Re: Overhead of type casting when using GObject system

[Lanoxx <lanoxx gmx net>]

Hi Emanuele,

thanks for the comprehensive response.
On 10/02/13 12:08, Emmanuele Bassi wrote:
> On 9 February 2013 12:43, Lanoxx <lanoxx gmx net> wrote:
> > > However those cast checks can be disabled at compile time removing the
> > > overhead, so GTK_WIDGET(foo) would be equivalent to (GtkWidget *) foo.
> > Ah thats good to know. But still I believe that most applications that are
> > shipped with gnome are not compiled that way.
> stable releases of gtk automatically disable cast checks for internal
> usage; it's actually pretty easy to do, you just need to define
> G_DISABLE_CAST_CHECKS symbol before including glib-object.h.
>
> disabling cast checks is usually the result of performance profiling,
> tho, so it should only be used if you have profiled your application
> code and verified that type casting is high on the profiles; there are
> also various ways to avoid that, by using ancillary values and the
> correct type to minimize casting, before a blanket type cast check
> disable.
So do I understand if correctly that the cast checks can be disabled 
invididually per compiled object file, e.g. before linking them 
together? An all I have to do is adding these lines:

#define G_DISABLE_CAST_CHECKS
#include <glib/gobject.h>

in my source file?

> > So what overhead does that
> > actually create.
> on a typical laptop, you can do various milions of type checks per
> second; there is a type check performance test in the GObject test
> suite: http://git.gnome.org/browse/glib/tree/tests/gobject/performance.c
> - you can compile glib and the performance test yourself, and do a
> quick check on the expected upper bound of the numbers of type checks.
>
> in my professional experience, you'll have many issues before the type
> checks will raise to a relevant portion of the performance profile.
> once you get there, you can clean up and reorganize your code before
> deciding whether or not to build your stack and your application
> without type checks.
Great, good to know.
> ciao,
>   Emmanuele.
Regards
Lanoxx