//******************************************************************************
//
// File:    EmptyShortBuf.java
// Package: edu.rit.mp.buf
// Unit:    Class edu.rit.mp.buf.EmptyShortBuf
//
// 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.mp.buf;

import edu.rit.mp.Buf;
import edu.rit.mp.ShortBuf;

import edu.rit.pj.reduction.ShortOp;
import edu.rit.pj.reduction.Op;

import java.nio.ByteBuffer;

/**
 * Class EmptyShortBuf provides a short buffer that contains no items for
 * messages using the Message Protocol (MP). When a message is sent from an
 * EmptyShortBuf, the message item type is short and the message
 * length is 0. When a message is received into an EmptyShortBuf, the message
 * item type must be short, but all items in the message are
 * discarded.
 *
 * @author  Alan Kaminsky
 * @version 19-Nov-2007
 */
public class EmptyShortBuf
	extends ShortBuf
	{

// Exported constructors.

	/**
	 * Construct a new empty short buffer.
	 */
	public EmptyShortBuf()
		{
		super (0);
		}

// Exported operations.

	/**
	 * Obtain the given item from this buffer.
	 * 

	 * The get() method must not block the calling thread; if it does,
	 * all message I/O in MP will be blocked.
	 *
	 * @param  i  Item index in the range 0 .. length()-1.
	 *
	 * @return  Item at index i.
	 */
	public short get
		(int i)
		{
		throw new IndexOutOfBoundsException();
		}

	/**
	 * Store the given item in this buffer.
	 * 

	 * The put() method must not block the calling thread; if it does,
	 * all message I/O in MP will be blocked.
	 *
	 * @param  i     Item index in the range 0 .. length()-1.
	 * @param  item  Item to be stored at index i.
	 */
	public void put
		(int i,
		 short item)
		{
		throw new IndexOutOfBoundsException();
		}

	/**
	 * Copy items from the given buffer to this buffer. The number of items
	 * copied is this buffer's length or theSrc's length, whichever is
	 * smaller. If theSrc is this buffer, the copy() method
	 * does nothing.
	 *
	 * @param  theSrc  Source of items to copy into this buffer.
	 *
	 * @exception  ClassCastException
	 *     (unchecked exception) Thrown if theSrc's item data type is
	 *     not the same as this buffer's item data type.
	 */
	public void copy
		(Buf theSrc)
		{
		}

	/**
	 * Create a buffer for performing parallel reduction using the given binary
	 * operation. The results of the reduction are placed into this buffer.
	 * 

	 * Operations performed on the returned reduction buffer have the same
	 * effect as operations performed on this buffer, except whenever a source
	 * item S is put into a destination item D in this buffer,
	 * D is set to D op S, that is, the reduction of D and
	 * S using the given binary operation (rather than just setting
	 * D to S).
	 *
	 * @param  op  Binary operation.
	 *
	 * @exception  ClassCastException
	 *     (unchecked exception) Thrown if this buffer's element data type and
	 *     the given binary operation's argument data type are not the same.
	 */
	public Buf getReductionBuf
		(Op op)
		{
		ShortOp shortop = (ShortOp) op;
		return this;
		}

// Hidden operations.

	/**
	 * Send as many items as possible from this buffer to the given byte
	 * buffer.
	 * 

	 * The sendItems() method must not block the calling thread; if it
	 * does, all message I/O in MP will be blocked.
	 *
	 * @param  i       Index of first item to send, in the range 0 ..
	 *                 length-1.
	 * @param  buffer  Byte buffer.
	 *
	 * @return  Number of items sent.
	 */
	protected int sendItems
		(int i,
		 ByteBuffer buffer)
		{
		return 0;
		}

	/**
	 * Receive as many items as possible from the given byte buffer to this
	 * buffer.
	 * 

	 * The receiveItems() method must not block the calling thread; if
	 * it does, all message I/O in MP will be blocked.
	 *
	 * @param  i       Index of first item to receive, in the range 0 ..
	 *                 length-1.
	 * @param  num     Maximum number of items to receive.
	 * @param  buffer  Byte buffer.
	 *
	 * @return  Number of items received.
	 */
	protected int receiveItems
		(int i,
		 int num,
		 ByteBuffer buffer)
		{
		return 0;
		}

	}