AtomicReferenceFieldUpdaterpublic abstract class AtomicReferenceFieldUpdater 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 and volatile
semantics only with respect to other invocations of
compareAndSet and set. |
| Constructors Summary |
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protected AtomicReferenceFieldUpdater()Protected do-nothing constructor for use by subclasses.
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| Methods Summary |
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| public abstract boolean | compareAndSet(T obj, V expect, V update)Atomically set the value of 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.
| | public abstract V | get(T obj)Get the current value held in the field by the given object.
| | public V | getAndSet(T obj, V newValue)Set to the given value and return the old value.
for (;;) {
V current = get(obj);
if (compareAndSet(obj, current, newValue))
return current;
}
| | public static java.util.concurrent.atomic.AtomicReferenceFieldUpdater | newUpdater(java.lang.Class tclass, java.lang.Class vclass, java.lang.String fieldName)Creates an updater for objects with the given field. The Class
arguments are needed to check that reflective types and generic
types match.
// Currently rely on standard intrinsics implementation
return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass,
vclass,
fieldName);
| | public abstract void | set(T obj, V newValue)Set the field of the given object managed by this updater. This
operation is guaranteed to act as a volatile store with respect
to subsequent invocations of compareAndSet.
| | public abstract boolean | weakCompareAndSet(T obj, V expect, V update)Atomically set the value of 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, and may fail spuriously.
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