code: def _on_call_service_msg(self, msg):
          
          if not msg.is_dead:
              th = threading.Thread(target=self._service_stub_main, args=(msg,))
              th.start()
docs: Stub service handler. Start a thread to import the mitogen.service
          implementation from, and deliver the message to the newly constructed
          pool. This must be done as CALL_SERVICE for e.g. PushFileService may
          race with a CALL_FUNCTION blocking the main thread waiting for a result
          from that service.