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 non-static volatile reference fields of designated classes, providing a subset of the functionality of class VarHandle that should be used instead. This class may be used 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 final 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
}
However, it is preferable to use VarHandle: 
import java.lang.invoke.VarHandle;
import java.lang.invoke.MethodHandles;
class Node {
 private volatile Node left, right;
 private static final VarHandle LEFT, RIGHT;
 Node getLeft() { return left; }
 boolean compareAndSetLeft(Node expect, Node update) {
   return LEFT.compareAndSet(this, expect, update);
 }
 // ... and so on
 static { try {
   MethodHandles.Lookup l = MethodHandles.lookup();
   LEFT  = l.findVarHandle(Node.class, "left", Node.class);
   RIGHT = l.findVarHandle(Node.class, "right", Node.class);
  } catch (ReflectiveOperationException e) {
    throw new ExceptionInInitializerError(e);
}}}

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(Class, Class, String) will result in a ClassCastException being thrown.

Since:
1.5

  • Constructor Summary

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

  • Method Summary

    Modifier and Type
    Method
    Description
    final V
    accumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction)
    Atomically updates (with memory effects as specified by VarHandle.compareAndSet(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.
    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)
    Returns the current value held in the field of the given object managed by this updater.
    final V
    getAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction)
    Atomically updates (with memory effects as specified by VarHandle.compareAndSet(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.
    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.
    final V
    getAndUpdate(T obj, UnaryOperator<V> updateFunction)
    Atomically updates (with memory effects as specified by VarHandle.compareAndSet(Object...)) the field of the given object managed by this updater with the results of applying the given function, returning the previous 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.
    final V
    updateAndGet(T obj, UnaryOperator<V> updateFunction)
    Atomically updates (with memory effects as specified by VarHandle.compareAndSet(Object...)) the field of the given object managed by this updater with the results of applying the given function, returning the 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 declared in class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Creates and returns a copy of this object.
    boolean
    equals(Object obj)
    Indicates whether some other object is "equal to" this one.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    Finalization is deprecated and subject to removal in a future release.
    final Class<?>
    getClass()
    Returns the runtime class of this Object.
    int
    hashCode()
    Returns a hash code value for this object.
    final void
    notify()
    Wakes up a single thread that is waiting on this object's monitor.
    final void
    notifyAll()
    Wakes up all threads that are waiting on this object's monitor.
    String
    toString()
    Returns a string representation of the object.
    final void
    wait()
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
    final void
    wait(long timeoutMillis)
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
    final void
    wait(long timeoutMillis, int nanos)
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

  • 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.
      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.

      This operation 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(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(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(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(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