diff -r fd16c54261b3 -r 90ce3da70b43 jdk/src/share/classes/java/util/concurrent/atomic/AtomicStampedReference.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/jdk/src/share/classes/java/util/concurrent/atomic/AtomicStampedReference.java Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,196 @@ +/* + * 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. Sun designates this + * particular file as subject to the "Classpath" exception as provided + * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.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. + * + *

Implementation note. This implementation maintains stamped + * references by creating internal objects representing "boxed" + * [reference, integer] pairs. + * + * @since 1.5 + * @author Doug Lea + * @param The type of object referred to by this reference + */ +public class AtomicStampedReference { + + private static class ReferenceIntegerPair { + private final T reference; + private final int integer; + ReferenceIntegerPair(T r, int i) { + reference = r; integer = i; + } + } + + private final AtomicReference> 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> + (new ReferenceIntegerPair(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 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. + * + *

May fail spuriously + * 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 current = atomicRef.get(); + return expectedReference == current.reference && + expectedStamp == current.integer && + ((newReference == current.reference && + newStamp == current.integer) || + atomicRef.weakCompareAndSet(current, + new ReferenceIntegerPair(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 current = atomicRef.get(); + return expectedReference == current.reference && + expectedStamp == current.integer && + ((newReference == current.reference && + newStamp == current.integer) || + atomicRef.compareAndSet(current, + new ReferenceIntegerPair(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 current = atomicRef.get(); + if (newReference != current.reference || newStamp != current.integer) + atomicRef.set(new ReferenceIntegerPair(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 current = atomicRef.get(); + return expectedReference == current.reference && + (newStamp == current.integer || + atomicRef.compareAndSet(current, + new ReferenceIntegerPair(expectedReference, + newStamp))); + } +}