java并发AtomicIntegerArray

Posted 2022-06-10 juncaif

java并发AtomicIntegerArray

AtomicIntegerArray的原子性

AtomicIntegerArray的原子性是对数组的元素的，不是数组。

源码基于openjdk 1.8

/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

/*
 *
 *
 *
 *
 *
 * 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.util.function.IntUnaryOperator;
import java.util.function.IntBinaryOperator;
import sun.misc.Unsafe;

/**
 * An @code int array in which elements 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
 */
public class AtomicIntegerArray implements java.io.Serializable 
    private static final long serialVersionUID = 2862133569453604235L;

    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final int base = unsafe.arrayBaseOffset(int[].class);
    private static final int shift;
    private final int[] array;

    static 
        int scale = unsafe.arrayIndexScale(int[].class);
        if ((scale & (scale - 1)) != 0)
            throw new Error("data type scale not a power of two");
        shift = 31 - Integer.numberOfLeadingZeros(scale);
    

    private long checkedByteOffset(int i) 
        if (i < 0 || i >= array.length)
            throw new IndexOutOfBoundsException("index " + i);

        return byteOffset(i);
    

    private static long byteOffset(int i) 
        return ((long) i << shift) + base;
    

    /**
     * Creates a new AtomicIntegerArray of the given length, with all
     * elements initially zero.
     *
     * @param length the length of the array
     */
    public AtomicIntegerArray(int length) 
        array = new int[length];
    

    /**
     * Creates a new AtomicIntegerArray 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 AtomicIntegerArray(int[] array) 
        // Visibility guaranteed by final field guarantees
        this.array = array.clone();
    

    /**
     * Returns the length of the array.
     *
     * @return the length of the array
     */
    public final int length() 
        return array.length;
    

    /**
     * Gets the current value at position @code i.
     *
     * @param i the index
     * @return the current value
     */
    public final int get(int i) 
        return getRaw(checkedByteOffset(i));
    

    private int getRaw(long offset) 
        return unsafe.getIntVolatile(array, offset);
    

    /**
     * Sets the element at position @code i to the given value.
     *
     * @param i the index
     * @param newValue the new value
     */
    public final void set(int i, int newValue) 
        unsafe.putIntVolatile(array, checkedByteOffset(i), newValue);
    

    /**
     * Eventually sets the element at position @code i to the given value.
     *
     * @param i the index
     * @param newValue the new value
     * @since 1.6
     */
    public final void lazySet(int i, int newValue) 
        unsafe.putOrderedInt(array, checkedByteOffset(i), newValue);
    

    /**
     * Atomically sets the element at position @code i to the given
     * value and returns the old value.
     *
     * @param i the index
     * @param newValue the new value
     * @return the previous value
     */
    public final int getAndSet(int i, int newValue) 
        return unsafe.getAndSetInt(array, checkedByteOffset(i), newValue);
    

    /**
     * Atomically sets the element at position @code i to the given
     * updated value if the current value @code == the expected value.
     *
     * @param i the index
     * @param expect the expected value
     * @param update 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, int expect, int update) 
        return compareAndSetRaw(checkedByteOffset(i), expect, update);
    

    private boolean compareAndSetRaw(long offset, int expect, int update) 
        return unsafe.compareAndSwapInt(array, offset, expect, update);
    

    /**
     * Atomically sets the element at position @code i to the given
     * updated value if the current value @code == the expected value.
     *
     * <p><a href="package-summary.html#weakCompareAndSet">May fail
     * spuriously and does not provide ordering guarantees</a>, so is
     * only rarely an appropriate alternative to @code compareAndSet.
     *
     * @param i the index
     * @param expect the expected value
     * @param update the new value
     * @return @code true if successful
     */
    public final boolean weakCompareAndSet(int i, int expect, int update) 
        return compareAndSet(i, expect, update);
    

    /**
     * Atomically increments by one the element at index @code i.
     *
     * @param i the index
     * @return the previous value
     */
    public final int getAndIncrement(int i) 
        return getAndAdd(i, 1);
    

    /**
     * Atomically decrements by one the element at index @code i.
     *
     * @param i the index
     * @return the previous value
     */
    public final int getAndDecrement(int i) 
        return getAndAdd(i, -1);
    

