java - 并发方法的 ArrayIndexOutOfBoundsException 方法包括

Question

我想对并发技术的不同方法进行一些比较。

但它会抛出下一个异常:

Warmup
BaseLine     :      21246915
============================
Cycles       :         50000
Exception in thread "pool-1-thread-3" Exception in thread "pool-1-thread-5" java.lang.ArrayIndexOutOfBoundsException: 100000
    at concurrency.BaseLine.accumulate(SynchronizationComparisons.java:89)
    at concurrency.Accumulator$Modifier.run(SynchronizationComparisons.java:39)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:744)
java.lang.ArrayIndexOutOfBoundsException: 100000
    at concurrency.BaseLine.accumulate(SynchronizationComparisons.java:89)
    at concurrency.Accumulator$Modifier.run(SynchronizationComparisons.java:39)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:744)

这里是代码:

import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import java.util.*;

import static net.mindview.util.Print.*;

abstract class Accumulator {
    public static long cycles = 50000L;
    // Number of Modifiers and Readers during each test:
    private static final int N = 4;
    public static ExecutorService exec = Executors.newFixedThreadPool(N * 2);
    private static CyclicBarrier barrier = new CyclicBarrier(N * 2 + 1);
    protected volatile int index = 0;
    protected volatile long value = 0;
    protected long duration = 0;
    protected String id = "error";
    protected final static int SIZE = 100000;
    protected static int[] preLoaded = new int[SIZE];
    static {
        // Load the array of random numbers:
        Random rand = new Random(47);
        for (int i = 0; i < SIZE; i++)
            preLoaded[i] = rand.nextInt();
    }

    public abstract void accumulate();

    public abstract long read();

    private class Modifier implements Runnable {
        public void run() {
            for (long i = 0; i < cycles; i++)
                accumulate();
            try {
                barrier.await();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }

    private class Reader implements Runnable {
        @SuppressWarnings("unused")
        private volatile long value;

        public void run() {
            for (long i = 0; i < cycles; i++)
                value = read();
            try {
                barrier.await();
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }

    public void timedTest() {
        long start = System.nanoTime();
        for (int i = 0; i < N; i++) {
            exec.execute(new Modifier());
            exec.execute(new Reader());
        }
        try {
            barrier.await();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        duration = System.nanoTime() - start;
        printf("%-13s: %13d\n", id, duration);
    }

    public static void report(Accumulator acc1, Accumulator acc2) {
        printf("%-22s: %.2f\n", acc1.id + "/" + acc2.id, (double) acc1.duration / (double) acc2.duration);
    }
}

class BaseLine extends Accumulator {
    {
        id = "BaseLine";
    }

    public void accumulate() {
        value += preLoaded[index++];
        if (index >= SIZE)
            index = 0;
    }

    public long read() {
        return value;
    }
}

class SynchronizedTest extends Accumulator {
    {
        id = "synchronized";
    }

    public synchronized void accumulate() {
        value += preLoaded[index++];
        if (index >= SIZE)
            index = 0;
    }

    public synchronized long read() {
        return value;
    }
}

class LockTest extends Accumulator {
    {
        id = "Lock";
    }
    private Lock lock = new ReentrantLock();

    public void accumulate() {
        lock.lock();
        try {
            value += preLoaded[index++];
            if (index >= SIZE)
                index = 0;
        } finally {
            lock.unlock();
        }
    }

    public long read() {
        lock.lock();
        try {
            return value;
        } finally {
            lock.unlock();
        }
    }
}

class AtomicTest extends Accumulator {
    {
        id = "Atomic";
    }
    private AtomicInteger index = new AtomicInteger(0);
    private AtomicLong value = new AtomicLong(0);

    public void accumulate() {
        // Oops! Relying on more than one Atomic at
        // a time doesn't work. But it still gives us
        // a performance indicator:
        int i = index.getAndIncrement();
        value.getAndAdd(preLoaded[i]);
        if (++i >= SIZE)
            index.set(0);
    }

    public long read() {
        return value.get();
    }
}

public class SynchronizationComparisons {
    static BaseLine baseLine = new BaseLine();
    static SynchronizedTest synch = new SynchronizedTest();
    static LockTest lock = new LockTest();
    static AtomicTest atomic = new AtomicTest();

    static void test() {
        print("============================");
        printf("%-12s : %13d\n", "Cycles", Accumulator.cycles);
        baseLine.timedTest();
        synch.timedTest();
        lock.timedTest();
        atomic.timedTest();
        Accumulator.report(synch, baseLine);
        Accumulator.report(lock, baseLine);
        Accumulator.report(atomic, baseLine);
        Accumulator.report(synch, lock);
        Accumulator.report(synch, atomic);
        Accumulator.report(lock, atomic);
    }

    public static void main(String[] args) {
        int iterations = 5; // Default
        if (args.length > 0) // Optionally change iterations
            iterations = new Integer(args[0]);
        // The first time fills the thread pool:
        print("Warmup");
        baseLine.timedTest();
        // Now the initial test doesn't include the cost
        // of starting the threads for the first time.
        // Produce multiple data points:
        for (int i = 0; i < iterations; i++) {
            test();
            Accumulator.cycles *= 2;
        }
        Accumulator.exec.shutdown();
    }
}

如何解决这个问题？

Answer 1

数组preLoaded的大小为100000。因此，有效索引从0开始到99999，因为数组索引从开始0 。您需要交换方法 accumulate()

中的语句

改变这个

        value += preLoaded[index++]; //index validity is not done
        if (index >= SIZE)
            index = 0;

到

        if (index >= SIZE)
            index = 0;
        value += preLoaded[index++]; // index validity is done and controlled

这不会使索引变为 100000。在访问索引值之前，当索引变为 100000 时，它会变为 0。

注意:上述代码仅在多线程环境中存在漏洞。上面的代码在单线程下可以正常工作。