/**
   * Number of cache access operations that can be buffered per segment before the cache's recency
   * ordering information is updated. This is used to avoid lock contention by recording a memento
   * of reads and delaying a lock acquisition until the threshold is crossed or a mutation occurs.
   *
   * <p>This must be a (2^n)-1 as it is used as a mask.
   */
  static final int DRAIN_THRESHOLD = 0x3F;

  /**

   * backing sets do. Contains methods to copy the data into a new set which will then remain
   * stable. There is usually no reason to retain a reference of type {@code SetView}; typically,
   * you either use it as a plain {@link Set}, or immediately invoke {@link #immutableCopy} or
   * {@link #copyInto} and forget the {@code SetView} itself.
   *
   * @since 2.0
   */

   * X> if we support such a thing? It would be weird or misleading for users to be able to pass
   * `new TypeParameter<@Nullable T>() {}` and have it act as a plain `TypeParameter<T>`, but
   * hopefully no one would do that, anyway. See also the comment on TypeParameter itself.
   *
   * TODO(cpovirk): Elaborate on this / merge with other comment?
   */