# 下面的代码运行 多线程的计算结果出不来，而且等了很久之后还会卡死，图片就是运行结果，只能出来一个，实在 没看出来问题在哪

package forkJoinPool;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;

/**
 * @author liuchaojun
 * @date 2018-9-10 下午03:50:24
 */
public class PrintTask2 extends RecursiveTask<Integer> {
    private static final long serialVersionUID = 1L;
    private static final int INDEX = 50;// 每个小任务执行50个
    private int start;
    private int end;
    private int arr[];

    /**
     * @param start
     * @param end
     * @param arr
     */
    public PrintTask2(int start, int end, int[] arr) {

        this.start = start;
        this.end = end;
        this.arr = arr;
    }

    /*
     * (non-Javadoc)
     * @see java.util.concurrent.RecursiveTask#compute()
     */
    @Override
    protected Integer compute() {
        int sum = 0;
        if (end - start < INDEX) {
            for (int i = start; i < end; i++) {
                sum += arr[i];
            }
            return sum;
        } else {
            int middle = (end - start) / 2;
            PrintTask2 taskLeft2 = new PrintTask2(start, middle, arr);
            PrintTask2 taskRight2 = new PrintTask2(middle, end, arr);
            //invokeAll(taskLeft2, taskRight2);
            taskLeft2.fork();
            taskRight2.fork();
            int leftValue = taskLeft2.join();// 当计算完成时返回计算结果。
            int rightValue = taskRight2.join();
            return leftValue + rightValue;
        }
    }

    public static void main(String[] args) throws InterruptedException, ExecutionException {
            int[] arr = new int[200];
            Random r = new Random();
            int tempSum = 0;//普通总数
            for (int i = 0; i < arr.length; i++) {
                tempSum += (arr[i]=r.nextInt(10));
            }
            System.out.println("普通总数结果为:"+tempSum);

            PrintTask2 task = new PrintTask2(0, arr.length, arr);
            ForkJoinPool pool = new ForkJoinPool();
            Future<Integer>  sum = pool.submit(task);
            System.out.println("多线程的执行结果："+sum.get());//get  如果需要，等待计算完成，然后检索其结果。
            pool.shutdown(); //关闭线程池
    }

}

这是运行结果！多线程运行结果没出来！

看下多线程是不是没有同步造成了死锁？