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1   //******************************************************************************
2   //
3   // File:    EmptyObjectBuf.java
4   // Package: edu.rit.mp.buf
5   // Unit:    Class edu.rit.mp.buf.EmptyObjectBuf
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 edu.rit.mp.Buf;
43  import edu.rit.mp.ObjectBuf;
44  import edu.rit.pj.reduction.ObjectOp;
45  import edu.rit.pj.reduction.Op;
46  
47  /**
48   * Class EmptyObjectBuf provides an object buffer that contains no items for
49   * messages using the Message Protocol (MP). When a message is sent from an
50   * EmptyObjectBuf, the message item type is Object and the message length is 0.
51   * When a message is received into an EmptyObjectBuf, the message item type must
52   * be Object, but all items in the message are discarded.
53   *
54   * @author Alan Kaminsky
55   * @version 03-Jul-2008
56   */
57  public class EmptyObjectBuf
58          extends ObjectBuf<Object> {
59  
60  // Exported constructors.
61      /**
62       * Construct a new empty object buffer.
63       */
64      public EmptyObjectBuf() {
65          super(0);
66      }
67  
68  // Exported operations.
69      /**
70       * {@inheritDoc}
71       *
72       * Obtain the given item from this buffer.
73       * <P>
74       * The <code>get()</code> method must not block the calling thread; if it does,
75       * all message I/O in MP will be blocked.
76       */
77      public Object get(int i) {
78          throw new IndexOutOfBoundsException();
79      }
80  
81      /**
82       * {@inheritDoc}
83       *
84       * Store the given item in this buffer.
85       * <P>
86       * The <code>put()</code> method must not block the calling thread; if it does,
87       * all message I/O in MP will be blocked.
88       */
89      public void put(int i,
90              Object item) {
91          throw new IndexOutOfBoundsException();
92      }
93  
94      /**
95       * {@inheritDoc}
96       *
97       * Copy items from the given buffer to this buffer. The number of items
98       * copied is this buffer's length or <code>theSrc</code>'s length, whichever is
99       * smaller. If <code>theSrc</code> is this buffer, the <code>copy()</code> method
100      * does nothing.
101      * @exception ClassCastException (unchecked exception) Thrown if
102      * <code>theSrc</code>'s item data type is not the same as this buffer's item
103      * data type.
104      */
105     public void copy(Buf theSrc) {
106     }
107 
108     /**
109      * {@inheritDoc}
110      *
111      * Create a buffer for performing parallel reduction using the given binary
112      * operation. The results of the reduction are placed into this buffer.
113      * <P>
114      * Operations performed on the returned reduction buffer have the same
115      * effect as operations performed on this buffer, except whenever a source
116      * item <I>S</I> is put into a destination item <I>D</I> in this buffer,
117      * <I>D</I> is set to <I>D op S</I>, that is, the reduction of <I>D</I> and
118      * <I>S</I> using the given binary operation (rather than just setting
119      * <I>D</I> to <I>S</I>).
120      * @exception ClassCastException (unchecked exception) Thrown if this
121      * buffer's element data type and the given binary operation's argument data
122      * type are not the same.
123      */
124     public Buf getReductionBuf(Op op) {
125         ObjectOp<?> objectop = (ObjectOp<?>) op;
126         return this;
127     }
128 
129 }