1 //******************************************************************************
2 //
3 // File: SharedObject.java
4 // Package: edu.rit.pj.reduction
5 // Unit: Class edu.rit.pj.reduction.SharedObject
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.pj.reduction;
41
42 import java.util.concurrent.atomic.AtomicReference;
43
44 /**
45 * Class SharedObject provides a reduction variable for a value of an object
46 * type.
47 * <P>
48 * Class SharedObject is multiple thread safe. The methods use lock-free atomic
49 * compare-and-set.
50 * <P>
51 * <I>Note:</I> Class SharedObject is implemented using class
52 * java.util.concurrent.atomic.AtomicReference.
53 *
54 * @param <T> Object data type.
55 * @author Alan Kaminsky
56 * @version 20-Jun-2007
57 */
58 public class SharedObject<T> {
59
60 // Hidden data members.
61 private AtomicReference<T> myValue;
62
63 // Exported constructors.
64 /**
65 * Construct a new object reduction variable with the initial value null.
66 */
67 public SharedObject() {
68 myValue = new AtomicReference<T>();
69 }
70
71 /**
72 * Construct a new object reduction variable with the given initial value.
73 *
74 * @param initialValue Initial value.
75 */
76 public SharedObject(T initialValue) {
77 myValue = new AtomicReference<T>(initialValue);
78 }
79
80 // Exported operations.
81 /**
82 * Returns this reduction variable's current value.
83 *
84 * @return Current value.
85 */
86 public T get() {
87 return myValue.get();
88 }
89
90 /**
91 * Set this reduction variable to the given value.
92 *
93 * @param value New value.
94 */
95 public void set(T value) {
96 myValue.set(value);
97 }
98
99 /**
100 * Set this reduction variable to the given value and return the previous
101 * value.
102 *
103 * @param value New value.
104 * @return Previous value.
105 */
106 public T getAndSet(T value) {
107 return myValue.getAndSet(value);
108 }
109
110 /**
111 * Atomically set this reduction variable to the given updated value if the
112 * current value equals the expected value.
113 *
114 * @param expect Expected value.
115 * @param update Updated value.
116 * @return True if the update happened, false otherwise.
117 */
118 public boolean compareAndSet(T expect,
119 T update) {
120 return myValue.compareAndSet(expect, update);
121 }
122
123 /**
124 * Atomically set this reduction variable to the given updated value if the
125 * current value equals the expected value. May fail spuriously.
126 *
127 * @param expect Expected value.
128 * @param update Updated value.
129 * @return True if the update happened, false otherwise.
130 */
131 @SuppressWarnings("deprecation")
132 public boolean weakCompareAndSet(T expect,
133 T update) {
134 return myValue.weakCompareAndSet(expect, update);
135 }
136
137 /**
138 * Combine this reduction variable with the given value using the given
139 * operation. The result is stored back into this reduction variable and is
140 * returned.
141 *
142 * @param value Value.
143 * @param op Binary operation.
144 * @return (This variable) <I>op</I> (<code>value</code>).
145 */
146 public T reduce(T value,
147 ObjectOp<T> op) {
148 for (;;) {
149 T oldvalue = myValue.get();
150 T newvalue = op.op(oldvalue, value);
151 if (myValue.compareAndSet(oldvalue, newvalue)) {
152 return newvalue;
153 }
154 }
155 }
156
157 /**
158 * Returns a string version of this reduction variable.
159 *
160 * @return String version.
161 */
162 public String toString() {
163 return myValue.toString();
164 }
165
166 }