* clearListeners.
         */
        Runnable task = requireNonNull(curr.task);
        if (task instanceof SetFuture) {
          SetFuture<?> setFuture = (SetFuture<?>) task;
          // We unwind setFuture specifically to avoid StackOverflowErrors in the case of long
          // chains of SetFutures
          // Handling this special case is important because there is no way to pass an executor to