Re: memory leaks destroying widgets

[Owen Taylor <otaylor redhat com>]

Owen Taylor <otaylor@redhat.com> writes:

> judd montgomery <judd@engineer.com> writes:
> 
> > I have an application in which I create lots of widgets.  clists, text
> > boxes, entries, etc.  Then I destroy the box that they are all packed
> > into using gtk_widget_destroy() and then I redraw more widgets, and then
> > I repeat this process.  Why do I have memory leaks?  Should I be doing
> > something more?
> 
> That should work. Without more information it is hard
> to say why you are leaking memory.
> 
> (When I say that it works, it works assuming that box
>  is packed into a toplevel.
> 
>   box = gtk_hbox_new (FALSE, 0);
>   label = gtk_label_new ("Hi");
>   gtk_container_add (GTK_CONTAINER (box), label);
>   gtk_widget_destroy (box);
> 
>  Leaks both the box and the label. 
> 
>  A widget is created with a reference count of 1; this
>  reference count is taken over by a parent when you add
>  it to a parent.)

I was asked for some more information on this. 
The detailed source of information on memory management
issues is docs/refcounting.txt; I'll just summarize
briefly here.

The basic idea is that a widget is created in a special
FLOATING state with a reference count of 1. The FLOATING
flag means that the initial reference count is 
"available for adoption". When a widget is added to
a container, the container checks the FLOATING flag, 
and if it is set, takes over the reference count and
clears the flag (this involves calling gtk_widget_sink().)

In the above example, the FLOATING flag is still set
on 'box' when it is destroyed, and its reference
count remains at 1, so box is not destroyed.

(Actually, I was wrong when I said it leaks both the
box and the label; the memory for the label does
get freed).

Toplevel widgets, such as GtkWindows, are special in that
they automatically sink themselves. For a toplevel
window, calling gtk_widget_destroy() causes the
initial reference count to be released.

For more information, take a look at docs/refcounting.txt
or Havoc Pennington has information about this
in his book _GTK+/Gnome Application Development_.

Regards,
                                        Owen