https://github.com/apache/airflow/blob/main/airflow/dag_processing/manager.py#L773
"""
        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: