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1   //******************************************************************************
2   //
3   // File:    EmptyShortBuf.java
4   // Package: edu.rit.mp.buf
5   // Unit:    Class edu.rit.mp.buf.EmptyShortBuf
6   //
7   // This Java source file is copyright (C) 2007 by Alan Kaminsky. All rights
8   // reserved. For further information, contact the author, Alan Kaminsky, at
9   // ark@cs.rit.edu.
10  //
11  // This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
12  // software; you can redistribute it and/or modify it under the terms of the GNU
13  // General Public License as published by the Free Software Foundation; either
14  // version 3 of the License, or (at your option) any later version.
15  //
16  // PJ is distributed in the hope that it will be useful, but WITHOUT ANY
17  // WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
18  // A PARTICULAR PURPOSE. See the GNU General Public License for more details.
19  //
20  // Linking this library statically or dynamically with other modules is making a
21  // combined work based on this library. Thus, the terms and conditions of the GNU
22  // General Public License cover the whole combination.
23  //
24  // As a special exception, the copyright holders of this library give you
25  // permission to link this library with independent modules to produce an
26  // executable, regardless of the license terms of these independent modules, and
27  // to copy and distribute the resulting executable under terms of your choice,
28  // provided that you also meet, for each linked independent module, the terms
29  // and conditions of the license of that module. An independent module is a module
30  // which is not derived from or based on this library. If you modify this library,
31  // you may extend this exception to your version of the library, but you are not
32  // obligated to do so. If you do not wish to do so, delete this exception
33  // statement from your version.
34  //
35  // A copy of the GNU General Public License is provided in the file gpl.txt. You
36  // may also obtain a copy of the GNU General Public License on the World Wide
37  // Web at http://www.gnu.org/licenses/gpl.html.
38  //
39  //******************************************************************************
40  package edu.rit.mp.buf;
41  
42  import java.nio.ByteBuffer;
43  
44  import edu.rit.mp.Buf;
45  import edu.rit.mp.ShortBuf;
46  import edu.rit.pj.reduction.Op;
47  import edu.rit.pj.reduction.ShortOp;
48  
49  /**
50   * Class EmptyShortBuf provides a short buffer that contains no items for
51   * messages using the Message Protocol (MP). When a message is sent from an
52   * EmptyShortBuf, the message item type is <code>short</code> and the message length
53   * is 0. When a message is received into an EmptyShortBuf, the message item type
54   * must be <code>short</code>, but all items in the message are discarded.
55   *
56   * @author Alan Kaminsky
57   * @version 19-Nov-2007
58   */
59  public class EmptyShortBuf
60          extends ShortBuf {
61  
62  // Exported constructors.
63      /**
64       * Construct a new empty short buffer.
65       */
66      public EmptyShortBuf() {
67          super(0);
68      }
69  
70  // Exported operations.
71      /**
72       * {@inheritDoc}
73       *
74       * Obtain the given item from this buffer.
75       * <P>
76       * The <code>get()</code> method must not block the calling thread; if it does,
77       * all message I/O in MP will be blocked.
78       */
79      public short get(int i) {
80          throw new IndexOutOfBoundsException();
81      }
82  
83      /**
84       * {@inheritDoc}
85       *
86       * Store the given item in this buffer.
87       * <P>
88       * The <code>put()</code> method must not block the calling thread; if it does,
89       * all message I/O in MP will be blocked.
90       */
91      public void put(int i,
92              short item) {
93          throw new IndexOutOfBoundsException();
94      }
95  
96      /**
97       * {@inheritDoc}
98       *
99       * Copy items from the given buffer to this buffer. The number of items
100      * copied is this buffer's length or <code>theSrc</code>'s length, whichever is
101      * smaller. If <code>theSrc</code> is this buffer, the <code>copy()</code> method
102      * does nothing.
103      * @exception ClassCastException (unchecked exception) Thrown if
104      * <code>theSrc</code>'s item data type is not the same as this buffer's item
105      * data type.
106      */
107     public void copy(Buf theSrc) {
108     }
109 
110     /**
111      * {@inheritDoc}
112      *
113      * Create a buffer for performing parallel reduction using the given binary
114      * operation. The results of the reduction are placed into this buffer.
115      * <P>
116      * Operations performed on the returned reduction buffer have the same
117      * effect as operations performed on this buffer, except whenever a source
118      * item <I>S</I> is put into a destination item <I>D</I> in this buffer,
119      * <I>D</I> is set to <I>D op S</I>, that is, the reduction of <I>D</I> and
120      * <I>S</I> using the given binary operation (rather than just setting
121      * <I>D</I> to <I>S</I>).
122      * @exception ClassCastException (unchecked exception) Thrown if this
123      * buffer's element data type and the given binary operation's argument data
124      * type are not the same.
125      */
126     public Buf getReductionBuf(Op op) {
127         ShortOp shortop = (ShortOp) op;
128         return this;
129     }
130 
131 // Hidden operations.
132     /**
133      * {@inheritDoc}
134      *
135      * Send as many items as possible from this buffer to the given byte buffer.
136      * <P>
137      * The <code>sendItems()</code> method must not block the calling thread; if it
138      * does, all message I/O in MP will be blocked.
139      */
140     protected int sendItems(int i,
141             ByteBuffer buffer) {
142         return 0;
143     }
144 
145     /**
146      * {@inheritDoc}
147      *
148      * Receive as many items as possible from the given byte buffer to this
149      * buffer.
150      * <P>
151      * The <code>receiveItems()</code> method must not block the calling thread; if
152      * it does, all message I/O in MP will be blocked.
153      */
154     protected int receiveItems(int i,
155             int num,
156             ByteBuffer buffer) {
157         return 0;
158     }
159 
160 }