Re: [Sbcl-help] Is it safe to use alien-lambda with closures?

[Nikodemus S. <nik...@ra...>]

On 9/18/07, Bruno Daniel <bru...@gm...> wrote:

> I thought it over and now I understand why this function is undocumented:
> Using closures as callbacks will result in a serious memory leak: Since the
> C code might have stored the function pointer anywhere, Lisp will never be
> able to garbage collect the closure.

Quite so. Constructing the callback for a closure is also
horrendously expensive compared to non-closures:

(defun foo (x)
  (alien-lambda () ... x ...))

(defun bar ()
  (alien-lambda () ...))

FOO needs to round-trip through the compiler every time, whereas
BAR does that only on the first call.

...but the reason for this being undocumented is just a feature
of me having run out of steam & time while working on this.

> I must find another solution for my application.

Most C libraries using callbacks have a separate "data" argument
to the callback you can use.

Cheers,

 -- Nikodemus