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

[Brian Lu Sun COM]

Hi, Markku,

Thanks a lot for your help.

I did some further investigation on this issue.  I have two questions on 
this issue:

1. The object created by gtk_invisible_new() is not "floating". 

Here is a snippet from gtk+-2.12.5/tests/testselection.c

init_atoms();
 selection_widget = gtk_invisible_new ();
*  m = GTK_OBJECT_FLOATING(selection_widget);  //***
 dialog = gtk_dialog_new ();
 gtk_widget_set_name (dialog, "Test Input");

The black line (marked with "**") is added by me.
When I run testselection, "m" is set to 0 instead of 1.  Which means the 
selection_widget is not "floating".
right or I used a wrong macro?

2. How to release an object created by gtk_invisible_new()?
Look at following snippets:

  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);
   }

  nsLookAndFeel::~nsLookAndFeel()
  {
      //  gtk_widget_destroy(mWidget);
      gtk_widget_unref(mWidget);
  }

If I comment out the black line (marked with "**"), the mWidget 
reference count is 1 as expected,
but when unref  it in nsLookAndFeel::~nsLookAndFeel,  thunderbird will 
crash.
It looks like that I can't us gtk_widget_unref() on the object returned 
by gkt_invisible_new().

So my question is how to "free" an object returned by gtk_invisible_new()?

Thanks a lot

Brian


Markku Vire wrote:
> Hi,
>
> The reference that is returned by gtk_invisible_new is not owned by the
> caller. If one tries to unref it, it's an immediate memory corruption.
>
> When a toplevel widget is concerned, the things go like the following:
>  * New floating GtkWidget is created (not owned by anyone).
>  * GTK library takes ownership of the toplevel (calling
>    g_object_ref_sink). Floating reference is converted to normal one.
>  * Widget pointer is returned (refcount = 1, owner = gtk).
>
> So, in the code you attached gtk_object_ref increases the reference
> count to 2, gtk_object_sink does nothing (since it not floating any
> more).
>
> Later gtk_widget_unref decreases refcount back to 1, but there is still
> one reference left (owned by gtk). Trying to remove it by g_object_unref
> is a bug (as you noticed). The way to ask GTK to release the last
> reference is to call gtk_widget_destroy.
>
> If you are just interested about the GtkStyle object, you could try
> using gtk_rc_get_style_by_paths for example? 
>
> Cheers,
>
> -Markku-
>
> On Fri, 2008-01-11 at 16:53 +0800, 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
> >
> > 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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> > gtk-devel-list mailing list
> > gtk-devel-list gnome org
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>
>