CODEWITHSUNDEEP
c++multithreading
I Need Help
I Need Help

Reputation: 39

Multithreading a while loop in c++

I've started c++ (coming from a c# background), and in my program I need to run a while true loop, but since it is an imgui program the ui freezes up completely since I'm using Sleep() in the loop. I need to create a new thread but everything I've found online is just

std::thread nThread(Method);
nThread.join();

Now, the issue with this is it doesn't work at all since, I'm assuming, it's a while loop that's always running. I want to do the c++ equivalent of Thread thread = new Thread(method) and thread.Start(); in c#. If anyone can help me, I'd appreciate it.

Upvotes: 1

Views: 2953

Answers (4)

user20874672
user20874672

Reputation: 1

There is a way you can approach this and is using std::future and std::async with std::launch::async mode and throwing the function with the loop there.

std::future allows you to run a thread in the background and then after running give back the control to the parent thread so the program's flow can go as normal.

so you could have a boolean for the while and when std::future gives you back the control then you could modify this bool in the parent or main thread.

Upvotes: 0

ventsyv
ventsyv

Reputation: 3532

Try a simple example and work from there.

void myFunc()
{
    try 
    { 
       int x = 0;
       while (x < 10)
       {
          sleep(1000);
          std::cout<<"Thread is running"<<std::endl;
          x++;
       }
   }
   catch(Interrupted_Exception&) {
        cout << "Caught Interrupted_Exception" << endl;
   }
}

int main()
{
   std::cout<<"Starting main"<<std::endl;
   std::thread nThread(myFunc);
   
   std::cout<<"Thread is running. Waiting for it to complete"<<std::endl;

   nThread.interrupt();//in case the thread is sleeping
   nThread.join();
  
   std::cout<<"All done. Exiting"<<std::endl;
   return 0;
}

Join means that the main thread has to wait for the worker thread. It's a way to ensure that the worker thread terminates before the caller. You only want to do that when you are terminating the program, in your case when the GUI is being close. Since at that time you want to tell the worker thread to stop right away, you call interrupt() on tell it to stop sleeping.

In the example, you can comment out the interrupt call so that the worker thread runs to completion.

Upvotes: 1

ivan.ukr
ivan.ukr

Reputation: 3551

There is no direct equivalent of that in the standard C++ library. When you use std::thread, the new thread starts immediately. You can simulate delayed start behaviour by making the thread stuck on a locked in advance mutex, then release mutex when you want the thread action to run actually. Aftwerwards you have to either join the thread or make it detached, otherwise std::thread destructor will throw an exception. If you are on Windows, you can try to use Windows API directly (CreateThread() with flag CREATE_SUSPENDED, then ResumeThread() and finally posssibly TerminateThread() - if thread has sort of endless loop which never terminates in itself).

Upvotes: 0

Solomon Slow
Solomon Slow

Reputation: 27115

t.join() waits for thread t to die. If you don't want the method that started the thread to wait for it, then don't join() it.

But note! The C++ library will get angry with you if you allow the thread object to be destroyed while the thread still is running. (The destructor will throw an exception.) If you want to tell the library, "Shut up! I know what I'm doing," you can detach the thread from the object. But usually it's a cleaner design if you can arrange for the object to live for as long as you need the thread to run.

Upvotes: 6

Related Questions