java.util.concurrent.atomic

Class AtomicReferenceFieldUpdater<- ;T,V>

Contents
  • 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

    • Constructor Detail

      • AtomicReferenceFieldUpdater

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

    • Method Detail

      • 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.

      • 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

Document created the 11/06/2005, last modified the 04/03/2020
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