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 sun.misc.Unsafe U = sun.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 } 165
