* opportunistically, just to simplify some locking and avoid separate construction.
   */
  @SuppressWarnings("serial") // This class is never serialized.
  abstract static class Segment<
          K, V, E extends InternalEntry<K, V, E>, S extends Segment<K, V, E, S>>
      extends ReentrantLock {

    /*

   * opportunistically, just to simplify some locking and avoid separate construction.
   */
  @SuppressWarnings("serial") // This class is never serialized.
  abstract static class Segment<
          K, V, E extends InternalEntry<K, V, E>, S extends Segment<K, V, E, S>>
      extends ReentrantLock {

    /*