org.compass.core.util.backport.java.util.concurrent.atomic
Class AtomicMarkableReference

java.lang.Object
  org.compass.core.util.backport.java.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

Constructor Summary

AtomicMarkableReference(Object initialRef, boolean initialMark)
Creates a new AtomicMarkableReference with the given initial values.

Method Summary

boolean	attemptMark(Object expectedReference, boolean newMark) Atomically sets the value of the mark to the given update value if the current reference is == to the expected reference.
boolean	compareAndSet(Object expectedReference, Object 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.
Object	get(boolean[] markHolder) Returns the current values of both the reference and the mark.
Object	getReference() Returns the current value of the reference.
boolean	isMarked() Returns the current value of the mark.
void	set(Object newReference, boolean newMark) Unconditionally sets the value of both the reference and mark.
boolean	weakCompareAndSet(Object expectedReference, Object 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.

Methods inherited from class java.lang.Object

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

Constructor Detail

AtomicMarkableReference

public AtomicMarkableReference(Object initialRef,
                               boolean initialMark)

Creates a new AtomicMarkableReference with the given initial values.

Parameters:

initialRef - the initial reference

initialMark - the initial mark

Method Detail

getReference

public Object getReference()

Returns the current value of the reference.

Returns:

the current value of the reference

isMarked

public boolean isMarked()

Returns the current value of the mark.

Returns:

the current value of the mark

get

public Object get(boolean[] markHolder)

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

Parameters:

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

Returns:

the current value of the reference

weakCompareAndSet

public boolean weakCompareAndSet(Object expectedReference,
                                 Object 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.

Parameters:

expectedReference - the expected value of the reference

newReference - the new value for the reference

expectedMark - the expected value of the mark

newMark - the new value for the mark

Returns:

true if successful

compareAndSet

public boolean compareAndSet(Object expectedReference,
                             Object 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.

Parameters:

expectedReference - the expected value of the reference

newReference - the new value for the reference

expectedMark - the expected value of the mark

newMark - the new value for the mark

Returns:

true if successful

set

public void set(Object newReference,
                boolean newMark)

Unconditionally sets the value of both the reference and mark.

Parameters:

newReference - the new value for the reference

newMark - the new value for the mark

attemptMark

public boolean attemptMark(Object 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.

Parameters:

expectedReference - the expected value of the reference

newMark - the new value for the mark

Returns:

true if successful