/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
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*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* 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.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.function.BinaryOperator;
import java.util.function.UnaryOperator;
/**
* An object reference that may be updated atomically. See the {@link
* VarHandle} specification for descriptions of the properties of
* atomic accesses.
* @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 VarHandle VALUE;
static {
try {
MethodHandles.Lookup l = MethodHandles.lookup();
VALUE = l.findVarHandle(AtomicReference.class, "value", Object.class);
} catch (ReflectiveOperationException e) {
throw new Error(e);
}
}
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() {
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getVolatile}.
*
* @return the current value
*/
public final V get() {
return value;
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setVolatile}.
*
* @param newValue the new value
*/
public final void set(V newValue) {
value = newValue;
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(V newValue) {
VALUE.setRelease(this, newValue);
}
/**
* Atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#compareAndSet}.
*
* @param expectedValue the expected value
* @param newValue 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 expectedValue, V newValue) {
return VALUE.compareAndSet(this, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
*
* @deprecated This method has plain memory effects but the method
* name implies volatile memory effects (see methods such as
* {@link #compareAndExchange} and {@link #compareAndSet}). To avoid
* confusion over plain or volatile memory effects it is recommended that
* the method {@link #weakCompareAndSetPlain} be used instead.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @see #weakCompareAndSetPlain
*/
@Deprecated(since="9")
public final boolean weakCompareAndSet(V expectedValue, V newValue) {
return VALUE.weakCompareAndSetPlain(this, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetPlain(V expectedValue, V newValue) {
return VALUE.weakCompareAndSetPlain(this, expectedValue, newValue);
}
/**
* Atomically sets the value to {@code newValue} and returns the old value,
* with memory effects as specified by {@link VarHandle#getAndSet}.
*
* @param newValue the new value
* @return the previous value
*/
@SuppressWarnings("unchecked")
public final V getAndSet(V newValue) {
return (V)VALUE.getAndSet(this, 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 = get(), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.apply(prev);
if (weakCompareAndSetVolatile(prev, next))
return prev;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.apply(prev);
if (weakCompareAndSetVolatile(prev, next))
return next;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.apply(prev, x);
if (weakCompareAndSetVolatile(prev, next))
return prev;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = null;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.apply(prev, x);
if (weakCompareAndSetVolatile(prev, next))
return next;
haveNext = (prev == (prev = get()));
}
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value
*/
public String toString() {
return String.valueOf(get());
}
// jdk9
/**
* Returns the current value, with memory semantics of reading as
* if the variable was declared non-{@code volatile}.
*
* @return the value
* @since 9
*/
public final V getPlain() {
return (V)VALUE.get(this);
}
/**
* Sets the value to {@code newValue}, with memory semantics
* of setting as if the variable was declared non-{@code volatile}
* and non-{@code final}.
*
* @param newValue the new value
* @since 9
*/
public final void setPlain(V newValue) {
VALUE.set(this, newValue);
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getOpaque}.
*
* @return the value
* @since 9
*/
public final V getOpaque() {
return (V)VALUE.getOpaque(this);
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setOpaque}.
*
* @param newValue the new value
* @since 9
*/
public final void setOpaque(V newValue) {
VALUE.setOpaque(this, newValue);
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getAcquire}.
*
* @return the value
* @since 9
*/
public final V getAcquire() {
return (V)VALUE.getAcquire(this);
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param newValue the new value
* @since 9
*/
public final void setRelease(V newValue) {
VALUE.setRelease(this, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchange}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final V compareAndExchange(V expectedValue, V newValue) {
return (V)VALUE.compareAndExchange(this, expectedValue, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeAcquire}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final V compareAndExchangeAcquire(V expectedValue, V newValue) {
return (V)VALUE.compareAndExchangeAcquire(this, expectedValue, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeRelease}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final V compareAndExchangeRelease(V expectedValue, V newValue) {
return (V)VALUE.compareAndExchangeRelease(this, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSet}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetVolatile(V expectedValue, V newValue) {
return VALUE.weakCompareAndSet(this, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetAcquire}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetAcquire(V expectedValue, V newValue) {
return VALUE.weakCompareAndSetAcquire(this, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetRelease}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetRelease(V expectedValue, V newValue) {
return VALUE.weakCompareAndSetRelease(this, expectedValue, newValue);
}
}