在多线程应用程序中通过标准I / O进行输入 [英] Taking input over standard I/O in multithreaded application

问题描述

我对多线程应用程序中的输入/输出或基本上与用户的交互有疑问。

I have a question about input/output, or basically interaction with the user, in multithreaded applications.

假设我有一个程序可以启动三个线程并等待让它们结束，然后再次启动它们

Let's say I have a program that starts three threads and waits for them to end, then starts them again

int main()
{
   while(true)
   {
      start_thread(1);
      start_thread(2);
      start_thread(3);
      //....
      join_thread(1);
      join_thread(2);
      join_thread(3);
   }
}

每个线程还输出 cout 。

我正在寻找一种方法来接收用户输入的内容（ cin ）而又不停止/阻碍主输入循环进行中。我如何实现解决方案？

I'm looking for a way to take input by the user (cin) without stopping / hindering the main loop in it's progress. How can I realize a solution?

我试图创建第四个线程，该线程一直在后台运行，并等待 cin 。对于测试用例，我将其修改为：

I've tried to create a fourth thread which is running in the background all the time and is waiting for input in cin. For the test case I modified it like this:

void* input_func(void* v)
{
    while(true)
    {
        string input;
        cin >> input;
        cout << "Input: " << input << endl;
    }
}

但是输入没有达到此功能。我认为问题在于，当 input_func 等待输入时，其他线程正在通过 cout 进行输出，但是我我不确定，这就是为什么我要在这里问。

But the input does not reach this function. I think the problem is that while input_func is waiting for input, other threads are making outputs over cout, but I'm not sure, that's why I'm asking here.

预先感谢！

推荐答案

我尝试了类似的操作（使用std :: thread代替（可能是）Posix线程）。这是代码和示例运行。为我工作;）

I tried something similar to you (using std::thread instead of (presumably) Posix threads). Here is the code and a sample run. Works for me ;)

#include <iostream>
#include <thread>
#include <chrono>
#include <string>

using std::cout;
using std::cin;
using std::thread;
using std::string;
using std::endl;

int stopflag = 0;

void input_func()
{
    while(true && !stopflag)
    {
        string input;
        cin >> input;
        cout << "Input: " << input << endl;
    }
}

void output_func()
{
    while(true && !stopflag)
    {
        std::this_thread::sleep_for (std::chrono::seconds(1));
        cout << "Output thread\n";
    }
}

int main()
{
    thread inp(input_func);
    thread outp(output_func);

    std::this_thread::sleep_for (std::chrono::seconds(5));
    stopflag = 1;
    outp.join();
    cout << "Joined output thread\n";
    inp.join();

    cout << "End of main, all threads joined.\n";

    return 0;
}


 alapaa@hilbert:~/src$ g++ --std=c++11 threadtzt1.cpp -lpthread -o     threadtzt1
alapaa@hilbert:~/src$ ./threadtzt1 
kOutput thread
djsölafj
Input: kdjsölafj
Output thread
södkfjaOutput thread
öl
Input: södkfjaöl
Output thread
Output thread
Joined output thread
sldkfjöak
Input: sldkfjöak
End of main, all threads joined.

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