* AtomicReferenceArray of size 2^k. To map a user key into a stripe, we take a k-bit slice of the
   * user key's (smeared) hashCode(). The stripes are lazily initialized and are weakly referenced.
   */
  @VisibleForTesting
  static class SmallLazyStriped<L> extends PowerOfTwoStriped<L> {
    final AtomicReferenceArray<@Nullable ArrayReference<? extends L>> locks;