set realtime prio before executing launchfile

edit

For now the propopsed solution(s) won't be inplemented. @gvdhoorn gave the answer to my question, I'm positive this solves my problem. he refered to this example:

 std::ifstream realtime_file("/sys/kernel/realtime", std::ios::in);
  bool has_realtime;
  realtime_file >> has_realtime;
  if (has_realtime)
  {
    const int max_thread_priority = sched_get_priority_max(SCHED_FIFO);
    if (max_thread_priority != -1)
    {
      // We'll operate on the currently running thread.
      pthread_t this_thread = pthread_self();

      // struct sched_param is used to store the scheduling priority
      struct sched_param params;

      // We'll set the priority to the maximum.
      params.sched_priority = max_thread_priority;

      int ret = pthread_setschedparam(this_thread, SCHED_FIFO, &params);
      if (ret != 0)
      {
        ROS_ERROR_STREAM("Unsuccessful in setting main thread realtime priority. Error code: " << ret);
      }
      // Now verify the change in thread priority
      int policy = 0;
      ret = pthread_getschedparam(this_thread, &policy, &params);
      if (ret != 0)
      {
        std::cout << "Couldn't retrieve real-time scheduling paramers" << std::endl;
      }

      // Check the correct policy was applied
      if (policy != SCHED_FIFO)
      {
        ROS_ERROR("Main thread: Scheduling is NOT SCHED_FIFO!");
      }
      else
      {
        ROS_INFO("Main thread: SCHED_FIFO OK");
      }

      // Print thread scheduling priority
      ROS_INFO_STREAM("Main thread priority is " << params.sched_priority);
    }
    else
    {
      ROS_ERROR("Could not get maximum thread priority for main thread");
    }
  }

here are some other examples with a python implementation of the solution: https://python.hotexamples.com/exampl...