| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/licenses/publicdomain |
| */ |
| |
| package java.util.concurrent.atomic; |
| |
| /** |
| * An {@code AtomicStampedReference} maintains an object reference |
| * along with an integer "stamp", that can be updated atomically. |
| * |
| * <p> Implementation note. This implementation maintains stamped |
| * references by creating internal objects representing "boxed" |
| * [reference, integer] pairs. |
| * |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <V> The type of object referred to by this reference |
| */ |
| public class AtomicStampedReference<V> { |
| |
| private static class ReferenceIntegerPair<T> { |
| private final T reference; |
| private final int integer; |
| ReferenceIntegerPair(T r, int i) { |
| reference = r; integer = i; |
| } |
| } |
| |
| private final AtomicReference<ReferenceIntegerPair<V>> atomicRef; |
| |
| /** |
| * Creates a new {@code AtomicStampedReference} with the given |
| * initial values. |
| * |
| * @param initialRef the initial reference |
| * @param initialStamp the initial stamp |
| */ |
| public AtomicStampedReference(V initialRef, int initialStamp) { |
| atomicRef = new AtomicReference<ReferenceIntegerPair<V>> |
| (new ReferenceIntegerPair<V>(initialRef, initialStamp)); |
| } |
| |
| /** |
| * Returns the current value of the reference. |
| * |
| * @return the current value of the reference |
| */ |
| public V getReference() { |
| return atomicRef.get().reference; |
| } |
| |
| /** |
| * Returns the current value of the stamp. |
| * |
| * @return the current value of the stamp |
| */ |
| public int getStamp() { |
| return atomicRef.get().integer; |
| } |
| |
| /** |
| * Returns the current values of both the reference and the stamp. |
| * Typical usage is {@code int[1] holder; ref = v.get(holder); }. |
| * |
| * @param stampHolder an array of size of at least one. On return, |
| * {@code stampholder[0]} will hold the value of the stamp. |
| * @return the current value of the reference |
| */ |
| public V get(int[] stampHolder) { |
| ReferenceIntegerPair<V> p = atomicRef.get(); |
| stampHolder[0] = p.integer; |
| return p.reference; |
| } |
| |
| /** |
| * Atomically sets the value of both the reference and stamp |
| * to the given update values if the |
| * current reference is {@code ==} to the expected reference |
| * and the current stamp is equal to the expected stamp. |
| * |
| * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
| * and does not provide ordering guarantees, so is only rarely an |
| * appropriate alternative to {@code compareAndSet}. |
| * |
| * @param expectedReference the expected value of the reference |
| * @param newReference the new value for the reference |
| * @param expectedStamp the expected value of the stamp |
| * @param newStamp the new value for the stamp |
| * @return true if successful |
| */ |
| public boolean weakCompareAndSet(V expectedReference, |
| V newReference, |
| int expectedStamp, |
| int newStamp) { |
| ReferenceIntegerPair<V> current = atomicRef.get(); |
| return expectedReference == current.reference && |
| expectedStamp == current.integer && |
| ((newReference == current.reference && |
| newStamp == current.integer) || |
| atomicRef.weakCompareAndSet(current, |
| new ReferenceIntegerPair<V>(newReference, |
| newStamp))); |
| } |
| |
| /** |
| * Atomically sets the value of both the reference and stamp |
| * to the given update values if the |
| * current reference is {@code ==} to the expected reference |
| * and the current stamp is equal to the expected stamp. |
| * |
| * @param expectedReference the expected value of the reference |
| * @param newReference the new value for the reference |
| * @param expectedStamp the expected value of the stamp |
| * @param newStamp the new value for the stamp |
| * @return true if successful |
| */ |
| public boolean compareAndSet(V expectedReference, |
| V newReference, |
| int expectedStamp, |
| int newStamp) { |
| ReferenceIntegerPair<V> current = atomicRef.get(); |
| return expectedReference == current.reference && |
| expectedStamp == current.integer && |
| ((newReference == current.reference && |
| newStamp == current.integer) || |
| atomicRef.compareAndSet(current, |
| new ReferenceIntegerPair<V>(newReference, |
| newStamp))); |
| } |
| |
| |
| /** |
| * Unconditionally sets the value of both the reference and stamp. |
| * |
| * @param newReference the new value for the reference |
| * @param newStamp the new value for the stamp |
| */ |
| public void set(V newReference, int newStamp) { |
| ReferenceIntegerPair<V> current = atomicRef.get(); |
| if (newReference != current.reference || newStamp != current.integer) |
| atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp)); |
| } |
| |
| /** |
| * Atomically sets the value of the stamp to the given update value |
| * if the current reference is {@code ==} to the expected |
| * reference. Any given invocation of this operation may fail |
| * (return {@code false}) spuriously, but repeated invocation |
| * when the current value holds the expected value and no other |
| * thread is also attempting to set the value will eventually |
| * succeed. |
| * |
| * @param expectedReference the expected value of the reference |
| * @param newStamp the new value for the stamp |
| * @return true if successful |
| */ |
| public boolean attemptStamp(V expectedReference, int newStamp) { |
| ReferenceIntegerPair<V> current = atomicRef.get(); |
| return expectedReference == current.reference && |
| (newStamp == current.integer || |
| atomicRef.compareAndSet(current, |
| new ReferenceIntegerPair<V>(expectedReference, |
| newStamp))); |
| } |
| } |
