"""Heartbeat DAG file processor and restart it if we are not done."""
        if not self._parent_signal_conn:
            raise ValueError("Process not started.")
        if self._process and not self._process.is_alive():
            self._process.join(timeout=0)
            if not self.done:
                self.log.warning(
                    "DagFileProcessorManager (PID=%d) exited with exit code %d - re-launching",
                    self._process.pid,
                    self._process.exitcode,
                )
                self.start()
        if self.done:
            return
        parsing_stat_age = time.monotonic() - self._last_parsing_stat_received_at
        if parsing_stat_age > self._processor_timeout.total_seconds():
            Stats.incr("dag_processing.manager_stalls")
            self.log.error(
                "DagFileProcessorManager (PID=%d) last sent a heartbeat %.2f seconds ago! Restarting it",
                self._process.pid,
                parsing_stat_age,
            )
            reap_process_group(self._process.pid, logger=self.log)
            self.start()
    def _sync_metadata(self, stat):