListener} when you need to wait for a specific
 * result.<p>
 *
 * Each packet collector will queue up to 2^16 packets for processing before
 * older packets are automatically dropped.
 *
 * @see XMPPConnection#createPacketCollector(PacketFilter)
 * @author Matt Tucker
 */
public class PacketCollector {

    /**
     * Max number of packets that any one collector can hold. After the max is
     * reached, older packets will be automatically dropped from the queue as
     * new packets are added.
     */
    private static final int MAX_PACKETS = 65536;

    private PacketFilter packetFilter;
    private LinkedList resultQueue;
    private PacketReader packetReader;
    private boolean cancelled = false;

    /**
     * Creates a new packet collector. If the packet filter is <tt>null</tt>, then
     * all packets will match this collector.
     *
     * @param packetReader the packetReader the collector is tied to.
     * @param packetFilter determines which packets will be returned by this collector.
     */
    protected PacketCollector(PacketReader packetReader, PacketFilter packetFilter) {
        this.packetReader = packetReader;
        this.packetFilter = packetFilter;
        this.resultQueue = new LinkedList();
         // Add the collector to the packet reader's list of active collector.
        synchronized (packetReader.collectors) {
            packetReader.collectors.add(this);
        }
    }

    /**
     * Explicitly cancels the packet collector so that no more results are
     * queued up. Once a packet collector has been cancelled, it cannot be
     * re-enabled. Instead, a new packet collector must be created.
     */
    public void cancel() {
        // If the packet collector has already been cancelled, do nothing.
        if (cancelled) {
            return;
        }
        else {
            cancelled = true;
            // Remove object from collectors list by setting the value in the
            // list at the correct index to null. The collector thread will
            // automatically remove the actual list entry when it can.
            synchronized (packetReader.collectors) {
                int index = packetReader.collectors.indexOf(this);
                packetReader.collectors.set(index, null);
            }
        }
    }

    /**
     * Returns the packet filter associated with this packet collector. The packet
     * filter is used to determine what packets are queued as results.
     *
     * @return the packet filter.
     */
    public PacketFilter getPacketFilter() {
        return packetFilter;
    }

    /**
     * Polls to see if a packet is currently available and returns it, or
     * immediately returns <tt>null</tt> if no packets are currently in the
     * result queue.
     *
     * @return the next packet result, or <tt>null</tt> if there are no more
     *      results.
     */
    public synchronized Packet pollResult() {
        if (resultQueue.isEmpty()) {
            return null;
        }
        else {
            return (Packet)resultQueue.removeLast();
        }
    }

    /**
     * Returns the next available packet. The method call will block (not return)
     * until a packet is available.
     *
     * @return the next available packet.
     */
    public synchronized Packet nextResult() {
        // Wait indefinitely until there is a result to return.
        while (resultQueue.isEmpty()) {
            try {
                wait();
            }
            catch (InterruptedException ie) { }
        }
        return (Packet)resultQueue.removeLast();
    }

    /**
     * Returns the next available packet. The method call will block (not return)
     * until a packet is available or the <tt>timeout</tt> has elapased. If the
     * timeout elapses without a result, <tt>null</tt> will be returned.
     *
     * @param timeout the amount of time to wait for the next packet (in milleseconds).
     * @return the next available packet.
     */
    public synchronized Packet nextResult(long timeout) {
        // Wait up to the specified amount of time for a result.
        if (resultQueue.isEmpty()) {
            try {
                wait(timeout);
            }
            catch (InterruptedException ie) { }
        }
        // If still no result, return null.
        if (resultQueue.isEmpty()) {
            return null;
        }
        else {
            return (Packet)resultQueue.removeLast();
        }
    }

    /**
     * Processes a packet to see if it meets the criteria for this packet collector.
     * If so, the packet is added to the result queue.
     *
     * @param packet the packet to process.
     */
    protected synchronized void processPacket(Packet packet) {
        if (packet == null) {
            return;
        }
        if (packetFilter == null || packetFilter.accept(packet)) {
            // If the max number of packets has been reached, remove the oldest one.
            if (resultQueue.size() == MAX_PACKETS) {
                resultQueue.removeLast();
            }
            // Add the new packet.
            resultQueue.addFirst(packet);
            // Notify waiting threads a result is available.
            notifyAll();
        }
    }
}