Here it is. Use threads. Email questions.
Using threads, you would have the same problem as with calling Gtk::Main::iteration() periodically: The GUI remains fully responsive.
What about disabling any widgets you don't want the user to interact with during your calculation via Gtk::Widget::set_sensitive()? The Window as such remains responsive to the operating system (e.g. Windows would not say that it "does not react" anymore) and the user cannot click any buttons. Additionally, the user has some more feedback that tells him that there is a calculation going on and he currently cannot interact with the application.
- Armin