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
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  */
  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      */
  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      */
  77     public AtomicBoolean() {
  78     }
  79 
  80     /**
  81      * Returns the current value.
  82      *
  83      * @return the current value
  84      */
  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 true if successful. False return indicates that
  96      * the actual value was not equal to the expected value.
  97      */
  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>May <a href="package-summary.html#Spurious">fail spuriously</a>
 109      * and does not provide ordering guarantees, so is only rarely an
 110      * appropriate alternative to {@code compareAndSet}.
 111      *
 112      * @param expect the expected value
 113      * @param update the new value
 114      * @return true if successful.
 115      */
 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      */
 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      */
 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      */
 148     public final boolean getAndSet(boolean newValue) {
 149         for (;;) {
 150             boolean current = get();
 151             if (compareAndSet(current, newValue))
 152                 return current;
 153         }
 154     }
 155 
 156     /**
 157      * Returns the String representation of the current value.
 158      * @return the String representation of the current value.
 159      */
 160     public String toString() {
 161         return Boolean.toString(get());
 162     }
 163 
 164 }