anchor.diff:    Stream get _onWorkerReady => _readyController.stream;
   
     Future _startIsolate() {
  -    Completer completer = new Completer();
       _receivePort.listen((arg) {
         if (_sendPort == null) {
           _sendPort = arg;
  
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:   _ping(Completer completer) {
      _sendPort.send(_serviceCallId++);
    }
  
    Future pong(int id) {
      Completer completer = _serviceCallCompleters[id];
      _serviceCallCompleters.remove(id);
      completer.complete("pong");
    }
  
  }
  
  