//******************************************************************************
//
// File:    Channel.java
// Package: edu.rit.mp
// Unit:    Class edu.rit.mp.Channel
//
// This Java source file is copyright (C) 2008 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// Linking this library statically or dynamically with other modules is making a
// combined work based on this library. Thus, the terms and conditions of the
// GNU General Public License cover the whole combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent modules, and
// to copy and distribute the resulting executable under terms of your choice,
// provided that you also meet, for each linked independent module, the terms
// and conditions of the license of that module. An independent module is a
// module which is not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the library, but
// you are not obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.mp;

import java.io.IOException;
import java.io.PrintStream;

import java.net.InetSocketAddress;

/**
 * Class Channel provides a channel for sending and receiving messages in the
 * Message Protocol (MP).
 * <P>
 * A channel object is not constructed directly. Rather, a channel group object
 * is used to connect a channel to another computer, accept a channel connection
 * from another computer, or obtain a "loopback" channel within the same
 * computer. See class {@linkplain ChannelGroup} for further information.
 * <P>
 * An information object may be associated with a channel. An application using
 * MP can use the information object to hold additional data about the channel.
 *
 * @author  Alan Kaminsky
 * @version 13-May-2008
 */
public abstract class Channel
	{

// Hidden data members.

	ChannelGroup myChannelGroup;
	IORequestList myIORequestList;
	Object myInfo;

	int myWriteState = WRITE_OPEN;
		static final int WRITE_OPEN   = 0;
		static final int WRITE_CLOSED = 1;

	int myReadState = READ_OPEN;
		static final int READ_OPEN   = 0;
		static final int READ_CLOSED = 1;

// Hidden constructors.

	/**
	 * Construct a new channel.
	 *
	 * @param  theChannelGroup  Enclosing channel group.
	 */
	Channel
		(ChannelGroup theChannelGroup)
		{
		myChannelGroup = theChannelGroup;
		myIORequestList = theChannelGroup.myIORequestList;
		}

// Exported operations.

	/**
	 * Obtain the channel group that created this channel.
	 *
	 * @return  Channel group.
	 */
	public ChannelGroup getChannelGroup()
		{
		return myChannelGroup;
		}

	/**
	 * Obtain the channel group ID of this channel's near end channel group.
	 *
	 * @return  Near end channel group ID.
	 */
	public abstract int nearEndChannelGroupId();

	/**
	 * Obtain the channel group ID of this channel's far end channel group.
	 *
	 * @return  Far end channel group ID.
	 */
	public abstract int farEndChannelGroupId();

	/**
	 * Obtain this channel's near end address. This is the host and port of the
	 * near end of this channel's connection.
	 *
	 * @return  Near end address.
	 */
	public abstract InetSocketAddress nearEndAddress();

	/**
	 * Obtain this channel's far end address. This is the host and port of the
	 * far end of this channel's connection.
	 *
	 * @return  Far end address.
	 */
	public abstract InetSocketAddress farEndAddress();

	/**
	 * Obtain this channel's information object.
	 *
	 * @return  Information object, or null if none.
	 */
	public Object info()
		{
		return myInfo;
		}

	/**
	 * Set this channel's information object.
	 *
	 * @param  theInfo  Information object, or null if none.
	 */
	public void info
		(Object theInfo)
		{
		myInfo = theInfo;
		}

	/**
	 * Close this channel. Any pending send requests will fail with a
	 * {@linkplain ChannelClosedException}.
	 */
	public void close()
		{
		// To avoid deadlock, synchronize first on the channel group, then on
		// this channel.
		synchronized (myChannelGroup)
			{
			synchronized (this)
				{
				myChannelGroup.removeChannel (this);
				myWriteState = WRITE_CLOSED;
				myReadState = READ_CLOSED;
				subclassClose();
				}
			}
		}

	/**
	 * Finalize this channel.
	 */
	protected void finalize()
		{
		close();
		}

	/**
	 * Returns a string version of this channel.
	 */
	public String toString()
		{
		return
			getClass().getName() +
			"(near=" + nearEndAddress() +
			",far=" + farEndAddress() + ")";
		}

	/**
	 * Dump the state of this channel on the given print stream. For debugging.
	 *
	 * @param  out     Print stream.
	 * @param  prefix  String to print at the beginning of each line.
	 */
	public void dump
		(PrintStream out,
		 String prefix)
		{
		out.println (prefix+getClass().getName()+"@"+Integer.toHexString(System.identityHashCode(this)));
		out.println (prefix+"myChannelGroup = "+myChannelGroup);
		out.println (prefix+"myIORequestList = "+myIORequestList);
		out.println (prefix+"myInfo = "+myInfo);
		out.println (prefix+"myWriteState = "+(myWriteState==WRITE_OPEN?"WRITE_OPEN":"WRITE_CLOSED"));
		out.println (prefix+"myReadState = "+(myReadState==READ_OPEN?"READ_OPEN":"READ_CLOSED"));
		out.println (prefix+"nearEndChannelGroupId() = "+nearEndChannelGroupId());
		out.println (prefix+"farEndChannelGroupId() = "+farEndChannelGroupId());
		out.println (prefix+"nearEndAddress() = "+nearEndAddress());
		out.println (prefix+"farEndAddress() = "+farEndAddress());
		}

// Hidden operations.

	/**
	 * Start sending and receiving messages via this channel.
	 */
	void start()
		{
		}

	/**
	 * Send a message via this channel. The I/O request object must be newly
	 * constructed with the message tag and source buffer fields filled in. This
	 * method is allowed to return immediately and let the message be sent in a
	 * separate thread. The calling thread should use the I/O request object to
	 * wait for the message send to complete.
	 *
	 * @param  theIORequest  I/O request object.
	 *
	 * @exception  IOException
	 *     Thrown if an I/O error occurred.
	 */
	abstract void send
		(IORequest theIORequest)
		throws IOException;

	/**
	 * Perform additional close actions in a subclass.
	 */
	void subclassClose()
		{
		}

	}