如何等待所有线程完成执行？ [英] How to wait until all threads complete their execution?

问题描述

假设我正在使用HTTP请求库来下载文件。这个库在里面使用线程。现在，我想在主线程上等待，直到其他线程完成它们的执行。

所有其他解决方案，我发现通过谷歌搜索只有工作，如果我有权访问线程库中使用的变量。但是这些都是我无法访问的。

以下是我目前使用的内容：

  package smartzero.eightnoteight.testfirebase; 
 
 import com.firebase.client.AuthData; 
 import com.firebase.client.Firebase; 
 import com.firebase.client.FirebaseError; 
 
 import java.util.Scanner; 
 
 public class Main {
 public static void main（String [] args）{
 Scanner in = new Scanner（System.in）; 
 System.out.print（email：）; 
 String email = in.nextLine（）; 
 System.out.print（password：）; 
 String password = in.nextLine（）; 
 Firebase fb =新的Firebase（https://nullform.firebaseio.com）; 
 fb.authWithPassword（email，password，new AuthResultHandler（））; 
尝试{
 Thread.sleep（1000000）; 
} catch（InterruptedException e）{
 e.printStackTrace（）; 
} 
} 
 
公共静态类AuthResultHandler实现Firebase.AuthResultHandler {
 @覆盖
公共onAuthenticated（的authData的authData）无效{
系统.out.println（认证成功）; 
 String uid = authData.getUid（）; 
新的RunTests（uid）; 
 
 $ b @Override 
 public void onAuthenticationError（FirebaseError firebaseError）{
 System.out.println（authentication failed。）; 
 
 
 $ b $ / code $ / pre 
 $ b $ PS： Firebase使用firebase-client-jvm在我的电脑上。
解决方案
您应该使用Firebase提供的事件：
 b 
 $ b'pre>  fb.authWithPassword（电子邮件，密码，新AuthResultHandler（）{
 @覆盖
公共无效onAuthenticated（的authData的authData）{ 
 //做一些事情，如果认证成功
 
 $ b @Override 
 public void onAuthenticationError（FirebaseError error）{
 //处理错误
 } 
}）; 
  

你可以，如果你真的想在主要等待的话：



  void main（String [] args）{
 boolean finished = false; 
 fb.authWithPassword（电子邮件，密码，新AuthResultHandler（）{
 @覆盖
公共无效onAuthenticated（的authData的authData）{
结束= TRUE; 
} 
}）; 
 while（！finished）{
 Thread.sleep（1）; 
} 
} 
  

更多的伪代码。它没有捕获中断的异常，并且如果有错误（onAuthenticationError）则永远阻塞。我也不会推荐这个。忙碌的等待几乎不是一个好主意。

Say I'm using a HTTP requests library for downloading files. This library uses threads inside. Now, I want to wait on the main thread until other threads complete their execution.

All the other solutions that I found by googling only work if I have access to the Thread variables that were used in the library. But these are not accessible to me.

Here's what i'm using currently:

package smartzero.eightnoteight.testfirebase;

import com.firebase.client.AuthData;
import com.firebase.client.Firebase;
import com.firebase.client.FirebaseError;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("email: ");
        String email = in.nextLine();
        System.out.print("password: ");
        String password = in.nextLine();
        Firebase fb = new Firebase("https://nullform.firebaseio.com");
        fb.authWithPassword(email, password, new AuthResultHandler());
        try {
            Thread.sleep(1000000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static class AuthResultHandler implements Firebase.AuthResultHandler {
        @Override
        public void onAuthenticated(AuthData authData) {
            System.out.println("authentication successful");
            String uid = authData.getUid();
            new RunTests(uid);
        }

        @Override
        public void onAuthenticationError(FirebaseError firebaseError) {
            System.out.println("authentication failed.");
        }
    }
}

PS: i'm testing firebase using firebase-client-jvm on my pc.

解决方案

You should use the events provided by Firebase:

fb.authWithPassword(email, password, new AuthResultHandler(){
    @Override
    public void onAuthenticated(AuthData authData) {
        //do something if authentication successful
    }

    @Override
    public void onAuthenticationError(FirebaseError error) {
        //handle error
    }
});

You could, if you really want to wait in the main do this:

void main(String[] args) {
    boolean finished = false;
    fb.authWithPassword(email, password, new AuthResultHandler(){
        @Override
        public void onAuthenticated(AuthData authData) {
            finished = true;
        }
    });
    while (!finished){
        Thread.sleep(1);
    }
}

Thats more of a pseudocode. It doesnt catch the interrupted exception and blocks forever if there is an error (onAuthenticationError). Also i would not recommend this. Busy waiting is almost never a good idea.

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