Java线程池之ForkJoinPool

import java.io.IOException;
import java.util.Arrays;
import java.util.Random;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.RecursiveTask;

/**
 * 分割 合并 线程池
 * 类似于递归的归并排序，这个是多线程的递归排序
 * jdk1.7之后加的
 */
public class ForkJoinPool {

    static int[] nums = new int[1000000];
    static final int MAX_NUM = 50000;
    static Random random = new Random();

    static {
        for(int i=0; i<nums.length; i++) {
            nums[i] = random.nextInt(100);
        }
        System.out.println("总和1:" + Arrays.stream(nums).sum());
    }

    /**
     * ForkJoinPool里面必须是ForkJoinTask，
     * 直接继承ForkJoinTask类写起来比较麻烦，
     * 可以继承RecursiveAction(无返回值)和RecursiveTask(递归任务，有返回值)
     */
//    static class AddTask extends RecursiveAction {
//
//        int start, end;
//
//        public AddTask(int start, int end) {
//            this.start = start;
//            this.end = end;
//        }
//
//        @Override
//        protected void compute() {
//            if(end-start <= MAX_NUM) {
//                long sum = 0L;
//                for(int i=start; i<end; i++) sum += nums[i];
//                System.out.println("from:" + start + " to:" + end + " =" + sum);
//            }else{
//                int middle = start + (end - start) / 2;
//
//                AddTask subTask1 = new AddTask(start, middle);
//                AddTask subTask2 = new AddTask(middle, end);
//                subTask1.fork();
//                subTask2.fork();
//            }
//        }
//    }

    /**
     * 有返回值
     */
    static class AddTask extends RecursiveTask<Long> {

        int start, end;

        public AddTask(int start, int end) {
            this.start = start;
            this.end = end;
        }

        @Override
        protected Long compute() {
            if(end-start <= MAX_NUM) {
                long sum = 0L;
                for(int i=start; i<end; i++) sum += nums[i];
                System.out.println("from:" + start + " to:" + end + " =" + sum);
                return sum;
            }

            int middle = start + (end - start) / 2;
            AddTask subTask1 = new AddTask(start, middle);
            AddTask subTask2 = new AddTask(middle, end);
            subTask1.fork();
            subTask2.fork();
            return subTask1.join() + subTask2.join();
        }
    }

    public static void main(String[] args) {

        java.util.concurrent.ForkJoinPool pool = new java.util.concurrent.ForkJoinPool();
        AddTask task = new AddTask(0, nums.length);
        pool.execute(task);  //精灵线程
        System.out.println("总和2:" + task.join());
        try {
            System.in.read(); //阻塞主线程
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}