线程任务分支合并框架

1、原理

2、实用类

（1） ForkJoinPool

分支合并池 类比=> 线程池
（2） ForkJoinTask

ForkJoinTask 类比=> FutureTask
（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

 class Fibonacci extends RecursiveTask<Integer> {
   final int n;
   Fibonacci(int n) { this.n = n; }
   Integer compute() {
     if (n <= 1)
       return n;
     Fibonacci f1 = new Fibonacci(n - 1);
     f1.fork();
     Fibonacci f2 = new Fibonacci(n - 2);
     return f2.compute() + f1.join();
   }
 }

3、代码01

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 mid = (end+begin)/2;
            MyTask myTask1 = new MyTask(begin,mid);
            MyTask myTask2 = new MyTask(mid+1,end);
            myTask1.fork();
            myTask2.fork();
            result=myTask1.join()+myTask2.join();
        }
        return result;
    }
}



/**
 * 分支合并例子 0+++100
 * 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());

    }
}

4、代码02

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();
    }
}