Module java.base

Class 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.

    Object arguments for parameters of type T that are not instances of the class passed to newUpdater(java.lang.Class<U>, java.lang.Class<W>, java.lang.String) will result in a ClassCastException being thrown.

    Since:
    1.5
    Author:
    Doug Lea
    • 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.
        Type Parameters:
        U - the type of instances of tclass
        W - the type of instances of vclass
        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:
        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
      • 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)
        Returns 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
      • getAndUpdate

        public final V getAndUpdate​(T obj,
                                    UnaryOperator<V> updateFunction)
        Atomically updates (with memory effects as specified by VarHandle.compareAndSet(java.lang.Object...)) 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 - An object whose field to get and set
        updateFunction - a side-effect-free function
        Returns:
        the previous value
        Since:
        1.8
      • updateAndGet

        public final V updateAndGet​(T obj,
                                    UnaryOperator<V> updateFunction)
        Atomically updates (with memory effects as specified by VarHandle.compareAndSet(java.lang.Object...)) 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 - An object whose field to get and set
        updateFunction - a side-effect-free function
        Returns:
        the updated value
        Since:
        1.8
      • getAndAccumulate

        public final V getAndAccumulate​(T obj,
                                        V x,
                                        BinaryOperator<V> accumulatorFunction)
        Atomically updates (with memory effects as specified by VarHandle.compareAndSet(java.lang.Object...)) 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 - An object whose field to get and set
        x - the update value
        accumulatorFunction - a side-effect-free function of two arguments
        Returns:
        the previous value
        Since:
        1.8
      • accumulateAndGet

        public final V accumulateAndGet​(T obj,
                                        V x,
                                        BinaryOperator<V> accumulatorFunction)
        Atomically updates (with memory effects as specified by VarHandle.compareAndSet(java.lang.Object...)) 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 - An object whose field to get and set
        x - the update value
        accumulatorFunction - a side-effect-free function of two arguments
        Returns:
        the updated value
        Since:
        1.8