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 import java.util.function.BinaryOperator; 39 import java.util.function.UnaryOperator; 40 41 /** 42 * An object reference that may be updated atomically. See the {@link 43 * java.util.concurrent.atomic} package specification for description 44 * of the properties of atomic variables. 45 * @since 1.5 46 * @author Doug Lea 47 * @param <V> The type of object referred to by this reference 48 */ 49 public class AtomicReference<V> implements java.io.Serializable { 50 private static final long serialVersionUID = -1848883965231344442L; 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 (AtomicReference.class.getDeclaredField("value")); 59 } catch (ReflectiveOperationException e) { 60 throw new Error(e); 61 } 62 } 63 64 private volatile V value; 65 66 /** 67 * Creates a new AtomicReference with the given initial value. 68 * 69 * @param initialValue the initial value 70 */ 71 public AtomicReference(V initialValue) { 72 value = initialValue; 73 } 74 75 /** 76 * Creates a new AtomicReference with null initial value. 77 */ 78 public AtomicReference() { 79 } 80 81 /** 82 * Gets the current value. 83 * 84 * @return the current value 85 */ 86 public final V get() { 87 return value; 88 } 89 90 /** 91 * Sets to the given value. 92 * 93 * @param newValue the new value 94 */ 95 public final void set(V newValue) { 96 value = newValue; 97 } 98 99 /** 100 * Eventually sets to the given value. 101 * 102 * @param newValue the new value 103 * @since 1.6 104 */ 105 public final void lazySet(V newValue) { 106 U.putOrderedObject(this, VALUE, newValue); 107 } 108 109 /** 110 * Atomically sets the value to the given updated value 111 * if the current value {@code ==} the expected value. 112 * @param expect the expected value 113 * @param update the new value 114 * @return {@code true} if successful. False return indicates that 115 * the actual value was not equal to the expected value. 116 */ 117 public final boolean compareAndSet(V expect, V update) { 118 return U.compareAndSwapObject(this, VALUE, expect, update); 119 } 120 121 /** 122 * Atomically sets the value to the given updated value 123 * if the current value {@code ==} the expected value. 124 * 125 * <p><a href="package-summary.html#weakCompareAndSet">May fail 126 * spuriously and does not provide ordering guarantees</a>, so is 127 * only rarely an appropriate alternative to {@code compareAndSet}. 128 * 129 * @param expect the expected value 130 * @param update the new value 131 * @return {@code true} if successful 132 */ 133 public final boolean weakCompareAndSet(V expect, V update) { 134 return U.compareAndSwapObject(this, VALUE, expect, update); 135 } 136 137 /** 138 * Atomically sets to the given value and returns the old value. 139 * 140 * @param newValue the new value 141 * @return the previous value 142 */ 143 @SuppressWarnings("unchecked") 144 public final V getAndSet(V newValue) { 145 return (V)U.getAndSetObject(this, VALUE, newValue); 146 } 147 148 /** 149 * Atomically updates the current value with the results of 150 * applying the given function, returning the previous value. The 151 * function should be side-effect-free, since it may be re-applied 152 * when attempted updates fail due to contention among threads. 153 * 154 * @param updateFunction a side-effect-free function 155 * @return the previous value 156 * @since 1.8 157 */ 158 public final V getAndUpdate(UnaryOperator<V> updateFunction) { 159 V prev, next; 160 do { 161 prev = get(); 162 next = updateFunction.apply(prev); 163 } while (!compareAndSet(prev, next)); 164 return prev; 165 } 166 167 /** 168 * Atomically updates the current value with the results of 169 * applying the given function, returning the updated value. The 170 * function should be side-effect-free, since it may be re-applied 171 * when attempted updates fail due to contention among threads. 172 * 173 * @param updateFunction a side-effect-free function 174 * @return the updated value 175 * @since 1.8 176 */ 177 public final V updateAndGet(UnaryOperator<V> updateFunction) { 178 V prev, next; 179 do { 180 prev = get(); 181 next = updateFunction.apply(prev); 182 } while (!compareAndSet(prev, next)); 183 return next; 184 } 185 186 /** 187 * Atomically updates the current value with the results of 188 * applying the given function to the current and given values, 189 * returning the previous value. The function should be 190 * side-effect-free, since it may be re-applied when attempted 191 * updates fail due to contention among threads. The function 192 * is applied with the current value as its first argument, 193 * and the given update as the second argument. 194 * 195 * @param x the update value 196 * @param accumulatorFunction a side-effect-free function of two arguments 197 * @return the previous value 198 * @since 1.8 199 */ 200 public final V getAndAccumulate(V x, 201 BinaryOperator<V> accumulatorFunction) { 202 V prev, next; 203 do { 204 prev = get(); 205 next = accumulatorFunction.apply(prev, x); 206 } while (!compareAndSet(prev, next)); 207 return prev; 208 } 209 210 /** 211 * Atomically updates the current value with the results of 212 * applying the given function to the current and given values, 213 * returning the updated value. The function should be 214 * side-effect-free, since it may be re-applied when attempted 215 * updates fail due to contention among threads. The function 216 * is applied with the current value as its first argument, 217 * and the given update as the second argument. 218 * 219 * @param x the update value 220 * @param accumulatorFunction a side-effect-free function of two arguments 221 * @return the updated value 222 * @since 1.8 223 */ 224 public final V accumulateAndGet(V x, 225 BinaryOperator<V> accumulatorFunction) { 226 V prev, next; 227 do { 228 prev = get(); 229 next = accumulatorFunction.apply(prev, x); 230 } while (!compareAndSet(prev, next)); 231 return next; 232 } 233 234 /** 235 * Returns the String representation of the current value. 236 * @return the String representation of the current value 237 */ 238 public String toString() { 239 return String.valueOf(get()); 240 } 241 242 } 243
