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.

Public Constructor Summary

AtomicStampedReference(V initialRef, int initialStamp) Creates a new AtomicStampedReference with the given initial values.

Public Method Summary

boolean	attemptStamp(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.
boolean	compareAndSet(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.
V	get(int[] stampHolder) Returns the current values of both the reference and the stamp.
V	getReference() Returns the current value of the reference.
int	getStamp() Returns the current value of the stamp.
void	set(V newReference, int newStamp) Unconditionally sets the value of both the reference and stamp.
boolean	weakCompareAndSet(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.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public AtomicStampedReference (V initialRef, int initialStamp)

Creates a new AtomicStampedReference with the given initial values.

Parameters

initialRef	the initial reference
initialStamp	the initial stamp

Public Methods

public boolean attemptStamp (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.

Parameters

expectedReference	the expected value of the reference
newStamp	the new value for the stamp

Returns

• true if successful

public boolean compareAndSet (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.

Parameters

expectedReference	the expected value of the reference
newReference	the new value for the reference
expectedStamp	the expected value of the stamp
newStamp	the new value for the stamp

Returns

• true if successful

public V get (int[] stampHolder)

Returns the current values of both the reference and the stamp. Typical usage is int[1] holder; ref = v.get(holder); .

Parameters

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

Returns

• the current value of the reference

public V getReference ()

Returns the current value of the reference.

Returns

• the current value of the reference

public int getStamp ()

Returns the current value of the stamp.

Returns

• the current value of the stamp

public void set (V newReference, int newStamp)

Unconditionally sets the value of both the reference and stamp.

Parameters

newReference	the new value for the reference
newStamp	the new value for the stamp

public boolean weakCompareAndSet (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.

May fail spuriously and does not provide ordering guarantees, so is only rarely an appropriate alternative to compareAndSet.

Parameters

expectedReference	the expected value of the reference
newReference	the new value for the reference
expectedStamp	the expected value of the stamp
newStamp	the new value for the stamp

Returns

• true if successful