* known yet. That result, though not yet known, cannot be overridden by a call to a {@code set*}
   * method, only by a call to {@link #cancel}.
   *
   * <p>Beware of completing a future while holding a lock. Its listeners may do slow work or
   * acquire other locks, risking deadlocks.
   *
   * @param throwable the exception to be used as the failed result

      return "setFuture=[" + delegate + "]";
    }
    return null;
  }

  private void addDoneString(StringBuilder builder) {
    try {
      V value = getDone(this);
      builder.append("SUCCESS, result=[").append(value).append("]");
    } catch (ExecutionException e) {
      builder.append("FAILURE, cause=[").append(e.getCause()).append("]");
    } catch (CancellationException e) {
      builder.append("CANCELLED");