如何在 Java 多线程中从线程 2 设置线程 1 的布尔标志 [英] how to set boolean flag of thread-1 from thread-2 in Java multithreading

问题描述

我正在编写一个简单的 multithreaded 应用程序，它涉及三个线程:Thread-1、Thread-2 和 main.

I am writing a simple multithreaded application that involves three threads: Thread-1, Thread-2 and main.

Thread-1 是一个 random number 生成器类，它产生 random doubles 并提供给 线程 2.

Thread-1 is a random number generator class that produces random doubles and feeds to Thread-2.

Thread-2 消耗 的数字来计算平均值.我使用了 PipedOutputStream 那 Thread-1随机数.Thread-2 使用 PipedInputStream 吃掉 随机数.

Thread-2 consumes the numbers to calculate the average .I have used PipedOutputStream that Thread-1 feeds with random numbers. Thread-2 uses PipedInputStream to eat up the random numbers.

问题是::

如果 Thread-2 中的平均值超过 1E5，我想向 Thread-1 发出信号以停止生成数字.我在 Thread-1 中有一个 boolean flag 需要打开.我怎样才能做到这一点?

if the average exceeds 1E5 in Thread-2, I want to signal Thread-1 to stop producing numbers. I have a boolean flag in Thread-1 that needs to be turned on. How can I achieve this?

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.util.Random;

//

class NumGen extends Thread {

    PipedOutputStream pos;
    DataOutputStream dos;
    boolean isDone=false;

    public NumGen(PipedOutputStream pos){
        this.pos=pos;
        dos=new DataOutputStream(pos);
    }

    public void run(){
        while (!isDone){
            Random rand = new Random();
            try {
                dos.writeDouble(rand.nextDouble()+100.0);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

class RunningAvg extends Thread {

    PipedInputStream pis;
    DataInputStream dis;
    Double avg;
    int count;
    Double runningTotal;

    public RunningAvg(PipedInputStream pis){
        this.pis=pis;
        dis=new DataInputStream(pis);
            runningTotal=0.0;
    avg=0.0;
    }

    public void run(){
        try {
        while (dis.available()>0){
            count+=1;
            runningTotal+=dis.readDouble();
                avg=runningTotal/count;
                System.out.printf("The average in count no : %s is %s%n",count,avg);
                //if avg>1E5
                 //set NumGen.isDone=true
        }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }


public class InterThreadComm {

    public static void main(String[] args){


    try {
        PipedOutputStream pos= new PipedOutputStream();
        PipedInputStream pis = new PipedInputStream(pos);
        NumGen ng = new NumGen(pos);
        RunningAvg ra = new RunningAvg(pis);
        ng.start();
        ra.start();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    }


}

PS:代码永远运行，没有在控制台上打印任何东西，我还没有弄清楚为什么！！

PS: The code as it is runs forever without printing anything on console which I am yet to figure out why!!

推荐答案

您可以使用 AtomicBoolean 并将其传递给两个线程，原子类型是可访问的，多线程也是线程安全的.

You could use AtomicBoolean and pass it to the both threads, Atomic types is accessable throw multithreading also thread safe.

首先声明你将 isDone 标记为 AtomicBoolean

first declare you flag isDone as AtomicBoolean

private AtomicBoolean isDone;

然后声明一个 AtomicBoolean 对象并将其传递给两个线程

then declare one AtomicBoolean object and pass it to the both threads

PipedOutputStream pos= new PipedOutputStream();
PipedInputStream pis = new PipedInputStream(pos);
AtomicBoolean isDone = new AtomicBoolean();
NumGen ng = new NumGen(pos, isDone);
RunningAvg ra = new RunningAvg(pis, isDone);
ng.start();
ra.start();

最后，一旦你想停止生成数字，要求 Thread-2 将 isDone 设置为 false.

finally once you want to stop generting numbers ask Thread-2 to set the isDone false.

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