Re: [Vala] Setting up a GLib main loop with custom Sources with Vala 0.11.7

[Abderrahim Kitouni <a kitouni gmail com>]

Hello,
(See below for my attempts at improving your workarounds)

                      في ن، 28-03-2011 عند 06:23 -0500 ، كتب Jim Peters:
> For reference, I have a Glib main loop with custom Source instances
> working now, in case anyone else needs to do it.  With the 0.11.7
> compiler I had to make a number of work-arounds for compiler bugs and
> limitations, and I had to hack my glib VAPI file.  It is not ideal but
> it works (although I haven't checked for leaks yet).  Hopefully in
> later versions these hacks won't be necessary.
>
> Probably this isn't the best way of solving these problems, but since
> I know no better ...
>
>
> - Change SourcePrepareFunc in the VAPI to use 'int*' instead of 'out
>   int' for the timeout, and change the calling code accordingly:
>
>         [CCode (has_target = false)]
>         public delegate bool SourcePrepareFunc (Source source, int* timeout_);
>
>   This works around bug 645838.  Using 'out int' would be better in
>   the long run.

Another (better IMO) workaround is not to use a lambda expression and
use a method instead.

> - Add a constructor for SourceFuncs in the VAPI, and implement
>   g_source_funcs_new and g_source_funcs_free in C:
> [...]
>   Note that GLib expects SourceFuncs to be static data, i.e. it
>   doesn't copy it or do any ownership stuff.  So the caller has to
>   make sure it stays around as long as the Source remains active.

That's not right, we can't have an additional C code other than what
there is in glib. You can probably make it a struct instead: it will be
allocated/freed automatically (as it is a value type), and could then be
statically allocated.

> - Pass a 'guessed' size value to the Source superclass constructor.
>   The Source constructor wants to know the size of the object
>   constructed.  The code 'sizeof(MySource)' gives the size of a
>   pointer, not the size of the structure, so it doesn't seem possible
>   to get this value in Vala.  So I pass 256 for now which is more than
>   enough.

A workaround I see here (but that would still be a hack), is to have a
new constant named SIZE in GLib.Source defined as (untested):

        [CCode (cname="sizeof(GSource)"]
        public const int SIZE;

and use that in the constructor (assuming you don't need additional
fields in your source).

HTH,
Abderrahim