Question

我在java中使用Fork join pool进行多任务处理。现在我遇到了这样一种情况：对于每个任务，我需要点击一个url然后等待10分钟，然后再次点击另一个url来读取数据。现在问题是，对于那些10分钟，我的CPU处于空闲状态而没有启动另一个任务（超过fork join pool中定义的那些任务）。

static ForkJoinPool pool = new ForkJoinPool(10);
public static void main(String[] args){
    List<String> list = new ArrayList<>();
    for(int i=1; i<=100; i++){
        list.add("Str"+i);
    }
    final Tasker task = new Tasker(list);
    pool.invoke(task);

public class Tasker extends RecursiveAction{

    private static final long serialVersionUID = 1L;
    List<String> myList;
    public Tasker(List<String> checkersList) {
        super();
        this.myList = checkersList;
    }
    @Override
    protected void compute() {
        if(myList.size()==1){
            System.out.println(myList.get(0) + "start");
            //Date start = new Date();
            try {

                    Thread.sleep(10*60*1000);

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println(myList.get(0) + "Finished");
        }
        else{
            List<String> temp = new ArrayList<>();
            temp.add(  myList.get( myList.size()-1 )  );
            myList.remove( myList.size()-1 );

            Tasker left = new Tasker(myList);
            Tasker right = new Tasker(temp);

            left.fork();
            right.compute();
            left.join();
        }
    }

现在我该怎么办才能让CPU选择所有任务，然后等待它们。

Answer 1

不幸的是，ForkJoinPool在Thread.sleep()面前效果不佳，因为它设计用于很快完成的许多短任务，而不是长时间阻止的任务。

相反，对于您要完成的任务，我建议您使用ScheduledThreadPoolExecutor并将您的任务分为两部分。

import java.util.*;
import java.util.concurrent.*;

public class Main {
    static ScheduledThreadPoolExecutor pool = new ScheduledThreadPoolExecutor(10);
    public static void main(String[] args){
        for(int i=1; i<=100; i++){
            pool.schedule(new FirstHalf("Str"+i), 0, TimeUnit.NANOSECONDS);
        }
    }
    static class FirstHalf implements Runnable {
        String name;
        public FirstHalf(String name) {
            this.name = name;
        }
        public void run() {
            System.out.println(name + "start");
            pool.schedule(new SecondHalf(name), 10, TimeUnit.MINUTES);
        }
    }
    static class SecondHalf implements Runnable {
        String name;
        public SecondHalf(String name) {
            this.name = name;
        }
        public void run() {
            System.out.println(name + "Finished");
        }
    }
}

如果Java提供了一个允许在Thread.sleep()期间释放底层资源（即参与线程池的内核线程）的线程池，那么你应该使用它，但我现在不知道一个

Answer 2

根据docs forkJoin基本用法部分告诉：

if（我的工作部分足够小）直接做这项工作其他把我的工作分成两部分调用这两个部分并等待结果

希望如果您使用forkjoin

，这符合您的需求

public class Tasker extends RecursiveAction {
    static ForkJoinPool pool = new ForkJoinPool(10);
    static int threshold = 10;
    public static void main(String[] args){
        List<String> list = new ArrayList<>();
        for(int i=1; i<=100; i++){
           list.add("Str"+i);
        }
    final Tasker task = new Tasker(list);
    pool.invoke(task);
}


private static final long serialVersionUID = 1L;
List<String> myList;

public Tasker(List<String> checkersList) {
    super();
    this.myList = checkersList;
}

void computeDirectly() {
    for(String url : myList){
        System.out.println(url + " start");
    }
    //Date start = new Date();
    try {
        //keep hitting url
        while (true) {
            for(String url : myList) {
                //url hitting code here
                System.out.println(url + " hitting");
            }
            Thread.sleep(10 * 60 * 1000);
        }

    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    for(String url : myList){
        System.out.println(url + " Finished");
    }
}

@Override
protected void compute() {
    if (myList.size() <= threshold) {
        computeDirectly();
        return;
    }

    //temp list have only one url
    //List<String> temp = new ArrayList<>();
    //temp.add(  myList.get( myList.size()-1 )  );
    //myList.remove( myList.size()-1 );


    //Tasker left = new Tasker(myList);
    //Tasker right = new Tasker(temp);


    //left.fork();
    //right.compute();
    //left.join();

    List<String> first = new ArrayList<>();
    List<String> second = new ArrayList<>();

    //divide list
    int len = myList.size();
    int smHalf = len / 2;//smaller half

    first = myList.subList(0, smHalf);
    second = myList.subList(smHalf + 1, len);

    invokeAll(new Tasker(first), new Tasker(second));

}

}

等待ForkJoin Pool（Java）

2 个答案: