1 /*
2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3  *
4  * This code is free software; you can redistribute it and/or modify it
5  * under the terms of the GNU General Public License version 2 only, as
6  * published by the Free Software Foundation.  Oracle designates this
7  * particular file as subject to the "Classpath" exception as provided
8  * by Oracle in the LICENSE file that accompanied this code.
9  *
10  * This code is distributed in the hope that it will be useful, but WITHOUT
11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13  * version 2 for more details (a copy is included in the LICENSE file that
14  * accompanied this code).
15  *
16  * You should have received a copy of the GNU General Public License version
17  * 2 along with this work; if not, write to the Free Software Foundation,
18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19  *
20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24 
25 /*
26  * This file is available under and governed by the GNU General Public
27  * License version 2 only, as published by the Free Software Foundation.
28  * However, the following notice accompanied the original version of this
29  * file:
30  *
31  * Written by Doug Lea with assistance from members of JCP JSR-166
32  * Expert Group and released to the public domain, as explained at
33  * http://creativecommons.org/publicdomain/zero/1.0/
34  */
35 
36 package java.util.concurrent.atomic;
37 import sun.misc.Unsafe;
38 
39 /**
40  * A {@code boolean} value that may be updated atomically. See the
41  * {@link java.util.concurrent.atomic} package specification for
42  * description of the properties of atomic variables. An
43  * {@code AtomicBoolean} is used in applications such as atomically
44  * updated flags, and cannot be used as a replacement for a
45  * {@link java.lang.Boolean}.
46  *
47  * @since 1.5
48  * @author Doug Lea
49  */
50 public class AtomicBoolean implements java.io.Serializable {
51     private static final long serialVersionUID = 4654671469794556979L;
52     // setup to use Unsafe.compareAndSwapInt for updates
53     private static final Unsafe unsafe = Unsafe.getUnsafe();
54     private static final long valueOffset;
55 
56     static {
57         try {
58             valueOffset = unsafe.objectFieldOffset
59                 (AtomicBoolean.class.getDeclaredField("value"));
60         } catch (Exception ex) { throw new Error(ex); }
61     }
62 
63     private volatile int value;
64 
65     /**
66      * Creates a new {@code AtomicBoolean} with the given initial value.
67      *
68      * @param initialValue the initial value
69      */
AtomicBoolean(boolean initialValue)70     public AtomicBoolean(boolean initialValue) {
71         value = initialValue ? 1 : 0;
72     }
73 
74     /**
75      * Creates a new {@code AtomicBoolean} with initial value {@code false}.
76      */
AtomicBoolean()77     public AtomicBoolean() {
78     }
79 
80     /**
81      * Returns the current value.
82      *
83      * @return the current value
84      */
get()85     public final boolean get() {
86         return value != 0;
87     }
88 
89     /**
90      * Atomically sets the value to the given updated value
91      * if the current value {@code ==} the expected value.
92      *
93      * @param expect the expected value
94      * @param update the new value
95      * @return {@code true} if successful. False return indicates that
96      * the actual value was not equal to the expected value.
97      */
compareAndSet(boolean expect, boolean update)98     public final boolean compareAndSet(boolean expect, boolean update) {
99         int e = expect ? 1 : 0;
100         int u = update ? 1 : 0;
101         return unsafe.compareAndSwapInt(this, valueOffset, e, u);
102     }
103 
104     /**
105      * Atomically sets the value to the given updated value
106      * if the current value {@code ==} the expected value.
107      *
108      * <p><a href="package-summary.html#weakCompareAndSet">May fail
109      * spuriously and does not provide ordering guarantees</a>, so is
110      * only rarely an appropriate alternative to {@code compareAndSet}.
111      *
112      * @param expect the expected value
113      * @param update the new value
114      * @return {@code true} if successful
115      */
weakCompareAndSet(boolean expect, boolean update)116     public boolean weakCompareAndSet(boolean expect, boolean update) {
117         int e = expect ? 1 : 0;
118         int u = update ? 1 : 0;
119         return unsafe.compareAndSwapInt(this, valueOffset, e, u);
120     }
121 
122     /**
123      * Unconditionally sets to the given value.
124      *
125      * @param newValue the new value
126      */
set(boolean newValue)127     public final void set(boolean newValue) {
128         value = newValue ? 1 : 0;
129     }
130 
131     /**
132      * Eventually sets to the given value.
133      *
134      * @param newValue the new value
135      * @since 1.6
136      */
lazySet(boolean newValue)137     public final void lazySet(boolean newValue) {
138         int v = newValue ? 1 : 0;
139         unsafe.putOrderedInt(this, valueOffset, v);
140     }
141 
142     /**
143      * Atomically sets to the given value and returns the previous value.
144      *
145      * @param newValue the new value
146      * @return the previous value
147      */
getAndSet(boolean newValue)148     public final boolean getAndSet(boolean newValue) {
149         boolean prev;
150         do {
151             prev = get();
152         } while (!compareAndSet(prev, newValue));
153         return prev;
154     }
155 
156     /**
157      * Returns the String representation of the current value.
158      * @return the String representation of the current value
159      */
toString()160     public String toString() {
161         return Boolean.toString(get());
162     }
163 
164 }
165