442 lines
15 KiB
Java
442 lines
15 KiB
Java
/*
|
|
* 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
|
|
* questions.
|
|
*/
|
|
|
|
/*
|
|
* 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 ExceptionInInitializerError(e);
|
|
}
|
|
}
|
|
|
|
@SuppressWarnings("serial") // Conditionally serializable
|
|
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 (with memory effects as specified by {@link
|
|
* VarHandle#compareAndSet}) 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 (with memory effects as specified by {@link
|
|
* VarHandle#compareAndSet}) 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 (with memory effects as specified by {@link
|
|
* VarHandle#compareAndSet}) 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 (with memory effects as specified by {@link
|
|
* VarHandle#compareAndSet}) 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);
|
|
}
|
|
|
|
}
|