code: def _user_thread_main(self, target):
          
          try:
              # Run user's code.
              return_code = target()
              # Assume good result (0 return code) if none is returned.
              if return_code is None:
                  return_code = 0
              # Call exit on the main thread when user code has finished.
              AppHelper.callAfter(lambda: sys.exit(return_code))
          except Exception as ex:
              # Something went wrong.  Raise the exception on the main thread to exit.
              AppHelper.callAfter(self._raise_error, sys.exc_info())
docs: Main entry point for the thread that will run user's code.