1 //******************************************************************************
2 //
3 // File: EmptyByteBuf.java
4 // Package: edu.rit.mp.buf
5 // Unit: Class edu.rit.mp.buf.EmptyByteBuf
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.ByteBuf;
46 import edu.rit.pj.reduction.ByteOp;
47 import edu.rit.pj.reduction.Op;
48
49 /**
50 * Class EmptyByteBuf provides a byte buffer that contains no items for messages
51 * using the Message Protocol (MP). When a message is sent from an EmptyByteBuf,
52 * the message item type is <code>byte</code> and the message length is 0. When a
53 * message is received into an EmptyByteBuf, the message item type must be
54 * <code>byte</code>, but all items in the message are discarded.
55 *
56 * @author Alan Kaminsky
57 * @version 19-Nov-2007
58 */
59 public class EmptyByteBuf
60 extends ByteBuf {
61
62 // Exported constructors.
63 /**
64 * Construct a new empty byte buffer.
65 */
66 public EmptyByteBuf() {
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 byte 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 byte 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 ByteOp byteop = (ByteOp) 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 }