    /**
     * Atomically adds the given value to the element at index @code i.
     *
     * @param i the index
     * @param delta the value to add
     * @return the previous value
     */
    public final int getAndAdd(int i, int delta) 
        return unsafe.getAndAddInt(array, checkedByteOffset(i), delta);
    

    /**
     * Atomically increments by one the element at index @code i.
     *
     * @param i the index
     * @return the updated value
     */
    public final int incrementAndGet(int i) 
        return getAndAdd(i, 1) + 1;
    

    /**
     * Atomically decrements by one the element at index @code i.
     *
     * @param i the index
     * @return the updated value
     */
    public final int decrementAndGet(int i) 
        return getAndAdd(i, -1) - 1;
    

    /**
     * Atomically adds the given value to the element at index @code i.
     *
     * @param i the index
     * @param delta the value to add
     * @return the updated value
     */
    public final int addAndGet(int i, int delta) 
        return getAndAdd(i, delta) + delta;
    


    /**
     * Atomically updates 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 int getAndUpdate(int i, IntUnaryOperator updateFunction) 
        long offset = checkedByteOffset(i);
        int prev, next;
        do 
            prev = getRaw(offset);
            next = updateFunction.applyAsInt(prev);
         while (!compareAndSetRaw(offset, prev, next));
        return prev;
    

    /**
     * Atomically updates 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 int updateAndGet(int i, IntUnaryOperator updateFunction) 
        long offset = checkedByteOffset(i);
        int prev, next;
        do 
            prev = getRaw(offset);
            next = updateFunction.applyAsInt(prev);
         while (!compareAndSetRaw(offset, prev, next));
        return next;
    

    /**
     * Atomically updates 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 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 int getAndAccumulate(int i, int x,
                                      IntBinaryOperator accumulatorFunction) 
        long offset = checkedByteOffset(i);
        int prev, next;
        do 
            prev = getRaw(offset);
            next = accumulatorFunction.applyAsInt(prev, x);
         while (!compareAndSetRaw(offset, prev, next));
        return prev;
    

    /**
     * Atomically updates 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 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 int accumulateAndGet(int i, int x,
                                      IntBinaryOperator accumulatorFunction) 
        long offset = checkedByteOffset(i);
        int prev, next;
        do 
            prev = getRaw(offset);
            next = accumulatorFunction.applyAsInt(prev, x);
         while (!compareAndSetRaw(offset, prev, next));
        return next;
    

    /**
     * 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(getRaw(byteOffset(i)));
            if (i == iMax)
                return b.append(']').toString();
            b.append(',').append(' ');
        
    

AtomicIntegerArray方法测试

package javalearn.javabase.thread.atomic;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.atomic.AtomicIntegerArray;
@Slf4j
public class AtomicIntegerArrTest 
    public static void main(String[] args) 
        int [] arr1 = new int[]10,20,30,40;

        AtomicIntegerArray integerArray =new AtomicIntegerArray(arr1);
        for(int i= 0;i<arr1.length;i++)
        
            log.info("init arr [] is ",i,integerArray.get(i));
            log.info("decrementAndGet arr[] is ",i,integerArray.decrementAndGet(i));
            log.info("getAndIncrement arr[] is ",i,integerArray.getAndIncrement(i));
            log.info("compareAndSet arr[] is ",i,integerArray.compareAndSet(i,10,100));
            log.info("addAndGet 5 arr[] is ",i,integerArray.addAndGet(i,5));

        

    

测试结果

12:39:09.205 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - init arr [0] is 10
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - decrementAndGet arr[0] is 9
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - getAndIncrement arr[0] is 9
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - compareAndSet arr[0] is true
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - addAndGet 5 arr[0] is 105
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - init arr [1] is 20
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - decrementAndGet arr[1] is 19
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - getAndIncrement arr[1] is 19
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - compareAndSet arr[1] is false
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - addAndGet 5 arr[1] is 25
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - init arr [2] is 30
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - decrementAndGet arr[2] is 29
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - getAndIncrement arr[2] is 29
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - compareAndSet arr[2] is false
12:39:09.216 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - addAndGet 5 arr[2] is 35
12:39:09.217 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - init arr [3] is 40
12:39:09.217 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - decrementAndGet arr[3] is 39
12:39:09.217 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - getAndIncrement arr[3] is 39
12:39:09.217 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - compareAndSet arr[3] is false
12:39:09.217 [main] INFO javalearn.javabase.thread.atomic.AtomicIntegerArrTest - addAndGet 5 arr[3] is 45