Starts the background thread.

        Additionally, this registers a handler for process exit to attempt
        to send any pending log entries before shutdown.

def start(self):
        """Starts the background thread.

        Additionally, this registers a handler for process exit to attempt
        to send any pending log entries before shutdown.
        """
        with self._operational_lock:
            if self.is_alive:
                return

            self._thread = threading.Thread(
                target=self._thread_main, name=_WORKER_THREAD_NAME
            )
            self._thread.daemon = True
            self._thread.start()
            atexit.register(self._main_thread_terminated)