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AtomicReferenceFieldUpdater

public abstract class AtomicReferenceFieldUpdater
extends Object

java.lang.Object
   ↳ java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T, V>


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.

Summary

Protected constructors

AtomicReferenceFieldUpdater()

Protected do-nothing constructor for use by subclasses.

Public methods

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 methods

From class java.lang.Object

Protected constructors

AtomicReferenceFieldUpdater

added in API level 1
AtomicReferenceFieldUpdater ()

Protected do-nothing constructor for use by subclasses.

Public methods

accumulateAndGet

added in API level 24
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 T: An object whose field to get and set

x V: the update value

accumulatorFunction BinaryOperator: a side-effect-free function of two arguments

Returns
V the updated value

compareAndSet

added in API level 1
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 T: An object whose field to conditionally set

expect V: the expected value

update V: the new value

Returns
boolean true if successful

get

added in API level 1
V get (T obj)

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

Parameters
obj T: An object whose field to get

Returns
V the current value

getAndAccumulate

added in API level 24
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 T: An object whose field to get and set

x V: the update value

accumulatorFunction BinaryOperator: a side-effect-free function of two arguments

Returns
V the previous value

getAndSet

added in API level 1
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 T: An object whose field to get and set

newValue V: the new value

Returns
V the previous value

getAndUpdate

added in API level 24
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 T: An object whose field to get and set

updateFunction UnaryOperator: a side-effect-free function

Returns
V the previous value

lazySet

added in API level 9
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 T: An object whose field to set

newValue V: the new value

newUpdater

added in API level 1
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 Class: the class of the objects holding the field

vclass Class: the class of the field

fieldName String: the name of the field to be updated

Returns
AtomicReferenceFieldUpdater<U, W> 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

set

added in API level 1
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 T: An object whose field to set

newValue V: the new value

updateAndGet

added in API level 24
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 T: An object whose field to get and set

updateFunction UnaryOperator: a side-effect-free function

Returns
V the updated value

weakCompareAndSet

added in API level 1
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 T: An object whose field to conditionally set

expect V: the expected value

update V: the new value

Returns
boolean true if successful

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