//******************************************************************************
//
// File:    CommRequest.java
// Package: edu.rit.pj
// Unit:    Class edu.rit.pj.CommRequest
//
// This Java source file is copyright (C) 2007 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.
//
// 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.pj;

import edu.rit.mp.IORequest;

import java.io.IOException;

/**
 * Class CommRequest provides an object for doing a non-blocking message passing
 * operation in a PJ cluster parallel program. A non-blocking message passing
 * operation in class {@linkplain Comm} immediately returns a CommRequest object
 * while performing the message passing operation in a separate thread. This
 * allows the calling thread to do other work while the message passing
 * operation is in progress. When the calling thread needs to wait for the
 * message passing operation to finish, the calling thread calls the CommRequest
 * object's waitForFinish() method.
 *
 * @author  Alan Kaminsky
 * @version 18-Sep-2007
 */
public class CommRequest
	{

// Hidden data members.

	IORequest mySendRequest;
	IORequest myRecvRequest;

// Exported constructors.

	/**
	 * Construct a new CommRequest object.
	 */
	public CommRequest()
		{
		}

// Exported operations.

	/**
	 * Determine if the message passing operation associated with this
	 * CommRequest object has finished.
	 * 

	 * Note: If the isFinished() method is called on a
	 * newly-created CommRequest object that has not been passed to or returned
	 * from a communicator's non-blocking send or receive method, the
	 * isFinished() method immediately returns true.
	 *
	 * @return  False if the message passing operation has not finished, true if
	 *          the message passing operation has finished successfully.
	 *
	 * @exception  IOException
	 *     Thrown if the message passing operation has finished and an I/O error
	 *     occurred.
	 */
	public boolean isFinished()
		throws IOException
		{
		return
			(mySendRequest == null || mySendRequest.isFinished()) &&
			(myRecvRequest == null || myRecvRequest.isFinished());
		}

	/**
	 * Wait for the message passing operation associated with this CommRequest
	 * object to finish. If the message passing operation involved a receive, a
	 * {@linkplain CommStatus} object is returned giving the results of the
	 * receive, otherwise null is returned.
	 * 

	 * For a receive operation, the returned status object gives the actual rank
	 * of the process that sent the message, the actual message tag that was
	 * received, and the actual number of data items in the message. If the
	 * actual number of data items in the message is less than the length of the
	 * receive buffer, nothing is stored into the extra data items at the end of
	 * the buffer. If the actual number of data items in the message is greater
	 * than the length of the receive buffer, the extra data items at the end of
	 * the message are discarded.
	 * 

	 * Note: If the waitForFinish() method is called on a
	 * newly-created CommRequest object that has not been passed to or returned
	 * from a communicator's non-blocking send or receive method, the
	 * waitForFinish() method immediately returns null.
	 *
	 * @return  Status object for a receive operation, otherwise null.
	 *
	 * @exception  IOException
	 *     Thrown if an I/O error occurred.
	 */
	public CommStatus waitForFinish()
		throws IOException
		{
		if (mySendRequest != null)
			{
			mySendRequest.waitForFinish();
			}
		if (myRecvRequest != null)
			{
			edu.rit.mp.Status status = myRecvRequest.waitForFinish();
			return new CommStatus
				(Comm.getFarRank (status.channel),
				 status.tag,
				 status.length);
			}
		else
			{
			return null;
			}
		}

	}