/*
 * 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.
 *
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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 sun.misc.Unsafe;

An object reference that may be updated atomically. See the atomic package specification for description of the properties of atomic variables. 
Author:
Doug Lea
Type parameters:
<V> – The type of object referred to by this reference
Since:
1.5/**
 * 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.
Params:
initialValue – the initial 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.
/**
     * Creates a new AtomicReference with null initial value.
     */
    public AtomicReference() {
    }

    
Gets the current value.
Returns:
the current value/**
     * Gets the current value.
     *
     * @return the current value
     */
    public final V get() {
        return value;
    }

    
Sets to the given value.
Params:
newValue – the new 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.
Params:
newValue – the new value
Since:
1.6/**
     * 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 == the expected value. 
Params:
expect – the expected value
update – the new value
Returns:
true if successful. False return indicates that
the actual value was not equal to the expected value./**
     * 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 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 == the expected value. 
May fail spuriously and does not provide ordering guarantees, so is only rarely an appropriate alternative to compareAndSet. 
Params:
expect – the expected value
update – the new value
Returns:
true if successful./**
     * Atomically sets the value to the given updated value
     * if the current value {@code ==} the expected value.
     *
     * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
     * and does not provide ordering guarantees, so is only rarely an
     * appropriate alternative to {@code compareAndSet}.
     *
     * @param expect the expected value
     * @param update the new value
     * @return 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.
Params:
newValue – the new value
Returns:
the previous value/**
     * Atomically sets to the given value and returns the old value.
     *
     * @param newValue the new value
     * @return the previous value
     */
    public final V getAndSet(V newValue) {
        while (true) {
            V x = get();
            if (compareAndSet(x, newValue))
                return x;
        }
    }

    
Returns the String representation of the current value.
Returns:
the String representation of the current value./**
     * Returns the String representation of the current value.
     * @return the String representation of the current value.
     */
    public String toString() {
        return String.valueOf(get());
    }

}