anchor.diff:        if (result != null) {
           // TODO return value ?
           _ttyFd = -1;
  -        _state = CLOSED;
           completer.complete(true);
         } else {
           completer.completeError("Unexpected error");
  
positive.code: 
    Future<bool> close(){
      // TODO check OPEN
      _state = CLOSING;
      var completer = new Completer<bool>();
      var replyPort = new RawReceivePort();
      _servicePort.send([replyPort.sendPort, "close", _ttyFd]);
  
negative.code:       if (result != null) {
          if(result >= 0){
            _ttyFd = result;
             completer.complete(true);
          } else {
            completer.completeError("Cannot open portname=$portname");
          }
  