Question

给我正确的输出，但有时得到IndexOutOFBound Exception .....无法获得编译器完成的重新排序？

package com.array.thread;

import java.util.concurrent.*;

public class EvenOddProcessor {
    public static void main(String[] args) {

        CyclicBarrier barrier = new CyclicBarrier(6, new Runnable() {

            @Override
            public void run() {
                System.out.println("BARRIER BROKEN!!!");

            }
        });

        int[] array = new int[10];
        for (int i = 0; i < array.length; i++)
            array[i] = i;

        ArrayIndexProcessor evenIndexProcessor = new ArrayIndexProcessor(array,
                0, barrier);
        ArrayIndexProcessor oddIndexProcessor = new ArrayIndexProcessor(array,
                1, barrier);

        Thread t1 = new Thread(evenIndexProcessor, "Even_1");
        Thread t2 = new Thread(evenIndexProcessor, "Even_2");
        Thread t3 = new Thread(evenIndexProcessor, "Even_3");
        t1.start();
        t2.start();
        t3.start();

        Thread t4 = new Thread(oddIndexProcessor, "Odd_1");
        Thread t5 = new Thread(oddIndexProcessor, "Odd_2");
        Thread t6 = new Thread(oddIndexProcessor, "Odd_3");
        t4.start();
        t5.start();
        t6.start();

        System.out.println(">>>>>  Main thread is done");

    }
}

class ArrayIndexProcessor implements Runnable {

    private final CyclicBarrier barrier;

    private final int[] array;

    private volatile int currentPtr = 0;

    private Lock lock = new ReentrantLock();

    public ArrayIndexProcessor(int[] array, int startIndex,
            CyclicBarrier barrier) {
        this.array = array;
        this.currentPtr = startIndex;
        this.barrier = barrier;
    }

    public void run() {
        try {
            barrier.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            e.printStackTrace();
        }
        while (!(array.length == 0) && (currentPtr < array.length)) {
            lock.lock();
            try {
                System.out.println(Thread.currentThread().getName() + "="
                        + array[currentPtr]);
                currentPtr = currentPtr + 2;
            } finally {
                lock.unlock();
            }
        }
    }
}

Answer 1

    while (!(array.length == 0) && (currentPtr < array.length)) {
        lock.lock();

首先对currentPtr进行边界检查，然后锁定，然后使用currentPtr作为数组索引。由于您在三个线程中重用相同的Runnable实例，因此在此期间可能已修改currentPtr，从而导致越界索引。

为什么要获取ArrayIndexOutOfBoundsException？

1 个答案: