2、线程的并发工具类-Fork/Join-使用的标准范式

 

Fork-Join使用的标准范式 ——> Fork/Join的同步用法同时演示返回结果值：统计整形数组中所有元素的和

SumArray

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{

        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);//模拟业务处理
			    	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);//new myTask

        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");

    }
}

SumNormal

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

MakeArray

package com.xiangxue.ch2.forkjoin.sum;

import java.util.Random;

/**
 *
 *产生整形数组
 */
public class MakeArray {
    //数组长度
    //public static final int ARRAY_LENGTH  = 100000000; //1千万
    public static final int ARRAY_LENGTH  = 10000; //1万

    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

SleepTools

package com.xiangxue.ch2.forkjoin.sum;

import java.util.Random;

/**
 *
 *产生整形数组
 */
public class MakeArray {
    //数组长度
    //public static final int ARRAY_LENGTH  = 100000000; //1千万
    public static final int ARRAY_LENGTH  = 10000; //1万

    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

 

Fork/Join的异步用法同时演示不要求返回值：遍历指定目录（含子目录）寻找指定类型文件 

package com.xiangxue.ch2.forkjoin;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;

/**
 *
 *类说明：遍历指定目录（含子目录）找寻指定类型文件
 */
public class FindDirsFiles extends RecursiveAction{

    private File path;//当前任务需要搜寻的目录

    public FindDirsFiles(File path) {
        this.path = path;
    }

    public static void main(String [] args){
        try {
            // 用一个 ForkJoinPool 实例调度总任务
            ForkJoinPool pool = new ForkJoinPool();
            FindDirsFiles task = new FindDirsFiles(new File("F:/"));

            pool.execute(task);//异步调用

            System.out.println("Task is Running......");
            Thread.sleep(1);
            int otherWork = 0;
            for(int i=0;i<100;i++){
                otherWork = otherWork+i;
            }
            System.out.println("Main Thread done sth......,otherWork="+otherWork);
            task.join();//阻塞的方法
            System.out.println("Task end");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

	@Override
	protected void compute() {
		
		List subTasks = new ArrayList<>();
		
		File[] files = path.listFiles();
		if(files!=null) {
			for(File file:files) {
				if(file.isDirectory()) {
					subTasks.add(new FindDirsFiles(file));
				}else {
					//遇到文件，检查
					if(file.getAbsolutePath().endsWith("txt")) {
						System.out.println("文件："+file.getAbsolutePath());
					}
				}
			}
			if(!subTasks.isEmpty()) {
				for(FindDirsFiles subTask:invokeAll(subTasks)) {
					subTask.join();//等待子任务执行完成
				}
			}
		}

	
	}
	
}