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