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.LongBinaryOperator;
39 import java.util.function.LongUnaryOperator;
40
41 /**
42 * A {@code long} value that may be updated atomically. See the
43 * {@link java.util.concurrent.atomic} package specification for
44 * description of the properties of atomic variables. An
45 * {@code AtomicLong} is used in applications such as atomically
46 * incremented sequence numbers, and cannot be used as a replacement
47 * for a {@link java.lang.Long}. However, this class does extend
48 * {@code Number} to allow uniform access by tools and utilities that
49 * deal with numerically-based classes.
50 *
51 * @since 1.5
52 * @author Doug Lea
53 */
54 public class AtomicLong extends Number implements java.io.Serializable {
55 private static final long serialVersionUID = 1927816293512124184L;
56
57 private static final jdk.internal.misc.Unsafe U = jdk.internal.misc.Unsafe.getUnsafe();
58 private static final long VALUE;
59
60 /**
61 * Records whether the underlying JVM supports lockless
62 * compareAndSwap for longs. While the Unsafe.compareAndSwapLong
63 * method works in either case, some constructions should be
64 * handled at Java level to avoid locking user-visible locks.
65 */
66 static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
67
68 /**
69 * Returns whether underlying JVM supports lockless CompareAndSet
70 * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
71 */
72 private static native boolean VMSupportsCS8();
73
74 static {
75 try {
76 VALUE = U.objectFieldOffset
77 (AtomicLong.class.getDeclaredField("value"));
78 } catch (ReflectiveOperationException e) {
79 throw new Error(e);
80 }
81 }
82
83 private volatile long value;
84
85 /**
86 * Creates a new AtomicLong with the given initial value.
87 *
88 * @param initialValue the initial value
89 */
90 public AtomicLong(long initialValue) {
91 value = initialValue;
92 }
93
94 /**
95 * Creates a new AtomicLong with initial value {@code 0}.
96 */
97 public AtomicLong() {
98 }
99
100 /**
101 * Gets the current value.
102 *
103 * @return the current value
104 */
105 public final long get() {
106 return value;
107 }
108
109 /**
110 * Sets to the given value.
111 *
112 * @param newValue the new value
113 */
114 public final void set(long newValue) {
115 // Use putLongVolatile instead of ordinary volatile store when
116 // using compareAndSwapLong, for sake of some 32bit systems.
117 U.putLongVolatile(this, VALUE, newValue);
118 }
119
120 /**
121 * Eventually sets to the given value.
122 *
123 * @param newValue the new value
124 * @since 1.6
125 */
126 public final void lazySet(long newValue) {
127 U.putOrderedLong(this, VALUE, newValue);
128 }
129
130 /**
131 * Atomically sets to the given value and returns the old value.
132 *
133 * @param newValue the new value
134 * @return the previous value
135 */
136 public final long getAndSet(long newValue) {
137 return U.getAndSetLong(this, VALUE, newValue);
138 }
139
140 /**
141 * Atomically sets the value to the given updated value
142 * if the current value {@code ==} the expected value.
143 *
144 * @param expect the expected value
145 * @param update the new value
146 * @return {@code true} if successful. False return indicates that
147 * the actual value was not equal to the expected value.
148 */
149 public final boolean compareAndSet(long expect, long update) {
150 return U.compareAndSwapLong(this, VALUE, expect, update);
151 }
152
153 /**
154 * Atomically sets the value to the given updated value
155 * if the current value {@code ==} the expected value.
156 *
157 * <p><a href="package-summary.html#weakCompareAndSet">May fail
158 * spuriously and does not provide ordering guarantees</a>, so is
159 * only rarely an appropriate alternative to {@code compareAndSet}.
160 *
161 * @param expect the expected value
162 * @param update the new value
163 * @return {@code true} if successful
164 */
165 public final boolean weakCompareAndSet(long expect, long update) {
166 return U.compareAndSwapLong(this, VALUE, expect, update);
167 }
168
169 /**
170 * Atomically increments by one the current value.
171 *
172 * @return the previous value
173 */
174 public final long getAndIncrement() {
175 return U.getAndAddLong(this, VALUE, 1L);
176 }
177
178 /**
179 * Atomically decrements by one the current value.
180 *
181 * @return the previous value
182 */
183 public final long getAndDecrement() {
184 return U.getAndAddLong(this, VALUE, -1L);
185 }
186
187 /**
188 * Atomically adds the given value to the current value.
189 *
190 * @param delta the value to add
191 * @return the previous value
192 */
193 public final long getAndAdd(long delta) {
194 return U.getAndAddLong(this, VALUE, delta);
195 }
196
197 /**
198 * Atomically increments by one the current value.
