[Resend] How to free the array element

[Luís Oliveira]

Hello Ying,

On Sat, Apr 11, 2015 at 1:50 AM, Huang, Ying <huang_ying_caritas at 163.com> wrote:
> I need to manipulate foreign array. I tried to define an extended
> foreign array type because there are some features that are lacking in
> foreign-array-type of cffi. I can access/assign element of foreign array
> with cffi:mem-ref and (setf cffi:mem-ref). But I don't know how to free
> element of foreign array (the element type can be aggregated).

Indeed, in src/types.lisp:455 there's a FIXME mentioning just that!


> I think if there is a cffi:mem-free (I know, the name is bad) like
> cffi:mem-ref, may be this can be resolved.
>
> (defun mem-free (ptr type param &optional (offset 0))
>   (let* ((parsed-type (parse-type type))
>          (ctype (canonicalize parsed-type)))
>     (if (aggregatep parsed-type)
>         (free-translated-object (inc-pointer ptr offset)
>                                 parsed-type param)
>         (free-translated-object (%mem-ref ptr ctype offset)
>                                 parsed-type param))))

My first intuition would be to fix foreign-array-free to get a type
argument. That way it would know how to free each element, essentially
doing a mem-free (as you call it) for each element in the array.

I've prototyped such a smarter foreign-array-free here:
https://github.com/luismbo/cffi/commit/0a7d42720eacc32abb4338df32b4e5fceecdeb6d

Your example then becomes:

CFFI> (defparameter *string-array* (foreign-array-alloc #("a" "b" "c")
'(:array :string 3)))
*STRING-ARRAY*
CFFI> (trace foreign-string-free)
(FOREIGN-STRING-FREE)
CFFI> (foreign-array-free *STRING-ARRAY* '(:array :string 3))
  0: (FOREIGN-STRING-FREE #.(SB-SYS:INT-SAP #X002054A0))
  0: FOREIGN-STRING-FREE returned NIL
  0: (FOREIGN-STRING-FREE #.(SB-SYS:INT-SAP #X002054B0))
  0: FOREIGN-STRING-FREE returned NIL
  0: (FOREIGN-STRING-FREE #.(SB-SYS:INT-SAP #X002054C0))
  0: FOREIGN-STRING-FREE returned NIL
NIL

Let me know what you think. :)

Cheers,

-- 
Luís Oliveira
http://kerno.org/~luis/