Package java.util.concurrent.atomic

Class AtomicReferenceFieldUpdater<T,​V>

java.lang.Object
java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T,​V>
Type Parameters:
T - The type of the object holding the updatable field
V - The type of the field
public abstract class AtomicReferenceFieldUpdater<T,​V>
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.

Since:
1.5
Author:
Doug Lea

  • Constructor Summary

    Constructors
    Modifier Constructor Description
    protected AtomicReferenceFieldUpdater()
    Protected do-nothing constructor for use by subclasses.

  • Method Summary

    Modifier and Type Method Description
    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.
    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.
    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.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • AtomicReferenceFieldUpdater

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

  • Method Details

    • newUpdater

      public 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. 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, or the field is inaccessible to the caller according to Java language access control

    • compareAndSet

      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

    • weakCompareAndSet

      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

    • set

      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

    • lazySet

      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
      Since:
      1.6

    • get

      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

    • getAndSet

      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