code: def mark_in_progress(self, rr_id: str, rr_size: int) -> None:
          
          try:
              makedirs(join(self._dir_tails_sentinel, rr_id), exist_ok=False)
          except FileExistsError:
              LOGGER.warning('Rev reg %s construction already in progress', rr_id)
          else:
              open(join(self._dir_tails_sentinel, rr_id, '.{}'.format(rr_size)), 'w').close()
docs: Prepare sentinel directory for revocation registry construction.
  
          :param rr_id: revocation registry identifier
          :rr_size: size of revocation registry to build