compact1, compact2, compact3
java.util.concurrent.atomic
Class AtomicReferenceFieldUpdater<T,V>
- java.lang.Object
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- java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T,V>
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- Type Parameters:
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T- The type of the object holding the updatable field -
V- The type of the field
public abstract class AtomicReferenceFieldUpdater<T,V> extends Object
A reflection-based utility that enables atomic updates to designatedvolatilereference 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 asclass 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
compareAndSetmethod 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 ofcompareAndSetandseton the same updater.- Since:
- 1.5
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Constructor Summary
Constructors Modifier Constructor and Description protectedAtomicReferenceFieldUpdater()Protected do-nothing constructor for use by subclasses.
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method and Description VaccumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction)Atomically updates 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 Vget(T obj)Gets the current value held in the field of the given object managed by this updater.VgetAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction)Atomically updates 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.VgetAndSet(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.VgetAndUpdate(T obj, UnaryOperator<V> updateFunction)Atomically updates the field of the given object managed by this updater with the results of applying the given function, returning the previous value.abstract voidlazySet(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 voidset(T obj, V newValue)Sets the field of the given object managed by this updater to the given updated value.VupdateAndGet(T obj, UnaryOperator<V> updateFunction)Atomically updates 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.
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Constructor Detail
AtomicReferenceFieldUpdater
protected AtomicReferenceFieldUpdater()
Protected do-nothing constructor for use by subclasses.
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Method Detail
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:
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U- the type of instances of tclass -
W- the type of instances of vclass - Parameters:
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tclass- the class of the objects holding the field -
vclass- the class of the field -
fieldName- the name of the field to be updated - Returns:
- the updater
- Throws:
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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
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 tocompareAndSetandset, but not necessarily with respect to other changes in the field.- Parameters:
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obj- An object whose field to conditionally set -
expect- the expected value -
update- the new value - Returns:
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trueif successful
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 tocompareAndSetandset, 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.- Parameters:
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obj- An object whose field to conditionally set -
expect- the expected value -
update- the new value - Returns:
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trueif successful
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 ofcompareAndSet.- Parameters:
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obj- An object whose field to set -
newValue- 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.- Parameters:
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obj- An object whose field to set -
newValue- the new value - Since:
- 1.6
get
public abstract V get(T obj)
Gets the current value held in the field of the given object managed by this updater.- Parameters:
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obj- An object whose field to get - Returns:
- the current 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:
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obj- An object whose field to get and set -
newValue- the new value - Returns:
- the previous value
getAndUpdate
public final V getAndUpdate(T obj, UnaryOperator<V> updateFunction)
Atomically updates 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:
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obj- An object whose field to get and set -
updateFunction- a side-effect-free function - Returns:
- the previous value
- Since:
- 1.8
updateAndGet
public final V updateAndGet(T obj, UnaryOperator<V> updateFunction)
Atomically updates 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:
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obj- An object whose field to get and set -
updateFunction- a side-effect-free function - Returns:
- the updated value
- Since:
- 1.8
getAndAccumulate
public final V getAndAccumulate(T obj, V x, BinaryOperator<V> accumulatorFunction)
Atomically updates 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:
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obj- An object whose field to get and set -
x- the update value -
accumulatorFunction- a side-effect-free function of two arguments - Returns:
- the previous value
- Since:
- 1.8
accumulateAndGet
public final V accumulateAndGet(T obj, V x, BinaryOperator<V> accumulatorFunction)
Atomically updates 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:
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obj- An object whose field to get and set -
x- the update value -
accumulatorFunction- a side-effect-free function of two arguments - Returns:
- the updated value
- Since:
- 1.8
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