How to fill Gtk::TreeModelColumn with a large dataset without locking up the application

Question

I need to fill in a large (maybe not so much - several thousands of entries) dataset to a Gtk::TreeModelColumn. How do I do that without locking up the application. Is it safe to put the processing into separate thread? What parts of the application do I have to protect with a lock then? Is it only the Gtk::TreemodelColumn class, or Gtk::TreeView widget it is placed in, or maybe even surrounding frame or window?

Answer 1

There are two general approaches you could take. (Disclaimer: I've tried to provide example code, but I rarely use gtkmm - I'm much more familiar with GTK in C. The principles remain the same, however.)

One is to use an idle function - that runs whenever nothing's happening in your GUI. For best results, do a small amount of calculation in the idle function, like adding one item to your treeview. If you return true from the idle function, then it is called again whenever there is more processing time available. If you return false, then it is not called again. The good part about idle functions is that you don't have to lock anything. So you can define your idle function like this:

bool fill_column(Gtk::TreeModelColumn* column)
{
    // add an item to column
    return !column_is_full();
}

Then start the process like this:

Glib::signal_idle().connect(sigc::bind(&fill_column, column));

The other approach is to use threads. In the C API, this would involve gdk_threads_enter() and friends, but I gather that the proper way to do that in gtkmm, is to use Glib::Dispatcher. I haven't used it before, but here is an example of it. However, you can also still use the C API with gtkmm, as pointed out here.