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 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 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 (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 }
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