/*

 * 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.lang.reflect.Array;

import java.lang.reflect.Field;

import java.util.Arrays;

import java.util.function.BinaryOperator;

import java.util.function.UnaryOperator;

/**

 * An array of object references in which elements may be updated

 * atomically.  See the {@link VarHandle} specification for

 * descriptions of the properties of atomic accesses.

 * @since 1.5

 * @author Doug Lea

 * @param <E> The base class of elements held in this array

 */

public class AtomicReferenceArray<E> implements java.io.Serializable {

    private static final long serialVersionUID = -6209656149925076980L;

    private static final VarHandle AA

        = MethodHandles.arrayElementVarHandle(Object[].class);

    private final Object[] array; // must have exact type Object[]

    /**

     * Creates a new AtomicReferenceArray of the given length, with all

     * elements initially null.

     *

     * @param length the length of the array

     */

    public AtomicReferenceArray(int length) {

        array = new Object[length];

    }

    /**

     * Creates a new AtomicReferenceArray with the same length as, and

     * all elements copied from, the given array.

     *

     * @param array the array to copy elements from

     * @throws NullPointerException if array is null

     */

    public AtomicReferenceArray(E[] array) {

        // Visibility guaranteed by final field guarantees

        this.array = Arrays.copyOf(array, array.length, Object[].class);

    }

    /**

     * Returns the length of the array.

     *

     * @return the length of the array

     */

    public final int length() {

        return array.length;

    }

    /**

     * Returns the current value of the element at index {@code i},

     * with memory effects as specified by {@link VarHandle#getVolatile}.

     *

     * @param i the index

     * @return the current value

     */

    @SuppressWarnings("unchecked")

    public final E get(int i) {

        return (E)AA.getVolatile(array, i);

    }

    /**

     * Sets the element at index {@code i} to {@code newValue},

     * with memory effects as specified by {@link VarHandle#setVolatile}.

     *

     * @param i the index

     * @param newValue the new value

     */

    public final void set(int i, E newValue) {

        AA.setVolatile(array, i, newValue);

    }

    /**

     * Sets the element at index {@code i} to {@code newValue},

     * with memory effects as specified by {@link VarHandle#setRelease}.

     *

     * @param i the index

     * @param newValue the new value

     * @since 1.6

     */

    public final void lazySet(int i, E newValue) {

        AA.setRelease(array, i, newValue);

    }

    /**

     * Atomically sets the element at index {@code i} to {@code

     * newValue} and returns the old value,

     * with memory effects as specified by {@link VarHandle#getAndSet}.

     *

     * @param i the index

     * @param newValue the new value

     * @return the previous value

     */

    @SuppressWarnings("unchecked")

    public final E getAndSet(int i, E newValue) {

        return (E)AA.getAndSet(array, i, newValue);

    }

    /**

     * Atomically sets the element at index {@code i} to {@code newValue}

     * if the element's current value {@code == expectedValue},

     * with memory effects as specified by {@link VarHandle#compareAndSet}.

     *

     * @param i the index

     * @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(int i, E expectedValue, E newValue) {

        return AA.compareAndSet(array, i, expectedValue, newValue);

    }

    /**

     * Possibly atomically sets the element at index {@code i} to

     * {@code newValue} if the element's 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 i the index

     * @param expectedValue the expected value

     * @param newValue the new value

     * @return {@code true} if successful

     * @see #weakCompareAndSetPlain

     */

    @Deprecated(since="9")

    public final boolean weakCompareAndSet(int i, E expectedValue, E newValue) {

        return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);

    }

    /**

     * Possibly atomically sets the element at index {@code i} to

     * {@code newValue} if the element's current value {@code == expectedValue},

     * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.

