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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.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 VarHandle specification for descriptions of the properties of atomic accesses. 
Author:Doug Lea
Type parameters:
  • <E> – The base class of elements held in this array
Since:1.5
/**
 * 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.

Params:
  • length – the length of the array
/**
     * 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.

Params:
  • array – the array to copy elements from
Throws:
/**
     * 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.

Returns:the length of the array
/**
     * 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 i, with memory effects as specified by VarHandle.getVolatile. 
Params:
  • i – the index
Returns:the current value
/**
     * 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 i to newValue, with memory effects as specified by VarHandle.setVolatile. 
Params:
  • i – the index
  • newValue – the new value
/**
     * 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 i to newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • i – the index
  • newValue – the new value
Since:1.6
/**
     * 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 i to 
newValue and returns the old value, with memory effects as specified by VarHandle.getAndSet. 
Params:
  • i – the index
  • newValue – the new value
Returns:the previous value
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.compareAndSet. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful. False return indicates that the actual value was not equal to the expected value.
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
See Also:
Deprecated:This method has plain memory effects but the method name implies volatile memory effects (see methods such as compareAndExchange and compareAndSet). To avoid confusion over plain or volatile memory effects it is recommended that the method weakCompareAndSetPlain be used instead.
Returns:true if successful
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 VarHandle.compareAndSet) the element at index 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. 
Params:
  • i – the index
  • updateFunction – a side-effect-free function
Returns:the previous value
Since:1.8
/**
     * 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 VarHandle.compareAndSet) the element at index 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. 
Params:
  • i – the index
  • updateFunction – a side-effect-free function
Returns:the updated value
Since:1.8
/**
     * 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 VarHandle.compareAndSet) the element at index 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 i as its first argument, and the given update as the second argument. 
Params:
  • i – the index
  • x – the update value
  • accumulatorFunction – a side-effect-free function of two arguments
Returns:the previous value
Since:1.8
/**
     * 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 VarHandle.compareAndSet) the element at index 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 i as its first argument, and the given update as the second argument. 
Params:
  • i – the index
  • x – the update value
  • accumulatorFunction – a side-effect-free function of two arguments
Returns:the updated value
Since:1.8
/**
     * 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.

Returns:the String representation of the current values of array
/**
     * 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).

Params:
  • s – the stream
Throws:
/**
     * 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 i, with memory semantics of reading as if the variable was declared non-volatile. 
Params:
  • i – the index
Returns:the value
Since:9
/**
     * 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 i to newValue, with memory semantics of setting as if the variable was declared non-volatile and non-final. 
Params:
  • i – the index
  • newValue – the new value
Since:9
/**
     * 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 i, with memory effects as specified by VarHandle.getOpaque. 
Params:
  • i – the index
Returns:the value
Since:9
/**
     * 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 i to newValue, with memory effects as specified by VarHandle.setOpaque. 
Params:
  • i – the index
  • newValue – the new value
Since:9
/**
     * 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 i, with memory effects as specified by VarHandle.getAcquire. 
Params:
  • i – the index
Returns:the value
Since:9
/**
     * 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 i to newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • i – the index
  • newValue – the new value
Since:9
/**
     * 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 i to newValue if the element's current value, referred to as the witness
value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchange. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 i to newValue if the element's current value, referred to as the witness
value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeAcquire. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 i to newValue if the element's current value, referred to as the witness
value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeRelease. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSet. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetAcquire. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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 i to newValue if the element's current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetRelease. 
Params:
  • i – the index
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * 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);
    }

}