Re: [Caml-list] Save callbacks from OCaml to C

["Christoph Höger" <christoph.hoeger@tu-berlin.de>]

Am 03.02.2016 um 14:49 schrieb Jeremie Dimino:
> CAMLparam0 is for when you have no [value] arguments but have some local
> [value] variables. CAMLlocalN must be preceded by a CAMLparamY, that's
> why you need the CAMLparam0.

Thanks. I wasn't sure about that, since I tried before and my stack
values were overwritten (I assumed it was the GC at that time).

> So if the GC ends up moving [g], it needs to know that it must update
> [user_data->g] to point to the new location.

Even more subtle. user_data was a pointer to the body of a custom
allocated block. My huge mistake was to use the custom_val directly
(i.e. I allocated n bytes and passed around the pointer to these n
bytes). As it turns out, the GC may move a custom block by memcopying
its body. So in that body I needed pointers to allocated data not the
allocated data itself.

Thanks again!

-- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de