[Gambas-user] Callbacks in Gambas (was Re: Signal management)

[Charlie Reinl]

Am Mittwoch, den 14.07.2010, 18:16 +0200 schrieb Benoît Minisini:
> > Benoît Minisini ha scritto:
> > >>>> Nice thing. But now I have a further question: is it possible to
> > >>>> implement generic callbacks in Gambas?
> > >>>> I mean - many libraries have functions where you specify a callback to
> > >>>> be called, like the glib function g_signal_connect(); it would be nice
> > >>>> to implement them, even partly, without resorting to write a gambas
> > >>>> component. May be that by using libffi it is possible to implement
> > >>>> them fully, but even a simple event could do. My problem now is that
> > >>>> using ALSA, I must poll continuously to see if some event is coming
> > >>>> in, wasting a lot of CPU and losing precision. With a callback if
> > >>>> would be much simpler...
> > >>>> 
> > >>>> I hope I have been clear enough.
> > >>>> 
> > >>>> Regards,
> > >>>> Doriano
> > >>> 
> > >>> It is possible, I will trying to do that. There is a lot of magic
> > >>> involved behind that, hopefully handled by the libffi library.
> > >>> 
> > >>> Alas, that library is not very well documented, so it will take a
> > >>> little time, and I'm not 100% sure it will work as expected.
> > >>> 
> > >>> Regards,
> > >> 
> > >> You should be happy with revision #3040.
> > >> 
> > >> Regards,
> > > 
> > > Some little information about callbacks:
> > > 
> > > If you want to use a Gambas function as a callback for an extern
> > > function, you just have to:
> > > 
> > > 1) Declare the extern function argument that will receive the function
> > > address as "Pointer".
> > > 
> > > 2) Use the Gambas function name when calling the extern function.
> > > 
> > > Note that you can use any private or public Gambas function. You can even
> > > use non-static methods: but beware that the object the method applies on
> > > is captured by the callback, and released at the end of the program
> > > only.
> > 
> > So if I have:
> > 
> >      int setcallback(callback_t yourfunc, int tag);
> > 
> > I must declare:
> > 
> >      EXTERN setcallback(afunc as pointer, tag as integer) as integer
> > 
> >      private sub mycallback(tag as integer)
> >      ...
> >      END
> >      ...
> >      setcallback(mycallback, 25)
> > 
> > Is it right?
> 
> Yes.
> 
> > 
> > > Waiting for your returns!
> > 
> > I must download this last revision of gambas, and compile it. I never
> > tried to do it. How do I download it? Possibly without SVN? Can it work
> > without QT4? I would prefer not to mess up my machine... (fanatic of
> > "stable" repositories...).
> > Can you advice?
> > 
> > Thanks,
> > Doriano
> > 
> 
> Read the top of the "dowload" page on the web site to know how to get the 
> latest trunk.
> 
> Sorry, but you have to install svn, qt4, and all the development tools and 
> package. This is explained on the wiki at the "compilation & installation" 
> page. Logically, unless you have a very old distribution, all "stable" 
> packages will be sufficient, and there is no reason you mess up your machine.
> 
> I can't say more without knowing your distribution.
> 
> Regards,
> 

Salut,

for svn, you can also go to "gambas homepage", click on "Browse Source
code" 
or direct to http://gambas.svn.sourceforge.net/viewvc/gambas/?view=tar 
and there go to trunk and use "Download GNU tarball"

-- 
Amicalement
Charlie