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AtomicMarkableReference.javaAPI DocJava SE 5 API6393Fri Aug 26 14:57:26 BST 2005java.util.concurrent.atomic

AtomicMarkableReference

public class AtomicMarkableReference extends Object
An 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
param
The type of object referred to by this reference

Fields Summary
private final AtomicReference
atomicRef
Constructors Summary
public AtomicMarkableReference(V initialRef, boolean initialMark)
Creates a new AtomicMarkableReference with the given initial values.

param
initialRef the initial reference
param
initialMark the initial mark

        atomicRef = new AtomicReference<ReferenceBooleanPair<V>> (new ReferenceBooleanPair<V>(initialRef, initialMark));
    
Methods Summary
public booleanattemptMark(V expectedReference, boolean newMark)
Atomically sets the value of the mark to the given update value if the current reference is == to the expected reference. Any given invocation of this operation may fail (return 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

        ReferenceBooleanPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            (newMark == current.bit ||
             atomicRef.compareAndSet
             (current, new ReferenceBooleanPair<V>(expectedReference,
                                                newMark)));
    
public booleancompareAndSet(V expectedReference, V newReference, boolean expectedMark, boolean newMark)
Atomically sets the value of both the reference and mark to the given update values if the current reference is == 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

        ReferenceBooleanPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            expectedMark == current.bit &&
            ((newReference == current.reference && newMark == current.bit) ||
             atomicRef.compareAndSet(current,
                                     new ReferenceBooleanPair<V>(newReference,
                                                              newMark)));
    
public Vget(boolean[] markHolder)
Returns the current values of both the reference and the mark. Typical usage is boolean[1] holder; ref = v.get(holder); .

param
markHolder an array of size of at least one. On return, markholder[0] will hold the value of the mark.
return
the current value of the reference

        ReferenceBooleanPair<V> p = atomicRef.get();
        markHolder[0] = p.bit;
        return p.reference;
    
public VgetReference()
Returns the current value of the reference.

return
the current value of the reference

        return atomicRef.get().reference;
    
public booleanisMarked()
Returns the current value of the mark.

return
the current value of the mark

        return atomicRef.get().bit;
    
public voidset(V newReference, boolean 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

        ReferenceBooleanPair current = atomicRef.get();
        if (newReference != current.reference || newMark != current.bit)
            atomicRef.set(new ReferenceBooleanPair<V>(newReference, newMark));
    
public booleanweakCompareAndSet(V expectedReference, V newReference, boolean expectedMark, boolean newMark)
Atomically sets the value of both the reference and mark to the given update values if the current reference is == to the expected reference and the current mark is equal to the expected mark. Any given invocation of this operation may fail (return 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
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

        ReferenceBooleanPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            expectedMark == current.bit &&
            ((newReference == current.reference && newMark == current.bit) ||
             atomicRef.weakCompareAndSet(current,
                                     new ReferenceBooleanPair<V>(newReference,
                                                              newMark)));