edu.emory.mathcs.backport.java.util.concurrent.atomic
Class AtomicStampedReference

java.lang.Object
  edu.emory.mathcs.backport.java.util.concurrent.atomic.AtomicStampedReference

public class AtomicStampedReference

extends java.lang.Object

An 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

Constructor Summary

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

Method Summary

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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AtomicStampedReference

public AtomicStampedReference(java.lang.Object initialRef,
                              int initialStamp)

Creates a new with the given initial values.

Parameters:

initialRef - the initial reference

initialStamp - the initial stamp

Method Detail

getReference

public java.lang.Object getReference()

Returns the current value of the reference.

Returns:

the current value of the reference

getStamp

public int getStamp()

Returns the current value of the stamp.

Returns:

the current value of the stamp

get

public java.lang.Object get(int[] stampHolder)

Returns the current values of both the reference and the stamp. Typical usage is .

Parameters:

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

Returns:

the current value of the reference

weakCompareAndSet

public boolean weakCompareAndSet(java.lang.Object expectedReference,
                                 java.lang.Object 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 .

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

compareAndSet

public boolean compareAndSet(java.lang.Object expectedReference,
                             java.lang.Object 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

set

public void set(java.lang.Object 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

attemptStamp

public boolean attemptStamp(java.lang.Object 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 ) 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