数组

public class MakeArray {
    //数组长度
    public static final int ARRAY_LENGTH  = 40000000;
    public final static int THRESHOLD = 47;

    public static int[] makeArray() {

        //new一个随机数发生器
        Random r = new Random();
        int[] result = new int[ARRAY_LENGTH];
        for(int i=0;i<ARRAY_LENGTH;i++){
            //用随机数填充数组
            result[i] =  r.nextInt(ARRAY_LENGTH*3);
        }
        return result;

    }
}

 

 ForkJoin执行多线程累加

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

/**
 * ForkJoin执行累加
 */
public class SumArray {
    private static class SumTask extends RecursiveTask<Integer>{

        /*阈值*/
        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() {
            /*任务的大小是否合适*/
            if (toIndex - fromIndex < THRESHOLD){
//                System.out.println(" from index = "+fromIndex
//                        +" toIndex="+toIndex);
                int count = 0;
                for(int i= fromIndex;i<=toIndex;i++){
                	//SleepTools.ms(1);
                	count = count + src[i];
                }
                return count;
            }else{
                //fromIndex....mid.....toIndex
                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();
            }
        }
    }


    public static void main(String[] args) {

        int[] src = MakeArray.makeArray();
        /*new出池的实例*/
        ForkJoinPool pool = new ForkJoinPool();
        /*new出Task的实例*/
        SumTask innerFind = new SumTask(src,0,src.length-1);

        long start = System.currentTimeMillis();

        pool.invoke(innerFind);
        System.out.println("Task is Running.....");

        System.out.println("The count is "+innerFind.join()
                +" spend time:"+(System.currentTimeMillis()-start)+"ms");

    }
}