Android
java.util.concurrent.atomic
public abstract class

java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T, V>

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 and volatile semantics only with respect to other invocations of compareAndSet and set.

Summary

Protected Constructors

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

Public Methods

abstract          boolean  compareAndSet(T obj, V expect, V update)
Atomically set the value of the field of the given object managed by this Updater to the given updated value if the current value == the expected value.
abstract          get(T obj)
Get the current value held in the field by the given object.
          getAndSet(T obj, V newValue)
Set to the given value and return the old value.
      static  <U, W>  AtomicReferenceFieldUpdater<U, W>  newUpdater(Class<U> tclass, Class<W> vclass, String fieldName)
Creates an updater for objects with the given field.
abstract          void  set(T obj, V newValue)
Set the field of the given object managed by this updater.
abstract          boolean  weakCompareAndSet(T obj, V expect, V update)
Atomically set the value of the field of the given object managed by this Updater to the given updated value if the current value == the expected value.
Methods inherited from class java.lang.Object

Details

Protected Constructors

protected AtomicReferenceFieldUpdater()

Protected do-nothing constructor for use by subclasses.

Public Methods

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

Atomically set the value of 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)

Get the current value held in the field by the given object.

Parameters

obj An object whose field to get

Returns

  • the current value

public V getAndSet(T obj, V newValue)

Set to the given value and return 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)

Creates 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)

Set the field of the given object managed by this updater. 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)

Atomically set the value of 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, and may fail spuriously.

Parameters

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

Returns

  • true if successful.
Copyright 2007 Google Inc. Build 0.9_r1-98467 - 14 Aug 2008 18:56