public abstract class

AtomicReferenceFieldUpdater

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

Class Overview

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
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.
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.
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.
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.
[Expand]
Inherited Methods
From class java.lang.Object

Protected Constructors

protected AtomicReferenceFieldUpdater ()

Since: API Level 1

Protected do-nothing constructor for use by subclasses.

Public Methods

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

Since: API Level 1

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)

Since: API Level 1

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 V getAndSet (T obj, V newValue)

Since: API Level 1

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

Since: API Level 1

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
IllegalArgumentException if the field is not a volatile reference type.
RuntimeException with a nested reflection-based exception if the class does not hold field or is the wrong type.

public abstract void set (T obj, V newValue)

Since: API Level 1

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

Since: API Level 1

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.