}

  /**
   * Marks the given step final, waits for it to be finished, and returns the value.
   *
   * @throws ExecutionException if the step failed
   * @throws CancellationException if the step was cancelled
   */
  abstract <T> T getFinalValue(ClosingFuture<T> closingFuture) throws ExecutionException;

  }

  /**
   * Marks the given step final, waits for it to be finished, and returns the value.
   *
   * @throws ExecutionException if the step failed
   * @throws CancellationException if the step was cancelled
   */
  abstract <T> T getFinalValue(ClosingFuture<T> closingFuture) throws ExecutionException;