* @Nullable X>, then users might pass a TypeParameter<Y>, where Y is a subtype of X, while still
   * passing a TypeToken<X>. This would be invalid. Maybe we could accept a TypeParameter<@PolyNull
   * 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

  /**
   * Marks the given node as 'deleted' (null waiter) and then scans the list to unlink all deleted
   * nodes. This is an O(n) operation in the common case (and O(n^2) in the worst), but we are saved
   * by two things.
   *
   * <ul>
   *   <li>This is only called when a waiting thread times out or is interrupted. Both of which
   *       should be rare.
   *   <li>The waiters list should be very short.
   * </ul>
   */

    Collections.addAll(set, elements);
    return set;
  }

  /**
   * Creates a <i>mutable</i> {@code HashSet} instance containing the given elements. A very thin
   * convenience for creating an empty set then calling {@link Collection#addAll} or {@link
   * Iterables#addAll}.
   *
   * <p><b>Note:</b> if mutability is not required and the elements are non-null, use {@link

   * the computation -- makes sense, and if we don't convert it, the user still has to write a
   * try-catch block.
   *
   * If you think you would use this method, let us know. You might also look into the
   * Fork-Join framework: http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html
   */