/*
* 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
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/*
* 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;
/** {@collect.stats}
* {@description.open}
* An {@code AtomicMarkableReference} maintains an object reference
* along with a mark bit, that can be updated atomically.
* <p>
* <p> Implementation note. This implementation maintains markable
* references by creating internal objects representing "boxed"
* [reference, boolean] pairs.
* {@description.close}
*
* @since 1.5
* @author Doug Lea
* @param <V> The type of object referred to by this reference
*/
public class AtomicMarkableReference<V> {
private static class ReferenceBooleanPair<T> {
private final T reference;
private final boolean bit;
ReferenceBooleanPair(T r, boolean i) {
reference = r; bit = i;
}
}
private final AtomicReference<ReferenceBooleanPair<V>> atomicRef;
/** {@collect.stats}
* {@description.open}
* Creates a new {@code AtomicMarkableReference} with the given
* initial values.
* {@description.close}
*
* @param initialRef the initial reference
* @param initialMark the initial mark
*/
public AtomicMarkableReference(V initialRef, boolean initialMark) {
atomicRef = new AtomicReference<ReferenceBooleanPair<V>> (new ReferenceBooleanPair<V>(initialRef, initialMark));
}
/** {@collect.stats}
* {@description.open}
* Returns the current value of the reference.
* {@description.close}
*
* @return the current value of the reference
*/
public V getReference() {
return atomicRef.get().reference;
}
/** {@collect.stats}
* {@description.open}
* Returns the current value of the mark.
* {@description.close}
*
* @return the current value of the mark
*/
public boolean isMarked() {
return atomicRef.get().bit;
}
/** {@collect.stats}
* {@description.open}
* Returns the current values of both the reference and the mark.
* Typical usage is {@code boolean[1] holder; ref = v.get(holder); }.
* {@description.close}
*
* @param markHolder an array of size of at least one. On return,
* {@code markholder[0]} will hold the value of the mark.
* @return the current value of the reference
*/
public V get(boolean[] markHolder) {
ReferenceBooleanPair<V> p = atomicRef.get();
markHolder[0] = p.bit;
return p.reference;
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the value of both the reference and mark
* to the given update values if the
* current reference is {@code ==} to the expected reference
* and the current mark is equal to the expected mark.
*
* <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}.
* {@description.close}
*
* @param expectedReference the expected value of the reference
* @param newReference the new value for the reference
* @param expectedMark the expected value of the mark
* @param newMark the new value for the mark
* @return true if successful
*/
public boolean weakCompareAndSet(V expectedReference,
V newReference,
boolean expectedMark,
boolean newMark) {
ReferenceBooleanPair<V> current = atomicRef.get();
return expectedReference == current.reference &&
expectedMark == current.bit &&
((newReference == current.reference && newMark == current.bit) ||
atomicRef.weakCompareAndSet(current,
new ReferenceBooleanPair<V>(newReference,
newMark)));
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the value of both the reference and mark
* to the given update values if the
* current reference is {@code ==} to the expected reference
* and the current mark is equal to the expected mark.
* {@description.close}
*
* @param expectedReference the expected value of the reference
* @param newReference the new value for the reference
* @param expectedMark the expected value of the mark
* @param newMark the new value for the mark
* @return true if successful
*/
public boolean compareAndSet(V expectedReference,
V newReference,
boolean expectedMark,
boolean newMark) {
ReferenceBooleanPair<V> current = atomicRef.get();
return expectedReference == current.reference &&
expectedMark == current.bit &&
((newReference == current.reference && newMark == current.bit) ||
atomicRef.compareAndSet(current,
new ReferenceBooleanPair<V>(newReference,
newMark)));
}
/** {@collect.stats}
* {@description.open}
* Unconditionally sets the value of both the reference and mark.
* {@description.close}
*
* @param newReference the new value for the reference
* @param newMark the new value for the mark
*/
public void set(V newReference, boolean newMark) {
ReferenceBooleanPair<V> current = atomicRef.get();
if (newReference != current.reference || newMark != current.bit)
atomicRef.set(new ReferenceBooleanPair<V>(newReference, newMark));
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the value of the mark 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.
* {@description.close}
*
* @param expectedReference the expected value of the reference
* @param newMark the new value for the mark
* @return true if successful
*/
public boolean attemptMark(V expectedReference, boolean newMark) {
ReferenceBooleanPair<V> current = atomicRef.get();
return expectedReference == current.reference &&
(newMark == current.bit ||
atomicRef.compareAndSet
(current, new ReferenceBooleanPair<V>(expectedReference,
newMark)));
}
}