in lib/src/stream_queue.dart [389:401]
Future? cancel({bool immediate = false}) {
_checkNotClosed();
_isClosed = true;
if (!immediate) {
var request = _CancelRequest<T>(this);
_addRequest(request);
return request.future;
}
if (_isDone && _eventQueue.isEmpty) return Future.value();
return _cancel();
}