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

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 thread