1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
|
//******************************************************************************
//
// File: SharedObject.java
// Package: edu.rit.pj.reduction
// Unit: Class edu.rit.pj.reduction.SharedObject
//
// 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.
//
// Linking this library statically or dynamically with other modules is making a
// combined work based on this library. Thus, the terms and conditions of the
// GNU General Public License cover the whole combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent modules, and
// to copy and distribute the resulting executable under terms of your choice,
// provided that you also meet, for each linked independent module, the terms
// and conditions of the license of that module. An independent module is a
// module which is not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the library, but
// you are not obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
// 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.reduction;
import java.util.concurrent.atomic.AtomicReference;
/**
* Class SharedObject provides a reduction variable for a value of an object
* type.
* <P>
* Class SharedObject is multiple thread safe. The methods use lock-free atomic
* compare-and-set.
* <P>
* <I>Note:</I> Class SharedObject is implemented using class
* java.util.concurrent.atomic.AtomicReference.
*
* @param <T> Object data type.
*
* @author Alan Kaminsky
* @version 20-Jun-2007
*/
public class SharedObject<T>
{
// Hidden data members.
private AtomicReference<T> myValue;
// Exported constructors.
/**
* Construct a new object reduction variable with the initial value null.
*/
public SharedObject()
{
myValue = new AtomicReference<T>();
}
/**
* Construct a new object reduction variable with the given initial value.
*
* @param initialValue Initial value.
*/
public SharedObject
(T initialValue)
{
myValue = new AtomicReference<T> (initialValue);
}
// Exported operations.
/**
* Returns this reduction variable's current value.
*
* @return Current value.
*/
public T get()
{
return myValue.get();
}
/**
* Set this reduction variable to the given value.
*
* @param value New value.
*/
public void set
(T value)
{
myValue.set (value);
}
/**
* Set this reduction variable to the given value and return the previous
* value.
*
* @param value New value.
*
* @return Previous value.
*/
public T getAndSet
(T value)
{
return myValue.getAndSet (value);
}
/**
* Atomically set this reduction variable to the given updated value if the
* current value equals the expected value.
*
* @param expect Expected value.
* @param update Updated value.
*
* @return True if the update happened, false otherwise.
*/
public boolean compareAndSet
(T expect,
T update)
{
return myValue.compareAndSet (expect, update);
}
/**
* Atomically set this reduction variable to the given updated value if the
* current value equals the expected value. May fail spuriously.
*
* @param expect Expected value.
* @param update Updated value.
*
* @return True if the update happened, false otherwise.
*/
public boolean weakCompareAndSet
(T expect,
T update)
{
return myValue.weakCompareAndSet (expect, update);
}
/**
* Combine this reduction variable with the given value using the given
* operation. The result is stored back into this reduction variable and is
* returned.
*
* @param value Value.
* @param op Binary operation.
*
* @return (This variable) <I>op</I> (<TT>value</TT>).
*/
public T reduce
(T value,
ObjectOp<T> op)
{
for (;;)
{
T oldvalue = myValue.get();
T newvalue = op.op (oldvalue, value);
if (myValue.compareAndSet (oldvalue, newvalue)) return newvalue;
}
}
/**
* Returns a string version of this reduction variable.
*
* @return String version.
*/
public String toString()
{
return myValue.toString();
}
}
|
