JUC-分支合并框架

一、原理

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

ForkJoinPool

分支合并池    类比=>   线程池

ForkJoinTask

ForkJoinTask    类比=>   FutureTask

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(); 
   } 
 } 

//代码

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();

    }
}