/*

 * 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 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}.

     *

     * @param expectedValue the expected value

     * @param newValue the new value

     * @return {@code true} if successful

     */

    public final boolean weakCompareAndSet(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);

    }

}