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 import sun.misc.Unsafe;
38
39 /**
40 * A {@code long} value that may be updated atomically. See the
41 * {@link java.util.concurrent.atomic} package specification for
42 * description of the properties of atomic variables. An
43 * {@code AtomicLong} is used in applications such as atomically
44 * incremented sequence numbers, and cannot be used as a replacement
45 * for a {@link java.lang.Long}. However, this class does extend
46 * {@code Number} to allow uniform access by tools and utilities that
47 * deal with numerically-based classes.
48 *
49 * @since 1.5
50 * @author Doug Lea
51 */
52 public class AtomicLong extends Number implements java.io.Serializable {
53 private static final long serialVersionUID = 1927816293512124184L;
54
55 // setup to use Unsafe.compareAndSwapLong for updates
56 private static final Unsafe unsafe = Unsafe.getUnsafe();
57 private static final long valueOffset;
58
59 /**
60 * Records whether the underlying JVM supports lockless
61 * compareAndSwap for longs. While the Unsafe.compareAndSwapLong
62 * method works in either case, some constructions should be
63 * handled at Java level to avoid locking user-visible locks.
64 */
65 static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
66
67 /**
68 * Returns whether underlying JVM supports lockless CompareAndSet
69 * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
70 */
71 private static native boolean VMSupportsCS8();
72
73 static {
74 try {
75 valueOffset = unsafe.objectFieldOffset
76 (AtomicLong.class.getDeclaredField("value"));
77 } catch (Exception ex) { throw new Error(ex); }
78 }
79
80 private volatile long value;
81
82 /**
83 * Creates a new AtomicLong with the given initial value.
84 *
85 * @param initialValue the initial value
86 */
87 public AtomicLong(long initialValue) {
88 value = initialValue;
89 }
90
91 /**
92 * Creates a new AtomicLong with initial value {@code 0}.
93 */
94 public AtomicLong() {
95 }
96
97 /**
98 * Gets the current value.
99 *
100 * @return the current value
101 */
102 public final long get() {
103 return value;
104 }
105
106 /**
107 * Sets to the given value.
108 *
109 * @param newValue the new value
110 */
111 public final void set(long newValue) {
112 value = newValue;
113 }
114
115 /**
116 * Eventually sets to the given value.
117 *
118 * @param newValue the new value
119 * @since 1.6
120 */
121 public final void lazySet(long newValue) {
122 unsafe.putOrderedLong(this, valueOffset, newValue);
123 }
124
125 /**
126 * Atomically sets to the given value and returns the old value.
127 *
128 * @param newValue the new value
129 * @return the previous value
130 */
131 public final long getAndSet(long newValue) {
132 while (true) {
133 long current = get();
134 if (compareAndSet(current, newValue))
135 return current;
136 }
137 }
138
139 /**
140 * Atomically sets the value to the given updated value
141 * if the current value {@code ==} the expected value.
142 *
143 * @param expect the expected value
144 * @param update the new value
145 * @return true if successful. False return indicates that
146 * the actual value was not equal to the expected value.
147 */
148 public final boolean compareAndSet(long expect, long update) {
149 return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
150 }
151
152 /**
153 * Atomically sets the value to the given updated value
154 * if the current value {@code ==} the expected value.
155 *
156 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
157 * and does not provide ordering guarantees, so is only rarely an
158 * appropriate alternative to {@code compareAndSet}.
159 *
160 * @param expect the expected value
161 * @param update the new value
162 * @return true if successful.
163 */
164 public final boolean weakCompareAndSet(long expect, long update) {
165 return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
166 }
167
168 /**
169 * Atomically increments by one the current value.
170 *
171 * @return the previous value
172 */
173 public final long getAndIncrement() {
174 while (true) {
175 long current = get();
176 long next = current + 1;
177 if (compareAndSet(current, next))
178 return current;
179 }
180 }
181
182 /**
183 * Atomically decrements by one the current value.
184 *
185 * @return the previous value
186 */
187 public final long getAndDecrement() {
188 while (true) {
189 long current = get();
190 long next = current - 1;
191 if (compareAndSet(current, next))
192 return current;
193 }
194 }
195
196 /**
197 * Atomically adds the given value to the current value.
198 *
199 * @param delta the value to add
200 * @return the previous value
201 */
202 public final long getAndAdd(long delta) {
203 while (true) {
204 long current = get();
205 long next = current + delta;
206 if (compareAndSet(current, next))
207 return current;
208 }
209 }
210
211 /**
212 * Atomically increments by one the current value.
213 *
214 * @return the updated value
215 */
216 public final long incrementAndGet() {
217 for (;;) {
218 long current = get();
219 long next = current + 1;
220 if (compareAndSet(current, next))
221 return next;
222 }
223 }
224
225 /**
226 * Atomically decrements by one the current value.
227 *
228 * @return the updated value
229 */
230 public final long decrementAndGet() {
231 for (;;) {
232 long current = get();
233 long next = current - 1;
234 if (compareAndSet(current, next))
235 return next;
236 }
237 }
238
239 /**
240 * Atomically adds the given value to the current value.
241 *
242 * @param delta the value to add
243 * @return the updated value
244 */
245 public final long addAndGet(long delta) {
246 for (;;) {
247 long current = get();
248 long next = current + delta;
249 if (compareAndSet(current, next))
250 return next;
251 }
252 }
253
254 /**
255 * Returns the String representation of the current value.
256 * @return the String representation of the current value.
257 */
258 public String toString() {
259 return Long.toString(get());
260 }
261
262 /**
263 * Returns the value of this {@code AtomicLong} as an {@code int}
264 * after a narrowing primitive conversion.
265 * @jls 5.1.3 Narrowing Primitive Conversions
266 */
267 public int intValue() {
268 return (int)get();
269 }
270
271 /**
272 * Returns the value of this {@code AtomicLong} as a {@code long}.
273 */
274 public long longValue() {
275 return get();
276 }
277
278 /**
279 * Returns the value of this {@code AtomicLong} as a {@code float}
280 * after a widening primitive conversion.
281 * @jls 5.1.2 Widening Primitive Conversions
282 */
283 public float floatValue() {
284 return (float)get();
285 }
286
287 /**
288 * Returns the value of this {@code AtomicLong} as a {@code double}
289 * after a widening primitive conversion.
290 * @jls 5.1.2 Widening Primitive Conversions
291 */
292 public double doubleValue() {
293 return (double)get();
294 }
295
296 }