     *

     * @param i the index

     * @param expectedValue the expected value

     * @param newValue the new value

     * @return {@code true} if successful

     * @since 9

     */

    public final boolean weakCompareAndSetPlain(int i, E expectedValue, E newValue) {

        return AA.weakCompareAndSetPlain(array, i, expectedValue, newValue);

    }

    /**

     * Atomically updates (with memory effects as specified by {@link

     * VarHandle#compareAndSet}) the element at index {@code i} 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 i the index

     * @param updateFunction a side-effect-free function

     * @return the previous value

     * @since 1.8

     */

    public final E getAndUpdate(int i, UnaryOperator<E> updateFunction) {

        E prev = get(i), next = null;

        for (boolean haveNext = false;;) {

            if (!haveNext)

                next = updateFunction.apply(prev);

            if (weakCompareAndSetVolatile(i, prev, next))

                return prev;

            haveNext = (prev == (prev = get(i)));

        }

    }

    /**

     * Atomically updates (with memory effects as specified by {@link

     * VarHandle#compareAndSet}) the element at index {@code i} 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 i the index

     * @param updateFunction a side-effect-free function

     * @return the updated value

     * @since 1.8

     */

    public final E updateAndGet(int i, UnaryOperator<E> updateFunction) {

        E prev = get(i), next = null;

        for (boolean haveNext = false;;) {

            if (!haveNext)

                next = updateFunction.apply(prev);

            if (weakCompareAndSetVolatile(i, prev, next))

                return next;

            haveNext = (prev == (prev = get(i)));

        }

    }

    /**

     * Atomically updates (with memory effects as specified by {@link

     * VarHandle#compareAndSet}) the element at index {@code i} 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 of the element at index {@code i}

     * as its first argument, and the given update as the second

     * argument.

     *

     * @param i the index

     * @param x the update value

     * @param accumulatorFunction a side-effect-free function of two arguments

     * @return the previous value

     * @since 1.8

     */

    public final E getAndAccumulate(int i, E x,

                                    BinaryOperator<E> accumulatorFunction) {

        E prev = get(i), next = null;

        for (boolean haveNext = false;;) {

            if (!haveNext)

                next = accumulatorFunction.apply(prev, x);

            if (weakCompareAndSetVolatile(i, prev, next))

                return prev;

            haveNext = (prev == (prev = get(i)));

        }

    }

    /**

     * Atomically updates (with memory effects as specified by {@link

     * VarHandle#compareAndSet}) the element at index {@code i} 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 of the element at index {@code i}

     * as its first argument, and the given update as the second

     * argument.

     *

     * @param i the index

     * @param x the update value

     * @param accumulatorFunction a side-effect-free function of two arguments

     * @return the updated value

     * @since 1.8

     */

    public final E accumulateAndGet(int i, E x,

                                    BinaryOperator<E> accumulatorFunction) {

        E prev = get(i), next = null;

        for (boolean haveNext = false;;) {

            if (!haveNext)

                next = accumulatorFunction.apply(prev, x);

            if (weakCompareAndSetVolatile(i, prev, next))

                return next;

            haveNext = (prev == (prev = get(i)));

        }

    }

    /**

     * Returns the String representation of the current values of array.

     * @return the String representation of the current values of array

     */

    public String toString() {

        int iMax = array.length - 1;

        if (iMax == -1)

            return "[]";

        StringBuilder b = new StringBuilder();

        b.append('[');

        for (int i = 0; ; i++) {

            b.append(get(i));

            if (i == iMax)

                return b.append(']').toString();

            b.append(',').append(' ');

        }

    }

    /**

     * Reconstitutes the instance from a stream (that is, deserializes it).

     * @param s the stream

     * @throws ClassNotFoundException if the class of a serialized object

     *         could not be found

     * @throws java.io.IOException if an I/O error occurs

     */

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

        // Note: This must be changed if any additional fields are defined

        Object a = s.readFields().get("array", null);

        if (a == null || !a.getClass().isArray())

            throw new java.io.InvalidObjectException("Not array type");

        if (a.getClass() != Object[].class)

            a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);

        Field arrayField = java.security.AccessController.doPrivileged(

            (java.security.PrivilegedAction<Field>) () -> {

                try {

                    Field f = AtomicReferenceArray.class

                        .getDeclaredField("array");

                    f.setAccessible(true);

                    return f;

                } catch (ReflectiveOperationException e) {

                    throw new Error(e);

                }});

        try {

            arrayField.set(this, a);

        } catch (IllegalAccessException e) {

            throw new Error(e);

        }

    }

    // jdk9

    /**

     * Returns the current value of the element at index {@code i},

     * with memory semantics of reading as if the variable was declared

     * non-{@code volatile}.

