java.lang.Object
java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T,V>
- Type Parameters:
T- The type of the object holding the updatable fieldV- The type of the field
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(java.lang.Class<U>, java.lang.Class<W>, java.lang.String) will result in
a ClassCastException being thrown.
- Since:
- 1.5
-
Constructor Summary
ConstructorsModifierConstructorDescriptionprotectedProtected do-nothing constructor for use by subclasses. -
Method Summary
Modifier and TypeMethodDescriptionfinal VaccumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction) Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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.abstract booleancompareAndSet(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 VReturns the current value held in the field of the given object managed by this updater.final VgetAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction) Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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.Atomically sets the field of the given object managed by this updater to the given value and returns the old value.final VgetAndUpdate(T obj, UnaryOperator<V> updateFunction) Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.Object...)) the field of the given object managed by this updater with the results of applying the given function, returning the previous value.abstract voidEventually 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 voidSets the field of the given object managed by this updater to the given updated value.final VupdateAndGet(T obj, UnaryOperator<V> updateFunction) Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.Object...)) the field of the given object managed by this updater with the results of applying the given function, returning the updated value.abstract booleanweakCompareAndSet(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 Details
-
AtomicReferenceFieldUpdater
protected AtomicReferenceFieldUpdater()Protected do-nothing constructor for use by subclasses.
-
-
Method Details
-
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.- Type Parameters:
U- the type of instances of tclassW- the type of instances of vclass- Parameters:
tclass- the class of the objects holding the fieldvclass- the class of the fieldfieldName- the name of the field to be updated- Returns:
- the updater
- Throws:
ClassCastException- if the field is of the wrong typeIllegalArgumentException- if the field is not volatileRuntimeException- 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
-
compareAndSet
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 tocompareAndSetandset, but not necessarily with respect to other changes in the field.- Parameters:
obj- An object whose field to conditionally setexpect- the expected valueupdate- the new value- Returns:
trueif successful
-
weakCompareAndSet
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 tocompareAndSetandset, 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- An object whose field to conditionally setexpect- the expected valueupdate- the new value- Returns:
trueif successful
-
set
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 ofcompareAndSet.- Parameters:
obj- An object whose field to setnewValue- the new value
-
lazySet
Eventually sets the field of the given object managed by this updater to the given updated value.- Parameters:
obj- An object whose field to setnewValue- the new value- Since:
- 1.6
-
get
Returns 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
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 setnewValue- the new value- Returns:
- the previous value
-
getAndUpdate
Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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- An object whose field to get and setupdateFunction- a side-effect-free function- Returns:
- the previous value
- Since:
- 1.8
-
updateAndGet
Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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- An object whose field to get and setupdateFunction- a side-effect-free function- Returns:
- the updated value
- Since:
- 1.8
-
getAndAccumulate
Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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- An object whose field to get and setx- the update valueaccumulatorFunction- a side-effect-free function of two arguments- Returns:
- the previous value
- Since:
- 1.8
-
accumulateAndGet
Atomically updates (with memory effects as specified byVarHandle.compareAndSet(java.lang.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- An object whose field to get and setx- the update valueaccumulatorFunction- a side-effect-free function of two arguments- Returns:
- the updated value
- Since:
- 1.8
-