/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*
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* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent.atomic;
import java.util.function.
UnaryOperator;
import java.util.function.
BinaryOperator;
import sun.misc.
Unsafe;
/**
* An object reference that may be updated atomically. See the {@link
* java.util.concurrent.atomic} package specification for description
* of the properties of atomic variables.
* @since 1.5
* @author Doug Lea
* @param <V> The type of object referred to by this reference
*/
public class
AtomicReference<V> implements java.io.
Serializable {
private static final long
serialVersionUID = -1848883965231344442L;
private static final
Unsafe unsafe =
Unsafe.
getUnsafe();
private static final long
valueOffset;
static {
try {
valueOffset =
unsafe.
objectFieldOffset
(
AtomicReference.class.
getDeclaredField("value"));
} catch (
Exception ex) { throw new
Error(
ex); }
}
private volatile V
value;
/**
* Creates a new AtomicReference with the given initial value.
*
* @param initialValue the initial value
*/
public
AtomicReference(V
initialValue) {
value =
initialValue;
}
/**
* Creates a new AtomicReference with null initial value.
*/
public
AtomicReference() {
}
/**
* Gets the current value.
*
* @return the current value
*/
public final V
get() {
return
value;
}
/**
* Sets to the given value.
*
* @param newValue the new value
*/
public final void
set(V
newValue) {
value =
newValue;
}
/**
* Eventually sets to the given value.
*
* @param newValue the new value
* @since 1.6
*/
public final void
lazySet(V
newValue) {
unsafe.
putOrderedObject(this,
valueOffset,
newValue);
}
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final boolean
compareAndSet(V
expect, V
update) {
return
unsafe.
compareAndSwapObject(this,
valueOffset,
expect,
update);
}
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
*
* <p><a href="package-summary.html#weakCompareAndSet">May fail
* spuriously and does not provide ordering guarantees</a>, so is
* only rarely an appropriate alternative to {@code compareAndSet}.
*
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful
*/
public final boolean
weakCompareAndSet(V
expect, V
update) {
return
unsafe.
compareAndSwapObject(this,
valueOffset,
expect,
update);
}
/**
* Atomically sets to the given value and returns the old value.
*
* @param newValue the new value
* @return the previous value
*/
@
SuppressWarnings("unchecked")
public final V
getAndSet(V
newValue) {
return (V)
unsafe.
getAndSetObject(this,
valueOffset,
newValue);
}
/**
* Atomically updates the current value 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.
*
* @param updateFunction a side-effect-free function
* @return the previous value
* @since 1.8
*/
public final V
getAndUpdate(
UnaryOperator<V>
updateFunction) {
V
prev,
next;
do {
prev =
get();
next =
updateFunction.
apply(
prev);
} while (!
compareAndSet(
prev,
next));
return
prev;
}
/**
* Atomically updates the current value 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.
*
* @param updateFunction a side-effect-free function
* @return the updated value
* @since 1.8
*/
public final V
updateAndGet(
UnaryOperator<V>
updateFunction) {
V
prev,
next;
do {
prev =
get();
next =
updateFunction.
apply(
prev);
} while (!
compareAndSet(
prev,
next));
return
next;
}
/**
* Atomically updates the current value 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.
*
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the previous value
* @since 1.8
*/
public final V
getAndAccumulate(V
x,
BinaryOperator<V>
accumulatorFunction) {
V
prev,
next;
do {
prev =
get();
next =
accumulatorFunction.
apply(
prev,
x);
} while (!
compareAndSet(
prev,
next));
return
prev;
}
/**
* Atomically updates the current value 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.
*
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the updated value
* @since 1.8
*/
public final V
accumulateAndGet(V
x,
BinaryOperator<V>
accumulatorFunction) {
V
prev,
next;
do {
prev =
get();
next =
accumulatorFunction.
apply(
prev,
x);
} while (!
compareAndSet(
prev,
next));
return
next;
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value
*/
public
String toString() {
return
String.
valueOf(
get());
}
}