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
|
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent.atomic;
/**
* An object reference that may be updated atomically. See the {@link
* java.util.concurrent.atomic} package specification for description
* of the properties of atomic variables.
* @since 1.5
* @author Doug Lea
* @param <V> The type of object referred to by this reference
*/
public class AtomicReference<V> implements java.io.Serializable {
private static final long serialVersionUID = -1848883965231344442L;
private volatile V value;
/**
* Creates a new AtomicReference with the given initial value.
*
* @param initialValue the initial value
*/
public AtomicReference(V initialValue) {
value = initialValue;
}
/**
* Creates a new AtomicReference with null initial value.
*/
public AtomicReference() {
}
/**
* Gets the current value.
*
* @return the current value
*/
public final V get() {
return value;
}
/**
* Sets to the given value.
*
* @param newValue the new value
*/
public final void set(V newValue) {
value = newValue;
}
/**
* Eventually sets to the given value.
*
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(V newValue) {
value = newValue;
}
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
* @param expect the expected value
* @param update the new value
* @return true if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final native boolean compareAndSet(V expect, V update);
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
*
* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
* and does not provide ordering guarantees, so is only rarely an
* appropriate alternative to {@code compareAndSet}.
*
* @param expect the expected value
* @param update the new value
* @return true if successful.
*/
public final boolean weakCompareAndSet(V expect, V update) {
return compareAndSet(expect, update);
}
/**
* Atomically sets to the given value and returns the old value.
*
* @param newValue the new value
* @return the previous value
*/
public final V getAndSet(V newValue) {
while (true) {
V x = get();
if (compareAndSet(x, newValue))
return x;
}
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value.
*/
public String toString() {
return String.valueOf(get());
}
}
|
