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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.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());
	}

	}

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