     *

     * @param i the index

     * @return the value

     * @since 9

     */

    public final E getPlain(int i) {

        return (E)AA.get(array, i);

    }

    /**

     * Sets the element at index {@code i} to {@code newValue},

     * with memory semantics of setting as if the variable was

     * declared non-{@code volatile} and non-{@code final}.

     *

     * @param i the index

     * @param newValue the new value

     * @since 9

     */

    public final void setPlain(int i, E newValue) {

        AA.set(array, i, newValue);

    }

    /**

     * Returns the current value of the element at index {@code i},

     * with memory effects as specified by {@link VarHandle#getOpaque}.

     *

     * @param i the index

     * @return the value

     * @since 9

     */

    public final E getOpaque(int i) {

        return (E)AA.getOpaque(array, i);

    }

    /**

     * Sets the element at index {@code i} to {@code newValue},

     * with memory effects as specified by {@link VarHandle#setOpaque}.

     *

     * @param i the index

     * @param newValue the new value

     * @since 9

     */

    public final void setOpaque(int i, E newValue) {

        AA.setOpaque(array, i, newValue);

    }

    /**

     * Returns the current value of the element at index {@code i},

     * with memory effects as specified by {@link VarHandle#getAcquire}.

     *

     * @param i the index

     * @return the value

     * @since 9

     */

    public final E getAcquire(int i) {

        return (E)AA.getAcquire(array, i);

    }

    /**

     * Sets the element at index {@code i} to {@code newValue},

     * with memory effects as specified by {@link VarHandle#setRelease}.

     *

     * @param i the index

     * @param newValue the new value

     * @since 9

     */

    public final void setRelease(int i, E newValue) {

        AA.setRelease(array, i, newValue);

    }

    /**

     * Atomically sets the element at index {@code i} to {@code newValue}

     * if the element's current value, referred to as the <em>witness

     * value</em>, {@code == expectedValue},

     * with memory effects as specified by

     * {@link VarHandle#compareAndExchange}.

     *

     * @param i the index

     * @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 E compareAndExchange(int i, E expectedValue, E newValue) {

        return (E)AA.compareAndExchange(array, i, expectedValue, newValue);

    }

    /**

     * Atomically sets the element at index {@code i} to {@code newValue}

     * if the element's current value, referred to as the <em>witness

     * value</em>, {@code == expectedValue},

     * with memory effects as specified by

     * {@link VarHandle#compareAndExchangeAcquire}.

     *

     * @param i the index

     * @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 E compareAndExchangeAcquire(int i, E expectedValue, E newValue) {

        return (E)AA.compareAndExchangeAcquire(array, i, expectedValue, newValue);

    }

    /**

     * Atomically sets the element at index {@code i} to {@code newValue}

     * if the element's current value, referred to as the <em>witness

     * value</em>, {@code == expectedValue},

     * with memory effects as specified by

     * {@link VarHandle#compareAndExchangeRelease}.

     *

     * @param i the index

     * @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 E compareAndExchangeRelease(int i, E expectedValue, E newValue) {

        return (E)AA.compareAndExchangeRelease(array, i, expectedValue, newValue);

    }

    /**

     * Possibly atomically sets the element at index {@code i} to

     * {@code newValue} if the element's current value {@code == expectedValue},

     * with memory effects as specified by

     * {@link VarHandle#weakCompareAndSet}.

     *

     * @param i the index

     * @param expectedValue the expected value

     * @param newValue the new value

     * @return {@code true} if successful

     * @since 9

     */

    public final boolean weakCompareAndSetVolatile(int i, E expectedValue, E newValue) {

        return AA.weakCompareAndSet(array, i, expectedValue, newValue);

    }

    /**