* the given future (if available).
   */
  final void maybePropagateCancellationTo(@CheckForNull Future<?> related) {
    if (related != null & isCancelled()) {
      related.cancel(wasInterrupted());
    }
  }

  /** Releases all threads in the {@link #waiters} list, and clears the list. */
  private void releaseWaiters() {