RecursiveTask 例子

1.先定义一个单线程工具类用来做对比

package ForkJoinTest;

import java.util.Random;

public class MakeArray {

   public static final int ARRAY_LENGTH= 400000000;
   public static final int THRESHOLD= 47;

   public static int[] makeArray(){
       Random r = new Random();
       int[] result =new int[ARRAY_LENGTH];
       for( int i = 0 ; i<ARRAY_LENGTH;i++){
           result[i]=r.nextInt(ARRAY_LENGTH*3);
       }
       return result;
   }

   public static void main(String[] args) {
       int count = 0 ;
       int[] src =    MakeArray.makeArray();
       long start = System.currentTimeMillis();
       for(int i = 0 ; i < src.length;i++   ){
           count = count+src[i];
       }
       System.out.println("the count is "+count+" spend time:"+(System.currentTimeMillis()-start)+"ms");
   }
}

2.写一个类，继承RecursiveTask

package ForkJoinTest;

import java.util.concurrent.RecursiveTask;

public class SumTask extends RecursiveTask<Integer> {

   // 当任务拆分到多小的时候不再进行拆分
   private final static int THRESHOLD = MakeArray.ARRAY_LENGTH/10;
   private int[] src;
   private int fromIndex;
   private int toIndex;

   public SumTask(int[] src, int fromIndex,int toIndex) {
       this.src=src;
       this.fromIndex=fromIndex;
       this.toIndex=toIndex;
   }

   @Override
   protected Integer compute() {
       //判断任务的大小是否是合适的范围
       if(toIndex-fromIndex<THRESHOLD){
           System.out.println(" from index = "+fromIndex+"toIndex="+toIndex);
           int count = 0;
           for(int i = fromIndex;i<=toIndex;i++){
               count=count+src[i];
           }
           return count;
       }else{
           int mid = (fromIndex+toIndex)/2;
           SumTask left = new SumTask(src, fromIndex, mid);
           SumTask right = new SumTask(src, mid+1, toIndex);
           invokeAll(left,right);
           return left.join()+right.join();
       }
   }
}

3.进行合并线程测试

   public static void main(String[] args) {
       int[] src = MakeArray.makeArray();
       ForkJoinPool pool = new ForkJoinPool();
       SumTask innerFind = new SumTask(src,0,src.length-1);
       long start = System.currentTimeMillis();
       pool.invoke(innerFind);
       System.out.println("The count is "+innerFind.join()+" spend time:"+
       (System.currentTimeMillis()-start)+"ms");
   }

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