T
- The type of the object holding the updatable fieldV
- The type of the fieldpublic abstract class AtomicReferenceFieldUpdater<T,V> extends Object
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.
Modifier | Constructor | Description |
---|---|---|
protected |
Protected do-nothing constructor for use by subclasses. |
Modifier and Type | Method | Description |
---|---|---|
final V |
accumulateAndGet |
Atomically updates (with memory effects as specified by VarHandle.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 boolean |
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. |
abstract V |
get |
Returns the current value held in the field of the given object managed by this updater. |
final V |
getAndAccumulate |
Atomically updates (with memory effects as specified by VarHandle.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. |
V |
getAndSet |
Atomically sets the field of the given object managed by this updater to the given value and returns the old value. |
final V |
getAndUpdate |
Atomically updates (with memory effects as specified by VarHandle.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 void |
lazySet |
Eventually sets the field of the given object managed by this updater to the given updated value. |
static <U, |
newUpdater |
Creates and returns an updater for objects with the given field. |
abstract void |
set |
Sets the field of the given object managed by this updater to the given updated value. |
final V |
updateAndGet |
Atomically updates (with memory effects as specified by VarHandle.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 boolean |
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. |
protected AtomicReferenceFieldUpdater()
public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName)
U
- the type of instances of tclassW
- the type of instances of vclasstclass
- the class of the objects holding the fieldvclass
- the class of the fieldfieldName
- the name of the field to be updatedClassCastException
- 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 controlpublic abstract boolean compareAndSet(T obj, V expect, V update)
==
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 valuetrue
if successfulpublic abstract boolean weakCompareAndSet(T obj, V expect, V update)
==
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
.
obj
- An object whose field to conditionally setexpect
- the expected valueupdate
- the new valuetrue
if successfulpublic abstract void set(T obj, V newValue)
compareAndSet
.obj
- An object whose field to setnewValue
- the new valuepublic abstract void lazySet(T obj, V newValue)
obj
- An object whose field to setnewValue
- the new valuepublic abstract V get(T obj)
obj
- An object whose field to getpublic V getAndSet(T obj, V newValue)
obj
- An object whose field to get and setnewValue
- the new valuepublic final V getAndUpdate(T obj, UnaryOperator<V> updateFunction)
VarHandle.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.obj
- An object whose field to get and setupdateFunction
- a side-effect-free functionpublic final V updateAndGet(T obj, UnaryOperator<V> updateFunction)
VarHandle.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.obj
- An object whose field to get and setupdateFunction
- a side-effect-free functionpublic final V getAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction)
VarHandle.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.obj
- An object whose field to get and setx
- the update valueaccumulatorFunction
- a side-effect-free function of two argumentspublic final V accumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction)
VarHandle.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.obj
- An object whose field to get and setx
- the update valueaccumulatorFunction
- a side-effect-free function of two arguments
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/atomic/AtomicReferenceFieldUpdater.html