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AtomicStampedReference.javaAPI DocJava SE 5 API6520Fri Aug 26 14:57:26 BST 2005java.util.concurrent.atomic

AtomicStampedReference

public class AtomicStampedReference extends Object
An 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

Fields Summary
private final AtomicReference
atomicRef
Constructors Summary
public AtomicStampedReference(V initialRef, int initialStamp)
Creates a new AtomicStampedReference with the given initial values.

param
initialRef the initial reference
param
initialStamp the initial stamp

        atomicRef = new AtomicReference<ReferenceIntegerPair<V>>
            (new ReferenceIntegerPair<V>(initialRef, initialStamp));
    
Methods Summary
public booleanattemptStamp(V expectedReference, int newStamp)
Atomically sets the value of the stamp 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
newStamp the new value for the stamp
return
true if successful

        ReferenceIntegerPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            (newStamp == current.integer ||
             atomicRef.compareAndSet(current,
                                     new ReferenceIntegerPair<V>(expectedReference,
                                                              newStamp)));
    
public booleancompareAndSet(V expectedReference, V newReference, int expectedStamp, int newStamp)
Atomically sets the value of both the reference and stamp to the given update values if the current reference is == 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

        ReferenceIntegerPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            expectedStamp == current.integer &&
            ((newReference == current.reference &&
              newStamp == current.integer) ||
             atomicRef.compareAndSet(current,
                                     new ReferenceIntegerPair<V>(newReference,
                                                              newStamp)));
    
public Vget(int[] stampHolder)
Returns the current values of both the reference and the stamp. Typical usage is int[1] holder; ref = v.get(holder); .

param
stampHolder an array of size of at least one. On return, stampholder[0] will hold the value of the stamp.
return
the current value of the reference

        ReferenceIntegerPair<V> p = atomicRef.get();
        stampHolder[0] = p.integer;
        return p.reference;
    
public VgetReference()
Returns the current value of the reference.

return
the current value of the reference

        return atomicRef.get().reference;
    
public intgetStamp()
Returns the current value of the stamp.

return
the current value of the stamp

        return atomicRef.get().integer;
    
public voidset(V newReference, int 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

        ReferenceIntegerPair current = atomicRef.get();
        if (newReference != current.reference || newStamp != current.integer)
            atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp));
    
public booleanweakCompareAndSet(V expectedReference, V newReference, int expectedStamp, int newStamp)
Atomically sets the value of both the reference and stamp to the given update values if the current reference is == to the expected reference and the current stamp is equal to the expected stamp. 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
expectedStamp the expected value of the stamp
param
newStamp the new value for the stamp
return
true if successful

        ReferenceIntegerPair current = atomicRef.get();
        return  expectedReference == current.reference &&
            expectedStamp == current.integer &&
            ((newReference == current.reference &&
              newStamp == current.integer) ||
             atomicRef.weakCompareAndSet(current,
                                     new ReferenceIntegerPair<V>(newReference,
                                                              newStamp)));