handle waitkey in multi-thread application

edit

I have a multi-threading application written in C++ with Qt5.7 and OpenNI. It has a main thread that starts a second thread which capture frame from a .oni recording file (asus xtion pro live) does some processing and through the Qt signal-slot mechanism pass the frame to the main thread, which display it using imshow(). What I want to do is to implement a pause key, so pressing for example 'p' the processing pause. I am thinking of something like this:

void Camera::run(){
  while(!cameraStop && this->device.isValid())
    {
      try {
        if (!buttonPause) {
            getFrame();
            process();
            emit sigFrameImageReady(frame);
            if (cv::waitKey(1)==112){
              setButtonPause(!(getButtonPause()));
            }
         }

       }
      catch(std::exception &ex) {
         std::cerr << "getFrame()" << ex.what() << std::endl;
      }
    }
}

In this way it doesn't work, I think that's because the frame is displayed by another thread (the main one), the waitKey() here simply blocks the entire process, but if I put it in the main thread, just after imshow() in this way:

void Process::FrameImageReady(cv::Mat FrameImage)
{
  if (modedebug)
    cv::imshow("bgr", FrameImage);
  if (cv::waitKey(10)==112){
    cam->setButtonPause(!(getButtonPause()));
  }
}

waitkey seems to be ignored (image displaying works fine).. any idea?