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 java.util.functions.IntUnaryOperator;
38 import sun.misc.Unsafe;
39
40 /**
41 * An {@code int} value that may be updated atomically. See the
42 * {@link java.util.concurrent.atomic} package specification for
43 * description of the properties of atomic variables. An
44 * {@code AtomicInteger} is used in applications such as atomically
45 * incremented counters, and cannot be used as a replacement for an
46 * {@link java.lang.Integer}. However, this class does extend
47 * {@code Number} to allow uniform access by tools and utilities that
48 * deal with numerically-based classes.
49 *
50 * @since 1.5
51 * @author Doug Lea
52 */
53 public class AtomicInteger extends Number implements java.io.Serializable {
54 private static final long serialVersionUID = 6214790243416807050L;
55
56 // setup to use Unsafe.compareAndSwapInt for updates
57 private static final Unsafe unsafe = Unsafe.getUnsafe();
58 private static final long valueOffset;
59
60 static {
61 try {
62 valueOffset = unsafe.objectFieldOffset
63 (AtomicInteger.class.getDeclaredField("value"));
64 } catch (Exception ex) { throw new Error(ex); }
65 }
66
67 private volatile int value;
68
69 /**
70 * Creates a new AtomicInteger with the given initial value.
71 *
72 * @param initialValue the initial value
73 */
74 public AtomicInteger(int initialValue) {
75 value = initialValue;
76 }
77
78 /**
79 * Creates a new AtomicInteger with initial value {@code 0}.
80 */
81 public AtomicInteger() {
82 }
83
84 /**
85 * Gets the current value.
86 *
87 * @return the current value
88 */
89 public final int get() {
90 return value;
91 }
92
93 /**
94 * Sets to the given value.
95 *
96 * @param newValue the new value
97 */
98 public final void set(int newValue) {
99 value = newValue;
100 }
101
102 /**
103 * Eventually sets to the given value.
104 *
105 * @param newValue the new value
106 * @since 1.6
107 */
108 public final void lazySet(int newValue) {
109 unsafe.putOrderedInt(this, valueOffset, newValue);
110 }
111
112 /**
113 * Atomically sets to the given value and returns the old value.
114 *
115 * @param newValue the new value
116 * @return the previous value
117 */
118 public final int getAndSet(int newValue) {
119 for (;;) {
120 int current = get();
121 if (compareAndSet(current, newValue))
122 return current;
123 }
124 }
125
126 /**
127 * Atomically sets the value to the given updated value
128 * if the current value {@code ==} the expected value.
129 *
130 * @param expect the expected value
131 * @param update the new value
132 * @return true if successful. False return indicates that
133 * the actual value was not equal to the expected value.
134 */
135 public final boolean compareAndSet(int expect, int update) {
136 return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
137 }
138
139 /**
140 * Sets the value by applying the supplied operator to the old value,
141 * and updating it atomically as in {@link #compareAndSet(int, int)}.
142 *
143 * If the update results in a collision, we back off and retry the update
144 * (using the new current value) until successful.
145 *
146 * @param op the operator to use to compute the new value
147 * @return the old value
148 */
149 public final int getAndUpdate(IntUnaryOperator op) {
150 int oldValue, newValue;
151 do {
152 oldValue = get();
153 newValue = op.operate(oldValue);
154 } while (!compareAndSet(oldValue, newValue));
155 return oldValue;
156 }
157
158 /**
159 * Sets the value by applying the supplied operator to the old value,
160 * and updating it atomically as in {@link #compareAndSet(int, int)}.
161 *
162 * If the update results in a collision, we back off and retry the update
163 * (using the new current value) until successful.
164 *
165 * @param op the operator to use to compute the new value
166 * @return the new value
167 */
168 public final int updateAndGet(IntUnaryOperator op) {
169 int oldValue, newValue;
170 do {
171 oldValue = get();
172 newValue = op.operate(oldValue);
173 } while (!compareAndSet(oldValue, newValue));
174 return newValue;
175 }
176
177 /**
178 * Atomically sets the value to the given updated value
179 * if the current value {@code ==} the expected value.
180 *
181 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
182 * and does not provide ordering guarantees, so is only rarely an
183 * appropriate alternative to {@code compareAndSet}.
184 *
185 * @param expect the expected value
186 * @param update the new value
187 * @return true if successful.
188 */
189 public final boolean weakCompareAndSet(int expect, int update) {
190 return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
191 }
192
193 /**
194 * Atomically increments by one the current value.
195 *
196 * @return the previous value
197 */
198 public final int getAndIncrement() {
199 for (;;) {
200 int current = get();
201 int next = current + 1;
202 if (compareAndSet(current, next))
203 return current;
204 }
205 }
206
207 /**
208 * Atomically decrements by one the current value.
209 *
210 * @return the previous value
211 */
212 public final int getAndDecrement() {
213 for (;;) {
214 int current = get();
215 int next = current - 1;
216 if (compareAndSet(current, next))
217 return current;
218 }
219 }
220
221 /**
222 * Atomically adds the given value to the current value.
223 *
224 * @param delta the value to add
225 * @return the previous value
226 */
227 public final int getAndAdd(int delta) {
228 for (;;) {
229 int current = get();
230 int next = current + delta;
231 if (compareAndSet(current, next))
232 return current;
233 }
234 }
235
236 /**
237 * Atomically increments by one the current value.
238 *
239 * @return the updated value
240 */
241 public final int incrementAndGet() {
242 for (;;) {
243 int current = get();
244 int next = current + 1;
245 if (compareAndSet(current, next))
246 return next;
247 }
248 }
249
250 /**
251 * Atomically decrements by one the current value.
252 *
253 * @return the updated value
254 */
255 public final int decrementAndGet() {
256 for (;;) {
257 int current = get();
258 int next = current - 1;
259 if (compareAndSet(current, next))
260 return next;
261 }
262 }
263
264 /**
265 * Atomically adds the given value to the current value.
266 *
267 * @param delta the value to add
268 * @return the updated value
269 */
270 public final int addAndGet(int delta) {
271 for (;;) {
272 int current = get();
273 int next = current + delta;
274 if (compareAndSet(current, next))
275 return next;
276 }
277 }
278
279 /**
280 * Returns the String representation of the current value.
281 * @return the String representation of the current value.
282 */
283 public String toString() {
284 return Integer.toString(get());
285 }
286
287
288 /**
289 * Returns the value of this {@code AtomicInteger} as an {@code int}.
290 */
291 public int intValue() {
292 return get();
293 }
294
295 /**
296 * Returns the value of this {@code AtomicInteger} as a {@code long}
297 * after a widening primitive conversion.
298 * @jls 5.1.2 Widening Primitive Conversions
299 */
300 public long longValue() {
301 return (long)get();
302 }
303
304 /**
305 * Returns the value of this {@code AtomicInteger} as a {@code float}
306 * after a widening primitive conversion.
307 * @jls 5.1.2 Widening Primitive Conversions
308 */
309 public float floatValue() {
310 return (float)get();
311 }
312
313 /**
314 * Returns the value of this {@code AtomicInteger} as a {@code double}
315 * after a widening primitive conversion.
316 * @jls 5.1.2 Widening Primitive Conversions
317 */
318 public double doubleValue() {
319 return (double)get();
320 }
321
322 }