AtomicReferenceFieldUpdater

public abstract class AtomicReferenceFieldUpdater extends Object

A reflection-based utility that enables atomic updates to designated volatile reference fields of designated classes. This class is designed for use in atomic data structures in which several reference fields of the same node are independently subject to atomic updates. For example, a tree node might be declared as

 class Node {
   private volatile Node left, right;

   private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
     AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
   private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
     AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");

   Node getLeft() { return left; }
   boolean compareAndSetLeft(Node expect, Node update) {
     return leftUpdater.compareAndSet(this, expect, update);
   }
   // ... and so on
 }

Note that the guarantees of the compareAndSet method in this class are weaker than in other atomic classes. Because this class cannot ensure that all uses of the field are appropriate for purposes of atomic access, it can guarantee atomicity only with respect to other invocations of compareAndSet and set on the same updater.

Protected Constructor Summary

AtomicReferenceFieldUpdater() Protected do-nothing constructor for use by subclasses.

Public Method Summary

final V	accumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction) Atomically updates the field of the given object managed by this updater with the results of applying the given function to the current and given values, returning the updated value.
abstract boolean	compareAndSet(T obj, V expect, V update) Atomically sets the field of the given object managed by this updater to the given updated value if the current value == the expected value.
abstract V	get(T obj) Gets the current value held in the field of the given object managed by this updater.
final V	getAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction) Atomically updates the field of the given object managed by this updater with the results of applying the given function to the current and given values, returning the previous value.
V	getAndSet(T obj, V newValue) Atomically sets the field of the given object managed by this updater to the given value and returns the old value.
final V	getAndUpdate(T obj, UnaryOperator<V> updateFunction) Atomically updates the field of the given object managed by this updater with the results of applying the given function, returning the previous value.
abstract void	lazySet(T obj, V newValue) Eventually sets the field of the given object managed by this updater to the given updated value.
static <U, W> AtomicReferenceFieldUpdater<U, W>	newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) Creates and returns an updater for objects with the given field.
abstract void	set(T obj, V newValue) Sets the field of the given object managed by this updater to the given updated value.
final V	updateAndGet(T obj, UnaryOperator<V> updateFunction) Atomically updates the field of the given object managed by this updater with the results of applying the given function, returning the updated value.
abstract boolean	weakCompareAndSet(T obj, V expect, V update) Atomically sets the field of the given object managed by this updater to the given updated value if the current value == the expected value.

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.

Protected Constructors

protected AtomicReferenceFieldUpdater ()

Protected do-nothing constructor for use by subclasses.

Public Methods

public final V accumulateAndGet (T obj, V x, BinaryOperator<V> accumulatorFunction)

Atomically updates the field of the given object managed by this updater with the results of applying the given function to the current and given values, returning the updated value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value as its first argument, and the given update as the second argument.

Parameters

obj	An object whose field to get and set
x	the update value
accumulatorFunction	a side-effect-free function of two arguments

Returns

• the updated value

public abstract boolean compareAndSet (T obj, V expect, V update)

Atomically sets the field of the given object managed by this updater to the given updated value if the current value == the expected value. This method is guaranteed to be atomic with respect to other calls to compareAndSet and set, but not necessarily with respect to other changes in the field.

Parameters

obj	An object whose field to conditionally set
expect	the expected value
update	the new value

Returns

• true if successful

public abstract V get (T obj)

Gets the current value held in the field of the given object managed by this updater.

Parameters

obj	An object whose field to get

Returns

• the current value

public final V getAndAccumulate (T obj, V x, BinaryOperator<V> accumulatorFunction)

Atomically updates the field of the given object managed by this updater with the results of applying the given function to the current and given values, returning the previous value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value as its first argument, and the given update as the second argument.

Parameters

obj	An object whose field to get and set
x	the update value
accumulatorFunction	a side-effect-free function of two arguments

Returns

• the previous value

public V getAndSet (T obj, V newValue)

Atomically sets the field of the given object managed by this updater to the given value and returns the old value.

Parameters

obj	An object whose field to get and set
newValue	the new value

Returns

• the previous value

public final V getAndUpdate (T obj, UnaryOperator<V> updateFunction)

Atomically updates the field of the given object managed by this updater with the results of applying the given function, returning the previous value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads.

Parameters

obj	An object whose field to get and set
updateFunction	a side-effect-free function

Returns

• the previous value

public abstract void lazySet (T obj, V newValue)

Eventually sets the field of the given object managed by this updater to the given updated value.

Parameters

obj	An object whose field to set
newValue	the new value

public static AtomicReferenceFieldUpdater<U, W> newUpdater (Class<U> tclass, Class<W> vclass, String fieldName)

Creates and returns an updater for objects with the given field. The Class arguments are needed to check that reflective types and generic types match.

Parameters

tclass	the class of the objects holding the field
vclass	the class of the field
fieldName	the name of the field to be updated

Returns

• the updater

Throws

ClassCastException	if the field is of the wrong type
IllegalArgumentException	if the field is not volatile
RuntimeException	with a nested reflection-based exception if the class does not hold field or is the wrong type, or the field is inaccessible to the caller according to Java language access control

public abstract void set (T obj, V newValue)

Sets the field of the given object managed by this updater to the given updated value. This operation is guaranteed to act as a volatile store with respect to subsequent invocations of compareAndSet.

Parameters

obj	An object whose field to set
newValue	the new value

public final V updateAndGet (T obj, UnaryOperator<V> updateFunction)

Atomically updates the field of the given object managed by this updater with the results of applying the given function, returning the updated value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads.

Parameters

obj	An object whose field to get and set
updateFunction	a side-effect-free function

Returns

• the updated value

public abstract boolean weakCompareAndSet (T obj, V expect, V update)

Atomically sets the field of the given object managed by this updater to the given updated value if the current value == the expected value. This method is guaranteed to be atomic with respect to other calls to compareAndSet and set, but not necessarily with respect to other changes in the field.

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

Parameters

obj	An object whose field to conditionally set
expect	the expected value
update	the new value

Returns

• true if successful