AtomicReferenceFieldUpdater
public
abstract
class
AtomicReferenceFieldUpdater
extends Object
java.lang.Object | |
↳ | 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 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
}
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.
Summary
Protected constructors | |
---|---|
AtomicReferenceFieldUpdater()
Protected do-nothing constructor for use by subclasses. |
Public methods | |
---|---|
final
V
|
accumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction)
Atomically updates (with memory effects as specified by |
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 |
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 |
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 |
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 |
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 |
Inherited methods | |
---|---|
Protected constructors
AtomicReferenceFieldUpdater
protected AtomicReferenceFieldUpdater ()
Protected do-nothing constructor for use by subclasses.
Public methods
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 |
T : An object whose field to get and set |
x |
V : the update value |
accumulatorFunction |
BinaryOperator : a side-effect-free function of two arguments |
Returns | |
---|---|
V |
the updated value |
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 |
T : An object whose field to conditionally set |
expect |
V : the expected value |
update |
V : the new value |
Returns | |
---|---|
boolean |
true if successful |
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 |
T : An object whose field to get |
Returns | |
---|---|
V |
the current value |
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 |
T : An object whose field to get and set |
x |
V : the update value |
accumulatorFunction |
BinaryOperator : a side-effect-free function of two arguments |
Returns | |
---|---|
V |
the previous 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 |
T : An object whose field to get and set |
newValue |
V : the new value |
Returns | |
---|---|
V |
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 |
T : An object whose field to get and set |
updateFunction |
UnaryOperator : a side-effect-free function |
Returns | |
---|---|
V |
the previous 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 |
T : An object whose field to set |
newValue |
V : the new value |
newUpdater
public static 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 |
Class : the class of the objects holding the field |
vclass |
Class : the class of the field |
fieldName |
String : the name of the field to be updated |
Returns | |
---|---|
AtomicReferenceFieldUpdater<U, W> |
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 |
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 |
T : An object whose field to set |
newValue |
V : the new value |
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 |
T : An object whose field to get and set |
updateFunction |
UnaryOperator : a side-effect-free function |
Returns | |
---|---|
V |
the updated 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.
This operation may fail spuriously and does not provide
ordering guarantees, so is only rarely an appropriate
alternative to compareAndSet
.
Parameters | |
---|---|
obj |
T : An object whose field to conditionally set |
expect |
V : the expected value |
update |
V : the new value |
Returns | |
---|---|
boolean |
true if successful |