ForkJoin分支合并框架

一、什么是ForkJoin

大数据里面有map reduce ，Java从JDK1.7开始借鉴了这种分而治之的思想，提供ForkJoin框架用于并行执行任务，它的思想就是讲一个大任务分割成若干小任务，最终汇总每个小任务的结果得到这个大任务的结果

Fork：把一个复杂任务进行分拆，大事化小
Join：把分拆任务的结果进行合并

二、3大类

2.1 ForkJoinPool
分支合并池 类比=> 线程池

2.2 ForkJoinTask
ForkJoinTask 类比=> FutureTask

2.3 RecursiveTask
递归任务：继承后可以实现递归(自己调自己)调用的任务

三、使用示例

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

class MyTask extends RecursiveTask<Integer>{
    private static final Integer ADJUST_VALUE = 10;
    private int begin;
    private int end;
    private int result;

    public MyTask(int begin, int end) {
        this.begin = begin;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        if((end - begin)<=ADJUST_VALUE){
            for(int i =begin;i <= end;i++){
                result = result + i;
            }
        }else{
            int middle = (begin + end)/2;
            MyTask task01 = new MyTask(begin,middle);
            MyTask task02 = new MyTask(middle+1,end);
            task01.fork();
            task02.fork();
            result =  task01.join() + task02.join();
        }


        return result;
    }
}


/**
 * 分支合并例子
 * ForkJoinPool
 * ForkJoinTask
 * RecursiveTask
 */
public class ForkJoinDemo {

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        MyTask myTask = new MyTask(0,100);
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Integer> forkJoinTask = forkJoinPool.submit(myTask);

        System.out.println(forkJoinTask.get());

        forkJoinPool.shutdown();
    }
}