java.util.concurrent.atomic

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.

    Since:
    1.5
    • Constructor Summary

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

        

    • Method Summary

      Methods 
      Modifier and Type Method and 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.

        

    • 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

Traduction non disponible

Les API Java ne sont pas encore traduites en français sur l'infobrol. Seule la version anglaise est disponible pour l'instant.

 

Document créé le 21/09/2006, dernière modification le 29/10/2018
Source du document imprimé : https://www.gaudry.be/java-api-rf-java/util/concurrent/atomic/atomicreferencefieldupdater.html

L'infobrol est un site personnel dont le contenu n'engage que moi. Le texte est mis à disposition sous licence CreativeCommons(BY-NC-SA). Plus d'info sur les conditions d'utilisation et sur l'auteur.

Références

  1. Consulter le document html Langue du document :fr Manuel PHP : https://docs.oracle.com, AtomicReferenceFieldUpdater

Ces références et liens indiquent des documents consultés lors de la rédaction de cette page, ou qui peuvent apporter un complément d'information, mais les auteurs de ces sources ne peuvent être tenus responsables du contenu de cette page.
L'auteur de ce site est seul responsable de la manière dont sont présentés ici les différents concepts, et des libertés qui sont prises avec les ouvrages de référence. N'oubliez pas que vous devez croiser les informations de sources multiples afin de diminuer les risques d'erreurs.