anchor.diff:    _ping(Completer completer) {
       _sendPort.send(_serviceCallId++);
     }
  +
  +  Future pong(int id) {
  +    Completer completer = _serviceCallCompleters[id];
  +    _serviceCallCompleters.remove(id);
  +    completer.complete("pong");
  +  }
  +
   }
   
  
positive.code:     });
  
      Isolate.spawnUri(Uri.parse(_workerPath), [], _receivePort.sendPort);
  
      return completer.future;
    }
  
    Future pong(int id) {
      Completer completer = _serviceCallCompleters[id];
      _serviceCallCompleters.remove(id);
      completer.complete("pong");
    }
  
    Future<String> ping() {
  
negative.code:   Stream get _onWorkerReady => _readyController.stream;
  
    Future _startIsolate() {
      _receivePort.listen((arg) {
        if (_sendPort == null) {
          _sendPort = arg;
  