[cffi-devel] foreign-alloc

[Martin Simmons]

Hi there,

I've been lurking here for a couple of weeks to see how cffi is progressing.
It looks good so far!


>>>>> On Sun, 4 Sep 2005 20:03:54 +0100, Luis Oliveira <luismbo at gmail.com> said:

  Luis>    CFFI> (foreign-alloc :int :initial-contents #(1 2 3))
  Luis>    #<A Mac Pointer #x1022E0>
  Luis>    CFFI> (loop for i from 0 below 3
  Luis>                collect (mem-ref * :int i))
  Luis>    (1 2 3)

  Luis>    ;; Another note: what should should be in (mem-ref ** :int 3)?
  Luis>    ;; Zero? Ie. Should these previous two calls to foreign-alloc
  Luis>    ;; allocate 3*sizeof(int) or 4*sizeof(int) bytes? Lispworks seems to
  Luis>    ;; do the latter.

LispWorks allocates 3*sizeof(int), but the C heap manager might round this up
to 4.  (mem-ref ** :int 3) should be expected to give a random result or a
crash.


  Luis>    CFFI> (foreign-alloc :string :initial-element "foo")
  Luis>    ;; I think this should do something similar to CLISP's
  Luis>    ;; FFI:ALLOCATE-DEEP, and it should Just Work if we apply the :to-c
  Luis>    ;; translator, which will allocate space for "foo".

I think it depends on whether the :STRING type is an array type, a pointer
type or some magic.


  Luis>    ;; A problem here is freeing this memory. Should we tell the user
  Luis>    ;; he has to free the complex stuff inside by himself. Or should we
  Luis>    ;; come up with something similar to CLISP's FFI:FOREIGN-FREE when
  Luis>    ;; passed ":full t". (In this case CFFI:FOREIGN-FREE would have to
  Luis>    ;; take an optional type or something to describe what needs
  Luis>    ;; freeing.)

Complex stuff is complex to free, so I would say that the user has to do it.

-- 
Martin Simmons
LispWorks Ltd