edu.emory.mathcs.backport.java.util.concurrent.atomic.AtomicMarkableReference Maven / Gradle / Ivy
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/*
* 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 edu.emory.mathcs.backport.java.util.concurrent.atomic;
/**
* An {@code AtomicMarkableReference} maintains an object reference
* along with a mark bit, that can be updated atomically.
*
*
Implementation note. This implementation maintains markable
* references by creating internal objects representing "boxed"
* [reference, boolean] pairs.
*
* @since 1.5
* @author Doug Lea
*/
public class AtomicMarkableReference {
private static class ReferenceBooleanPair {
private final Object reference;
private final boolean bit;
ReferenceBooleanPair(Object r, boolean i) {
reference = r; bit = i;
}
}
private final AtomicReference atomicRef;
/**
* Creates a new {@code AtomicMarkableReference} with the given
* initial values.
*
* @param initialRef the initial reference
* @param initialMark the initial mark
*/
public AtomicMarkableReference(Object initialRef, boolean initialMark) {
atomicRef = new AtomicReference(new ReferenceBooleanPair(initialRef, initialMark));
}
private ReferenceBooleanPair getPair() {
return (ReferenceBooleanPair)atomicRef.get();
}
/**
* Returns the current value of the reference.
*
* @return the current value of the reference
*/
public Object getReference() {
return getPair().reference;
}
/**
* Returns the current value of the mark.
*
* @return the current value of the mark
*/
public boolean isMarked() {
return getPair().bit;
}
/**
* Returns the current values of both the reference and the mark.
* Typical usage is {@code boolean[1] holder; ref = v.get(holder); }.
*
* @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 Object get(boolean[] markHolder) {
ReferenceBooleanPair p = getPair();
markHolder[0] = p.bit;
return p.reference;
}
/**
* 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.
*
*
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 expectedMark the expected value of the mark
* @param newMark the new value for the mark
* @return true if successful
*/
public boolean weakCompareAndSet(Object expectedReference,
Object newReference,
boolean expectedMark,
boolean newMark) {
ReferenceBooleanPair current = getPair();
return expectedReference == current.reference &&
expectedMark == current.bit &&
((newReference == current.reference && newMark == current.bit) ||
atomicRef.weakCompareAndSet(current,
new ReferenceBooleanPair(newReference,
newMark)));
}
/**
* 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.
*
* @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(Object expectedReference,
Object newReference,
boolean expectedMark,
boolean newMark) {
ReferenceBooleanPair current = getPair();
return expectedReference == current.reference &&
expectedMark == current.bit &&
((newReference == current.reference && newMark == current.bit) ||
atomicRef.compareAndSet(current,
new ReferenceBooleanPair(newReference,
newMark)));
}
/**
* Unconditionally sets the value of both the reference and mark.
*
* @param newReference the new value for the reference
* @param newMark the new value for the mark
*/
public void set(Object newReference, boolean newMark) {
ReferenceBooleanPair current = getPair();
if (newReference != current.reference || newMark != current.bit)
atomicRef.set(new ReferenceBooleanPair(newReference, newMark));
}
/**
* 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.
*
* @param expectedReference the expected value of the reference
* @param newMark the new value for the mark
* @return true if successful
*/
public boolean attemptMark(Object expectedReference, boolean newMark) {
ReferenceBooleanPair current = getPair();
return expectedReference == current.reference &&
(newMark == current.bit ||
atomicRef.compareAndSet
(current, new ReferenceBooleanPair(expectedReference,
newMark)));
}
}