[cffi-devel] Problem with SDL_Init using CFFI with Clisp in Windows 98

[James Bielman]

Jeremy Smith <jeremy at decompiler.org> writes:

> I'm posting this to the CFFI discussion group, I previously posted it to
> the Lisp Application Builder list.

(Sorry for the delay in approving your message; the list gets so much
spam I don't check it all that often.)

> What I'm getting to is, I read on comp.lang.lisp that the CFFI-based
> SDL module does not work on Windows 98 under Clisp. I just tested it
> on my Windows 98 laptop (P166 :-) and it says the same thing. "FFI:
> FOREIGN-LIBRARY-FUNCTION: No dynamic object named 'SDL_Init' in
> library :DEFAULT"

My first guess is that you are using an older version of CLISP that is
technically unsupported by CFFI.  What CLISP version are you using,
and do the SDL bindings work if you upgrade to the latest release?

IIRC, several releases ago, a feature was added to CLISP to look for
foreign symbols globally when the library is :DEFAULT, instead of only
in the C library.  Perhaps this is not working on Win9x... does this
work under NT/XP/whatever?

> I did a little bit of detective work:
>
> Clisp's top-level view shows the scope, at the time of the above error
> as (from src/cffi-clisp.lisp):
>
>       `(funcall
>         (load-time-value
>          (ffi::foreign-library-function
>           ,name (ffi::foreign-library :default)
>           nil (ffi:parse-c-type ',ctype)))
>         , at fargs))))
>
> The FFI documentation says nothing about a load-time-value, and
> ffi::foreign-library is not mentioned either. Strange!

In the CFFI design, the lowest level operator for calling a foreign
function is CFFI:FOREIGN-FUNCALL, which can be used for one-shot calls
to any C function with argument types known at compile-time:

  (foreign-funcall "puts" :string "Hello, world!" :void)

The DEFCFUN macro (in almost all Lisp implementations) expands into a
normal Lisp DEFUN that uses FOREIGN-FUNCALL to effect the actual
foreign function call.

The LOAD-TIME-VALUE in FOREIGN-FUNCALL is there to avoid resolving the
foreign function each time it is called; instead it is done once when
the fasl file is loaded.

> (ffi:def-call-out SDL_Init
>                   (:name "SDL_Init")
>                   (:library "sdl.dll")
>                   (:return-type ffi:int)
>                   (:arguments (flags Uint32)))

If this works with (:library :default) using the CLISP FFI (as I
understand it should, if sdl.dll has been loaded), then I would
expect it to work in CFFI as well.

James