https://github.com/apache/airflow/blob/main/airflow/dag_processing/manager.py#L773
"""Returns the pipe for sending Callbacks to DagProcessorManager."""
        if not self._parent_signal_conn:
            raise ValueError("Process not started.")
        return self._parent_signal_conn
    def wait_until_finished(self) -> None:
        """Waits until DAG parsing is finished."""
        if not self._parent_signal_conn:
            raise ValueError("Process not started.")
        if self._async_mode:
            raise RuntimeError("wait_until_finished should only be called in sync_mode")
        while self._parent_signal_conn.poll(timeout=None):
            try:
                result = self._parent_signal_conn.recv()
            except EOFError:
                return
            self._process_message(result)
            if isinstance(result, DagParsingStat):
                
                
                return
    @staticmethod
    def _run_processor_manager(