} // else no check necessary, all index values are valid
      ArrayReference<? extends L> existingRef = locks.get(index);
      L existing = existingRef == null ? null : existingRef.get();
      if (existing != null) {
        return existing;
      }
      L created = supplier.get();
      ArrayReference<L> newRef = new ArrayReference<>(created, index, queue);
      while (!locks.compareAndSet(index, existingRef, newRef)) {