rev 12972 : 8140606: Update library code to use internal Unsafe
Reviewed-by: duke

   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 
  38 /**
  39  * A {@code boolean} value that may be updated atomically. See the
  40  * {@link java.util.concurrent.atomic} package specification for
  41  * description of the properties of atomic variables. An
  42  * {@code AtomicBoolean} is used in applications such as atomically
  43  * updated flags, and cannot be used as a replacement for a
  44  * {@link java.lang.Boolean}.
  45  *
  46  * @since 1.5
  47  * @author Doug Lea
  48  */
  49 public class AtomicBoolean implements java.io.Serializable {
  50     private static final long serialVersionUID = 4654671469794556979L;
  51 
  52     private static final jdk.internal.misc.Unsafe U = jdk.internal.misc.Unsafe.getUnsafe();
  53     private static final long VALUE;
  54 
  55     static {
  56         try {
  57             VALUE = U.objectFieldOffset
  58                 (AtomicBoolean.class.getDeclaredField("value"));
  59         } catch (ReflectiveOperationException e) {
  60             throw new Error(e);
  61         }
  62     }
  63 
  64     private volatile int value;
  65 
  66     /**
  67      * Creates a new {@code AtomicBoolean} with the given initial value.
  68      *
  69      * @param initialValue the initial value
  70      */
  71     public AtomicBoolean(boolean initialValue) {
  72         value = initialValue ? 1 : 0;
  73     }
  74 
  75     /**
  76      * Creates a new {@code AtomicBoolean} with initial value {@code false}.
  77      */
  78     public AtomicBoolean() {
  79     }
  80 
  81     /**
  82      * Returns the current value.
  83      *
  84      * @return the current value
  85      */
  86     public final boolean get() {
  87         return value != 0;
  88     }
  89 
  90     /**
  91      * Atomically sets the value to the given updated value
  92      * if the current value {@code ==} the expected value.
  93      *
  94      * @param expect the expected value
  95      * @param update the new value
  96      * @return {@code true} if successful. False return indicates that
  97      * the actual value was not equal to the expected value.
  98      */
  99     public final boolean compareAndSet(boolean expect, boolean update) {
 100         return U.compareAndSwapInt(this, VALUE,
 101                                    (expect ? 1 : 0),
 102                                    (update ? 1 : 0));
 103     }
 104 
 105     /**
 106      * Atomically sets the value to the given updated value
 107      * if the current value {@code ==} the expected value.
 108      *
 109      * <p><a href="package-summary.html#weakCompareAndSet">May fail
 110      * spuriously and does not provide ordering guarantees</a>, so is
 111      * only rarely an appropriate alternative to {@code compareAndSet}.
 112      *
 113      * @param expect the expected value
 114      * @param update the new value
 115      * @return {@code true} if successful
 116      */
 117     public boolean weakCompareAndSet(boolean expect, boolean update) {
 118         return U.compareAndSwapInt(this, VALUE,
 119                                    (expect ? 1 : 0),
 120                                    (update ? 1 : 0));
 121     }
 122 
 123     /**
 124      * Unconditionally sets to the given value.
 125      *
 126      * @param newValue the new value
 127      */
 128     public final void set(boolean newValue) {
 129         value = newValue ? 1 : 0;
 130     }
 131 
 132     /**
 133      * Eventually sets to the given value.
 134      *
 135      * @param newValue the new value
 136      * @since 1.6
 137      */
 138     public final void lazySet(boolean newValue) {
 139         U.putOrderedInt(this, VALUE, (newValue ? 1 : 0));
 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         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      */
 160     public String toString() {
 161         return Boolean.toString(get());
 162     }
 163 
 164 }
--- EOF ---