code: def HeartBeat(self):
      
      # In prod, self.job.lifetime is guaranteed to always be set, and is
      # always equal to self.__class__.lifetime. Some tests however, do not
      # set the job lifetime, which isn't great.
      if self.allow_overruns or not self.job.lifetime:
        return
  
      runtime = rdfvalue.RDFDatetime.Now() - self.run_state.started_at
      if runtime > self.lifetime:
        raise LifetimeExceededError(
            "Cronjob run has exceeded the maximum runtime of %s." % self.lifetime)
docs: Terminates a cronjob-run if it has exceeded its maximum runtime.
  
      This is a no-op for cronjobs that allow overruns.
  
      Raises:
        LifetimeExceededError: If the cronjob has exceeded its maximum runtime.