} else if (getState() == COMPLETING) {
          // If some other thread is currently completing the future, block until
          // they are done so we can guarantee completion.
          acquireShared(-1);
        }
        return doCompletion;
      }
    }

    static final CancellationException cancellationExceptionWithCause(
        @Nullable String message, @Nullable Throwable cause) {