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	/*
	* 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);
	}

	}

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