java.util.concurrent.atomic
Class AtomicReferenceFieldUpdater<T,V>
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.
static | W> AtomicReferenceFieldUpdater newUpdater(Class tclass, Class vclass, String fieldName) - Creates and returns an updater for objects with the given field.
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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.
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abstract V | get(T obj) - Gets the current value held in the field of the given object managed
by this updater.
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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.
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abstract void | lazySet(T obj, V newValue) - Eventually sets the field of the given object managed by this
updater to the given updated value.
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abstract void | set(T obj, V newValue) - Sets the field of the given object managed by this updater to the
given updated value.
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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.
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clone , equals , extends Object> getClass , finalize , hashCode , notify , notifyAll , toString , wait , wait , wait |
W> AtomicReferenceFieldUpdater newUpdater
public static W> AtomicReferenceFieldUpdater newUpdater(Class tclass,
Class 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.
tclass
- the class of the objects holding the field.vclass
- the class of the fieldfieldName
- the name of the field to be updated.
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.
obj
- An object whose field to conditionally setexpect
- the expected valueupdate
- the new value
get
public abstract V get(T obj)
Gets the current value held in the field of the given object managed
by this updater.
obj
- An object whose field to get
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.
obj
- An object whose field to get and setnewValue
- 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.
obj
- An object whose field to setnewValue
- the new value
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.
obj
- An object whose field to setnewValue
- the new value
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.
obj
- An object whose field to conditionally setexpect
- the expected valueupdate
- the new value