"""
        Should only be used when launched DAG file processor manager in sync mode.
        Send agent heartbeat signal to the manager, requesting that it runs one
        processing "loop".
        Call wait_until_finished to ensure that any launched processors have
        finished before continuing
        """
        if not self._parent_signal_conn or not self._process:
            raise ValueError("Process not started.")
        if not self._process.is_alive():
            return
        try:
            self._parent_signal_conn.send(DagParsingSignal.AGENT_RUN_ONCE)
        except ConnectionError:
            
            
            pass
    def get_callbacks_pipe(self) -> MultiprocessingConnection: