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

[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,

-- 
Benoît Minisini