def startReactor(self):
        """
        Register C{self._whenRunning} with the reactor so that it is called
        once the reactor is running, then start the reactor.
        """
        self._reactor.callWhenRunning(self.whenRunning)

        self._log.info("Starting reactor...")
        self._reactor.run()

        Register C{self._whenRunning} with the reactor so that it is called
        once the reactor is running, then start the reactor.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/runner/_runner.py