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Java Source Code / Java Documentation » 6.0 JDK Core » Collections Jar Zip Logging regex » java.util.concurrent.atomic 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001        /*
002         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
003         *
004         * This code is free software; you can redistribute it and/or modify it
005         * under the terms of the GNU General Public License version 2 only, as
006         * published by the Free Software Foundation.  Sun designates this
007         * particular file as subject to the "Classpath" exception as provided
008         * by Sun in the LICENSE file that accompanied this code.
009         *
010         * This code is distributed in the hope that it will be useful, but WITHOUT
011         * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
012         * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
013         * version 2 for more details (a copy is included in the LICENSE file that
014         * accompanied this code).
015         *
016         * You should have received a copy of the GNU General Public License version
017         * 2 along with this work; if not, write to the Free Software Foundation,
018         * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
019         *
020         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
021         * CA 95054 USA or visit www.sun.com if you need additional information or
022         * have any questions.
023         */
024
025        /*
026         * This file is available under and governed by the GNU General Public
027         * License version 2 only, as published by the Free Software Foundation.
028         * However, the following notice accompanied the original version of this
029         * file:
030         *
031         * Written by Doug Lea with assistance from members of JCP JSR-166
032         * Expert Group and released to the public domain, as explained at
033         * http://creativecommons.org/licenses/publicdomain
034         */
035
036        package java.util.concurrent.atomic;
037
038        import sun.misc.Unsafe;
039
040        /**
041         * An {@code int} value that may be updated atomically.  See the
042         * {@link java.util.concurrent.atomic} package specification for
043         * description of the properties of atomic variables. An
044         * {@code AtomicInteger} is used in applications such as atomically
045         * incremented counters, and cannot be used as a replacement for an
046         * {@link java.lang.Integer}. However, this class does extend
047         * {@code Number} to allow uniform access by tools and utilities that
048         * deal with numerically-based classes.
049         *
050         * @since 1.5
051         * @author Doug Lea
052         */
053        public class AtomicInteger extends Number implements 
054                java.io.Serializable {
055            private static final long serialVersionUID = 6214790243416807050L;
056
057            // setup to use Unsafe.compareAndSwapInt for updates
058            private static final Unsafe unsafe = Unsafe.getUnsafe();
059            private static final long valueOffset;
060
061            static {
062                try {
063                    valueOffset = unsafe.objectFieldOffset(AtomicInteger.class
064                            .getDeclaredField("value"));
065                } catch (Exception ex) {
066                    throw new Error(ex);
067                }
068            }
069
070            private volatile int value;
071
072            /**
073             * Creates a new AtomicInteger with the given initial value.
074             *
075             * @param initialValue the initial value
076             */
077            public AtomicInteger(int initialValue) {
078                value = initialValue;
079            }
080
081            /**
082             * Creates a new AtomicInteger with initial value {@code 0}.
083             */
084            public AtomicInteger() {
085            }
086
087            /**
088             * Gets the current value.
089             *
090             * @return the current value
091             */
092            public final int get() {
093                return value;
094            }
095
096            /**
097             * Sets to the given value.
098             *
099             * @param newValue the new value
100             */
101            public final void set(int newValue) {
102                value = newValue;
103            }
104
105            /**
106             * Eventually sets to the given value.
107             *
108             * @param newValue the new value
109             * @since 1.6
110             */
111            public final void lazySet(int newValue) {
112                unsafe.putOrderedInt(this , valueOffset, newValue);
113            }
114
115            /**
116             * Atomically sets to the given value and returns the old value.
117             *
118             * @param newValue the new value
119             * @return the previous value
120             */
121            public final int getAndSet(int newValue) {
122                for (;;) {
123                    int current = get();
124                    if (compareAndSet(current, newValue))
125                        return current;
126                }
127            }
128
129            /**
130             * Atomically sets the value to the given updated value
131             * if the current value {@code ==} the expected value.
132             *
133             * @param expect the expected value
134             * @param update the new value
135             * @return true if successful. False return indicates that
136             * the actual value was not equal to the expected value.
137             */
138            public final boolean compareAndSet(int expect, int update) {
139                return unsafe.compareAndSwapInt(this , valueOffset, expect,
140                        update);
141            }
142
143            /**
144             * Atomically sets the value to the given updated value
145             * if the current value {@code ==} the expected value.
146             *
147             * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
148             * and does not provide ordering guarantees, so is only rarely an
149             * appropriate alternative to {@code compareAndSet}.
150             *
151             * @param expect the expected value
152             * @param update the new value
153             * @return true if successful.
154             */
155            public final boolean weakCompareAndSet(int expect, int update) {
156                return unsafe.compareAndSwapInt(this , valueOffset, expect,
157                        update);
158            }
159
160            /**
161             * Atomically increments by one the current value.
162             *
163             * @return the previous value
164             */
165            public final int getAndIncrement() {
166                for (;;) {
167                    int current = get();
168                    int next = current + 1;
169                    if (compareAndSet(current, next))
170                        return current;
171                }
172            }
173
174            /**
175             * Atomically decrements by one the current value.
176             *
177             * @return the previous value
178             */
179            public final int getAndDecrement() {
180                for (;;) {
181                    int current = get();
182                    int next = current - 1;
183                    if (compareAndSet(current, next))
184                        return current;
185                }
186            }
187
188            /**
189             * Atomically adds the given value to the current value.
190             *
191             * @param delta the value to add
192             * @return the previous value
193             */
194            public final int getAndAdd(int delta) {
195                for (;;) {
196                    int current = get();
197                    int next = current + delta;
198                    if (compareAndSet(current, next))
199                        return current;
200                }
201            }
202
203            /**
204             * Atomically increments by one the current value.
205             *
206             * @return the updated value
207             */
208            public final int incrementAndGet() {
209                for (;;) {
210                    int current = get();
211                    int next = current + 1;
212                    if (compareAndSet(current, next))
213                        return next;
214                }
215            }
216
217            /**
218             * Atomically decrements by one the current value.
219             *
220             * @return the updated value
221             */
222            public final int decrementAndGet() {
223                for (;;) {
224                    int current = get();
225                    int next = current - 1;
226                    if (compareAndSet(current, next))
227                        return next;
228                }
229            }
230
231            /**
232             * Atomically adds the given value to the current value.
233             *
234             * @param delta the value to add
235             * @return the updated value
236             */
237            public final int addAndGet(int delta) {
238                for (;;) {
239                    int current = get();
240                    int next = current + delta;
241                    if (compareAndSet(current, next))
242                        return next;
243                }
244            }
245
246            /**
247             * Returns the String representation of the current value.
248             * @return the String representation of the current value.
249             */
250            public String toString() {
251                return Integer.toString(get());
252            }
253
254            public int intValue() {
255                return get();
256            }
257
258            public long longValue() {
259                return (long) get();
260            }
261
262            public float floatValue() {
263                return (float) get();
264            }
265
266            public double doubleValue() {
267                return (double) get();
268            }
269
270        }
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