java.util.concurrent.atomic.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 and volatile
semantics only with respect to other invocations of
compareAndSet and set.
Summary
Protected Constructors
Public Methods
abstract |
|
|
|
|
boolean |
compareAndSet(T obj, V expect, V update) |
abstract |
|
|
|
|
V |
get(T obj) |
|
|
|
|
|
V |
getAndSet(T obj, V newValue) |
|
|
|
static |
<U, W> |
AtomicReferenceFieldUpdater<U, W> |
newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) |
abstract |
|
|
|
|
void |
set(T obj, V newValue) |
abstract |
|
|
|
|
boolean |
weakCompareAndSet(T obj, V expect, V update) |
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait
Details
Protected Constructors
protected
AtomicReferenceFieldUpdater()
Protected do-nothing constructor for use by subclasses.
Public Methods
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.
Parameters
obj
| An object whose field to conditionally set |
expect
| the expected value |
update
| the new value |
public
abstract
V
get(T obj)
Get the current value held in the field by the given object.
Parameters
obj
| An object whose field to get |
public
V
getAndSet(T obj, V newValue)
Set to the given value and return the old value.
Parameters
obj
| An object whose field to get and set |
newValue
| the new value |
Creates 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. |
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.
Parameters
obj
| An object whose field to set |
newValue
| the new value
|
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.
Parameters
obj
| An object whose field to conditionally set |
expect
| the expected value |
update
| the new value |