Re: Is gtkmm deleting stuff it shouldn't be deleting ??

[Murray Cumming <murrayc murrayc com>]

On Mon, 2013-11-04 at 17:58 +0000, John Emmas wrote:
> Allowing the window to close normally will call 
> 'gtk_widget_destroy()'

I wouldn't expect that. gtkmm Windows are not destroyed just because you
close them, though that can be the case with regular GTK+ windows.

>  which, in turn, calls 'gtk_object_destroy()' and 
> ultimately, 'g_object_run_dispose()'.  As expected, the gtkmm window 
> disappears from my screen.

And you think that the GObject and/or the C++ instance is freed here,
right? But how are you sure of that?

On Linux, valgrind would tell us about use of freed memory.

>   Now we reach this line:-
>
>                  delete mainWnd;  // <--- crashes here !
>
> The above line invokes the d'tor for Gtk::Window.  The d'tor calls 
> 'Gtk::Window::destroy_()' which then calls 
> 'Gtk::Window::_destroy_c_instance()'.  Note that 
> 'Gtk::Window::_destroy_c_instance()' contains some warnings about 
> ensuring that 'C' and C++ objects get destroyed in the correct 
> sequence.  Once inside 'Gtk::Window::_destroy_c_instance()' we hit
> this 
> code:-
>
>          if (!gobject_disposed_)
>          {
>                //Windows can not be unrefed. They are "self-owning".
>                gtk_object_destroy(object);
>          }
>
> and bingo!  We call 'gtk_object_destroy()' all over again on an
> object 
> that's already been destroyed!  The crash actually occurs in 
> 'g_object_run_dispose()' at this line:-
>
>          G_OBJECT_GET_CLASS (object)->dispose (object);
>
> Effectively, we're trying to get the class of an object that GTK+
> just 
> destroyed for us.  Hope you can make sense of all that!

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com
www.openismus.com