*
   * It is possible for a Cell to become unused when threads that
   * once hashed to it terminate, as well as in the case where
   * doubling the table causes no thread to hash to it under
   * expanded mask.  We do not try to detect or remove such cells,
   * under the assumption that for long-running instances, observed
   * contention levels will recur, so the cells will eventually be

   *
   * It is possible for a Cell to become unused when threads that
   * once hashed to it terminate, as well as in the case where
   * doubling the table causes no thread to hash to it under
   * expanded mask.  We do not try to detect or remove such cells,
   * under the assumption that for long-running instances, observed
   * contention levels will recur, so the cells will eventually be

   *
   * It is possible for a Cell to become unused when threads that
   * once hashed to it terminate, as well as in the case where
   * doubling the table causes no thread to hash to it under
   * expanded mask.  We do not try to detect or remove such cells,
   * under the assumption that for long-running instances, observed
   * contention levels will recur, so the cells will eventually be