AtomicMarkableReference

AI-generated Key Takeaways

• AtomicMarkableReference atomically manages an object reference and a boolean mark.

• It provides methods to atomically update both the reference and the mark, or just the mark.

• compareAndSet and weakCompareAndSet conditionally update the reference and mark based on expected values.

• get retrieves the current reference and mark, while getReference and isMarked access them individually.

• set unconditionally updates both the reference and mark to new values.

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.

Public Constructor Summary

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

Public Method Summary

boolean	attemptMark(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.
boolean	compareAndSet(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.
V	get(boolean[] markHolder) Returns the current values of both the reference and the mark.
V	getReference() Returns the current value of the reference.
boolean	isMarked() Returns the current value of the mark.
void	set(V newReference, boolean newMark) Unconditionally sets the value of both the reference and mark.
boolean	weakCompareAndSet(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.

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 AtomicMarkableReference (V initialRef, boolean initialMark)

Creates a new AtomicMarkableReference with the given initial values.

Parameters

initialRef	the initial reference
initialMark	the initial mark

Public Methods

public boolean attemptMark (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.

Parameters

expectedReference	the expected value of the reference
newMark	the new value for the mark

Returns

• true if successful

public boolean compareAndSet (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.

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

public V 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

public V getReference ()

Returns the current value of the reference.

Returns

• the current value of the reference

public boolean isMarked ()

Returns the current value of the mark.

Returns

• the current value of the mark

public void set (V 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

public boolean weakCompareAndSet (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.

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
expectedMark	the expected value of the mark
newMark	the new value for the mark

Returns

• true if successful