Re: Can I use gtk_widget_unref() to releasetthe object created by gtk_invisible_new()?

["Brian J. Tarricone" <bjt23 cornell edu>]

(This is a bit better suited to gtk-app-devel-list, but...)

Brian Lu wrote:
> Thanks a lot for your explanation.  But look at following snippet from 
> firefox latest code base:
>     void InitWidget() {
>         mWidget = gtk_invisible_new();
>         gtk_object_ref(GTK_OBJECT(mWidget));
>         gtk_object_sink(GTK_OBJECT(mWidget));
>         gtk_widget_ensure_style(mWidget);
>         mStyle = gtk_widget_get_style(mWidget);
>     }
> see 
> http://lxr.mozilla.org/seamonkey/source/widget/src/gtk2/nsLookAndFeel.h#77
> and
> nsLookAndFeel::~nsLookAndFeel()
> {
>     //  gtk_widget_destroy(mWidget);
>     gtk_widget_unref(mWidget);
> }
> see 
> http://lxr.mozilla.org/seamonkey/source/widget/src/gtk2/nsLookAndFeel.cpp#78

Don't use Firefox as an example of how to best use gtk.  They do some 
rather arcane things to implement their gtk backend that should never be 
done in normal gtk-only applications.

In most normal apps, you never need to _ref() or _unref() widgets.  You 
just create them, add them to a container, and call gtk_widget_destroy() 
on the toplevel container when you want to get rid of them all.

You'd only use ref/unref if you want to keep widgets alive while 
reparenting them (that is, removing them from one container and then 
adding them to another).

Because of how gtk's memory management policy was designed, when you 
create a widget, you don't own a reference to it.  There's a so-called 
'floating reference' that no one owns.  When you add a widget to a 
container, the container takes ownership of the widget and removes the 
floating reference.  Calling _unref() yourself would be releasing a 
reference that isn't yours to release.

	-brian

> I find mWidget is leaked (detected by using libumem.so provided by solaris).
>
> I don't understand why calling gtk_object_ref() to increase mWidget 
> reference count. 
> This causes mWidget's reference count to be 2 and gtk_widget_unref() in 
> deconstructor decreases it to 1.
>
> Thanks
>
> Brian
>
>
>
> Markku Vire wrote:
> > Hi,
> >
> > The caller doesn't own the returned reference in case of any gtk_*_new
> > functions, but the results are floating references (they are removed
> > once somebody calls gtk_object_sink). This is different from normal
> > GObjects. So, unreffing the returned value causes practically a double
> > free.
> >
> > gtk_widget_destroy in turn runs dispose, ie. asks widget to drop
> > references to other widgets. Dropping external references usually causes
> > somebody else to drop the last reference to your widget, so it
> > efectively gets destroyed. In case of toplevels some global window list
> > is holding the reference.
> >
> > Calling gtk_widget_destroy without taking ownership a a widget is
> > usually a bug that causes a memory leak, but this is not the case here,
> > since we are talking about a toplevel.
> >
> > Cheers,
> >
> > -Markku- 
> >
> > On Wed, 2008-01-09 at 17:39 +0800, Brian Lu wrote:
> >   
> > > Hi, experts,
> > >
> > > I found following codes will crash in gnome 2.21 environment:
> > >
> > >   ...
> > >   GtkWidget *foo = gtk_invisible_new();
> > >   gtk_widget_unref(foo);
> > >   ...
> > >
> > > But it works well if gtk_widget_unref() is replaced with 
> > > gtk_widget_destroy().
> > >
> > > Does that mean that we can't use gtk_widget_unref() on such object and 
> > > we can only
> > > use gtk_widget_destroy() to release it?
> > >
> > > Thanks
> > >
> > > Brian
> > > _______________________________________________
> > > gtk-devel-list mailing list
> > > gtk-devel-list gnome org
> > > http://mail.gnome.org/mailman/listinfo/gtk-devel-list
> > >     
> >   
>
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