/*
 * Copyright (c) 2003-2007 Sun Microsystems, Inc.  All rights reserved.
 *  
 *  The Sun Project JXTA(TM) Software License
 *  
 *  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 Sun Microsystems, Inc. for JXTA(TM) technology." 
 *     Alternately, this acknowledgment may appear in the software itself, if 
 *     and wherever such third-party acknowledgments normally appear.
 *  
 *  4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must 
 *     not be used to endorse or promote products derived from this software 
 *     without prior written permission. For written permission, please contact 
 *     Project JXTA at http://www.jxta.org.
 *  
 *  5. Products derived from this software may not be called "JXTA", nor may 
 *     "JXTA" appear in their name, without prior written permission of Sun.
 *  
 *  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 SUN 
 *  MICROSYSTEMS 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.
 *  
 *  JXTA is a registered trademark of Sun Microsystems, Inc. in the United 
 *  States and other countries.
 *  
 *  Please see the license information page at :
 *  <http://www.jxta.org/project/www/license.html> for instructions on use of 
 *  the license in source files.
 *  
 *  ====================================================================
 *  
 *  This software consists of voluntary contributions made by many individuals 
 *  on behalf of Project JXTA. For more information on Project JXTA, please see 
 *  http://www.jxta.org.
 *  
 *  This license is based on the BSD license adopted by the Apache Foundation. 
 */

package net.jxta.impl.util.pipe.reliable;


/**
 * A basis for any flow control module to be plugged into
 * ReliableOutputStream.  Synchronization can is assumed to be
 * provided externaly. However all implementations are required to
 * allow the getRwindow() method to be called at any time without
 * synchronization.
 */

public abstract class FlowControl {

    /**
     * Returns the rwindow size that this flow control module suggests to use
     * at this point in time.
     * @return the remote window size
     */
    public abstract int getRwindow();

    /**
     * Indicates that a new ack message is being processed.
     */
    public void ackEventBegin() {}

    /**
     * Invoked for each packet that is believed to have been received
     * per the current ack message.
     *
     * @param seqnum The sequence number of the received packet.
     */
    public void packetACKed(int seqnum) {}

    /**
     * Invoked for each packet that is believed to have been lost
     * per the current ack message.
     *
     * @param seqnum The sequence number of the missing packet.
     */
    public void packetMissing(int seqnum) {}

    /**
     * Concludes rwindow update for this ackEvent. That's where all the
     * smarts are. A number of externally computed parameters must be
     * passed.
     *
     * @param rQSize the last known value of the remote queue size.
     * @param aveRTT the latest estimate of the average RTT.
     * @param lastRTT the RTT inferred from the most recent ACK message.
     * @return int the new recommended value for rwindow.
     */

    public abstract int ackEventEnd(int rQSize, long aveRTT, long lastRTT);
}