并发编程--线程的并发工具类

Posted 2021-03-13 zqlovesym

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1、线程的并发工具类

Fork-Join

什么是分而治之？

规模为N的问题，N<阈值，直接解决，N>阈值，将N分解为K个小规模子问题，子问题互相对立，与原问题形式相同，将子问题的解合并得到原问题的解

动态规范

工作密取

workStealing

Fork/Join使用的标准范式

技术图片

下面演示第一种用法：由于上下文切换的原因，所以性能上有可能不如单线程效果好。

package com.xiangxue.ch2.forkjoin.sum;

import java.util.Random;

/**
 * @author mark
 *产生整形数组
 */
public class MakeArray {
    //数组长度
    public static final int ARRAY_LENGTH  = 100000000;

    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;

    }
}

package com.xiangxue.ch2.forkjoin.sum;

import com.xiangxue.tools.SleepTools;

public class SumNormal {
    
    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++){
            //SleepTools.ms(1);
            count = count + src[i];
        }
        System.out.println("The count is "+count
                +" spend time:"+(System.currentTimeMillis()-start)+"ms");        
    }

}

package com.xiangxue.ch2.forkjoin.sum;

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

import com.xiangxue.tools.SleepTools;

public class SumArray {
    private static class SumTask extends RecursiveTask<Integer>{

        private final static int THRESHOLD = MakeArray.ARRAY_LENGTH/10;
        private int[] src; //表示我们要实际统计的数组
        private int fromIndex;//开始统计的下标
        private int toIndex;//统计到哪里结束的下标

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

        @Override
        protected Integer compute() {
            if(toIndex-fromIndex < THRESHOLD) {
                int count = 0;
                for(int i=fromIndex;i<=toIndex;i++) {
                    //SleepTools.ms(1);
                    count = count + src[i];
                }
                return count;
            }else {
                //fromIndex....mid....toIndex
                //1...................70....100
                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) {

        ForkJoinPool pool = new ForkJoinPool();
        int[] src = MakeArray.makeArray();

        SumTask innerFind = new SumTask(src,0,src.length-1);

        long start = System.currentTimeMillis();

        pool.invoke(innerFind);//同步调用
        System.out.println("Task is Running.....");

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

    }
}