src/java.base/share/classes/java/util/concurrent/atomic/AtomicReferenceArray.java

/*
 * 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.
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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 jdk.internal.misc.Unsafe;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.lang.reflect.Array;
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);
    /** @serial */
    @SuppressWarnings("serial") // Conditionally serializable
    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)));
        }
    }

    /**
     * {@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);

        final Unsafe U = Unsafe.getUnsafe();
        U.putReference(
            this,
            U.objectFieldOffset(AtomicReferenceArray.class, "array"),
            a
        );
    }

    // 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
     */
    @SuppressWarnings("unchecked")
    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
     */
    @SuppressWarnings("unchecked")
    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
     */
    @SuppressWarnings("unchecked")
    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 <em>witness value</em>, which will be the same as the
     * expected value if successful
     * @since 9
     */
    @SuppressWarnings("unchecked")
    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 <em>witness value</em>, which will be the same as the
     * expected value if successful
     * @since 9
     */
    @SuppressWarnings("unchecked")
    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 <em>witness value</em>, which will be the same as the
     * expected value if successful
     * @since 9
     */
    @SuppressWarnings("unchecked")
    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);
    }

    /**
     * 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#weakCompareAndSetAcquire}.
     *
     * @param i the index
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetAcquire(int i, E expectedValue, E newValue) {
        return AA.weakCompareAndSetAcquire(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#weakCompareAndSetRelease}.
     *
     * @param i the index
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetRelease(int i, E expectedValue, E newValue) {
        return AA.weakCompareAndSetRelease(array, i, expectedValue, newValue);
    }
}