private void OnProductChanged(object sender, ProductChangeEventArgs e)
 {
     try
     {
         _callback.OnUpdate(e.Product);
     }
     catch (CommunicationException)
     {
         // noop
     }
 }
 private async void OnProductChanged(object sender, ProductChangeEventArgs e)
 {
     await _subscriberStream.WriteAsync(e.Product);
 }