code: def _store_timestamp(self, timestamp):
          
          if getattr(self, 'first_timestamp', None) is None:
              self.first_timestamp = timestamp
              LOG.debug("Storing %d as the first timestamp of the trace file %s",
                      self.first_timestamp, self.filename)
docs: If not already saved, cache the first timestamp in the active trace
          file on the instance.