199 *
200 * @return the updated value
201 */
202 public final long incrementAndGet() {
203 return U.getAndAddLong(this, VALUE, 1L) + 1L;
204 }
205
206 /**
207 * Atomically decrements by one the current value.
208 *
209 * @return the updated value
210 */
211 public final long decrementAndGet() {
212 return U.getAndAddLong(this, VALUE, -1L) - 1L;
213 }
214
215 /**
216 * Atomically adds the given value to the current value.
217 *
218 * @param delta the value to add
219 * @return the updated value
220 */
221 public final long addAndGet(long delta) {
222 return U.getAndAddLong(this, VALUE, delta) + delta;
223 }
224
225 /**
226 * Atomically updates the current value with the results of
227 * applying the given function, returning the previous value. The
228 * function should be side-effect-free, since it may be re-applied
229 * when attempted updates fail due to contention among threads.
230 *
231 * @param updateFunction a side-effect-free function
232 * @return the previous value
233 * @since 1.8
234 */
235 public final long getAndUpdate(LongUnaryOperator updateFunction) {
236 long prev, next;
237 do {
238 prev = get();
239 next = updateFunction.applyAsLong(prev);
240 } while (!compareAndSet(prev, next));
241 return prev;
242 }
243
244 /**
245 * Atomically updates the current value with the results of
246 * applying the given function, returning the updated value. The
247 * function should be side-effect-free, since it may be re-applied
248 * when attempted updates fail due to contention among threads.
249 *
250 * @param updateFunction a side-effect-free function
251 * @return the updated value
252 * @since 1.8
253 */
254 public final long updateAndGet(LongUnaryOperator updateFunction) {
255 long prev, next;
256 do {
257 prev = get();
258 next = updateFunction.applyAsLong(prev);
259 } while (!compareAndSet(prev, next));
260 return next;
261 }
262
263 /**
264 * Atomically updates the current value with the results of
265 * applying the given function to the current and given values,
266 * returning the previous value. The function should be
267 * side-effect-free, since it may be re-applied when attempted
268 * updates fail due to contention among threads. The function
269 * is applied with the current value as its first argument,
270 * and the given update as the second argument.
271 *
272 * @param x the update value
273 * @param accumulatorFunction a side-effect-free function of two arguments
274 * @return the previous value
275 * @since 1.8
276 */
277 public final long getAndAccumulate(long x,
278 LongBinaryOperator accumulatorFunction) {
279 long prev, next;
280 do {
281 prev = get();
282 next = accumulatorFunction.applyAsLong(prev, x);
283 } while (!compareAndSet(prev, next));
284 return prev;
285 }
286
287 /**
288 * Atomically updates the current value with the results of
289 * applying the given function to the current and given values,
290 * returning the updated value. The function should be
291 * side-effect-free, since it may be re-applied when attempted
292 * updates fail due to contention among threads. The function
293 * is applied with the current value as its first argument,
294 * and the given update as the second argument.
295 *
296 * @param x the update value
297 * @param accumulatorFunction a side-effect-free function of two arguments
298 * @return the updated value
299 * @since 1.8
300 */
301 public final long accumulateAndGet(long x,
302 LongBinaryOperator accumulatorFunction) {
303 long prev, next;
304 do {
305 prev = get();
306 next = accumulatorFunction.applyAsLong(prev, x);
307 } while (!compareAndSet(prev, next));
308 return next;
309 }
310
311 /**
312 * Returns the String representation of the current value.
313 * @return the String representation of the current value
314 */
315 public String toString() {
316 return Long.toString(get());
317 }
318
319 /**
320 * Returns the value of this {@code AtomicLong} as an {@code int}
321 * after a narrowing primitive conversion.
322 * @jls 5.1.3 Narrowing Primitive Conversions
323 */
324 public int intValue() {
325 return (int)get();
326 }
327
328 /**
329 * Returns the value of this {@code AtomicLong} as a {@code long}.
330 * Equivalent to {@link #get()}.
331 */
332 public long longValue() {
333 return get();
334 }
335
336 /**
337 * Returns the value of this {@code AtomicLong} as a {@code float}
338 * after a widening primitive conversion.
339 * @jls 5.1.2 Widening Primitive Conversions
340 */
341 public float floatValue() {
342 return (float)get();
343 }
344
345 /**
346 * Returns the value of this {@code AtomicLong} as a {@code double}
347 * after a widening primitive conversion.
348 * @jls 5.1.2 Widening Primitive Conversions
349 */
350 public double doubleValue() {
351 return (double)get();
352 }
353
354 }
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