Re: Calling Scheme from C and Garbage Collection

[Greg Harvey <Greg.Harvey@thezone.net>]

Etienne Bernard <eb@via.ecp.fr> writes:

> Hello
> 
> I'm using Guile from my C program, and I use scm_make_regexp to create a
> regexp SCM object:
> 
> SCM r = scm_make_regexp(regex,
>                         gh_list(gh_lookup("regexp/icase"),
>                                 SCM_UNDEFINED));
> 
> I get strange errors when I call scm_regexp_exec which makes me think that
> the regexp got garbage collected somewhere:
> 
> ERROR: In procedure regexp-exec:
> ERROR: Wrong type argument in position 1: #<unknown-type (0x7f . 
> 0x4024a480) @ 0x4024a488>
> 
> (first argument of scm_regexp_exec was r)
> 
> Is this error really related to garbage collection, and what is then the
> means to protect my newly created object ?

Looks like it could be. What happens sometimes is that the compiler is
optimizing away the SCM value, so that the gc can miss it. What you
can do is scm_remember(&r), or, if the function returns something,
call return scm_return_first(something, r) (these are both defined in
gc.c; they don't do anything, but the presence of r later on means
that the compiler can't optimize it away).

> Where can I get more information on Guile 1.3 garbage collection ?

gc.c ;) Actually, the documentation that comes with scm is also pretty
good, since guile isn't that far removed from scm in some places; some
of the problems that can come up are addressed in the extending scm
section. I'm not sure if much about the gc is present in the partial
documentation you can get via cvs.

I have some notes up on the generational gc that I'm working on at

http://home.thezone.net/~gharvey/guile/guile.html 

that sort of skirt around the current implementation, but there isn't
really anything on the hard implementation details of the current gc
there... so maybe it's not that useful, but shameless plugs are a bit
of fun :)

-- 
Greg