java - ExecutorService 池中的数组中所有元素的总和不起作用

Question

我试图理解 ExecutorService 并且我想对数组的所有元素求和。我做了两种方法，一种是连续求和(只是一个对所有元素求和的 for 循环)，另一种是与池同时求和。我的问题是，使用 ExecutorService 的总和几乎总是与序列总和不一致，有时甚至只有 1。

package sumArregloConc;

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

public class SumaArregloMain {

    private final static int cantElem = 1000;
    private static ExecutorService tpool = Executors.newCachedThreadPool();



    public static void main(String[] args)
    {

        int[] arreglo = generarArreglo(cantElem); //generate the array with random numbers

        System.out.println(sumaSerial(arreglo));
        System.out.println(sumaConcurrente(arreglo));
    }

    public static int sumaSerial(int[] arreglo)
    {
        int suma = 0;
        for(int i =0; i< arreglo.length; i++)
        {
            suma += arreglo[i];
        }

        return suma;

    }

    public static int sumaConcurrente(int[] arreglo)
    {
        AtomicInteger total = new AtomicInteger(0);

        for(int i = 1 ; i < cantElem; i++){

            int a = arreglo[i];
                Thread thread = new Thread(new Runnable(){
                    public void run() {
                        int res = a;
                        total.addAndGet(res);
                        return;
                }});
                tpool.submit(thread);
        }

        tpool.shutdown(); //wait for everything to finish
        return total.get();
    }

    public static int[] generarArreglo(int cantElem)
    {
        int[] arreglo = new int[cantElem];
        Random rand = new Random();

        for(int i = 0; i < cantElem; i++)
        {
            arreglo[i] = rand.nextInt(10);
        }

        return arreglo;
    }
}

谁能告诉我出了什么问题吗？

Answer 1

发现错误。首先，Eric 谈到了awaitTermination 和Runnable，但主要的错误是循环从i = 1 而不是i = 0 开始，愚蠢的错误。

    public static int sumaConcurrente(int[] arreglo)
    {
        AtomicInteger total = new AtomicInteger(0);

        for(int i = 0 ; i < cantElem; i++){

            int a = arreglo[i];

            tpool.submit(new Runnable(){
                public void run() {
                    total.addAndGet(a);
                    return;
                    }
                });
        }

        tpool.shutdown(); //wait for everything to finish
        try {
              tpool.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
            } catch (InterruptedException e) {  
            }
        return total.get();
    }