Re: sorting in C

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrew Cohen <acohen@ust.hk>
> Date: Sun, 27 Feb 2022 17:11:53 +0800
> 
>     EZ> However, from your description, it doesn't sound like the more
>     EZ> optimal approach of allocating dynamically is much more
>     EZ> complicated.  In particular, what Mattias said should be easy
>     EZ> using the unwind-protect machinery we already have (and use in
>     EZ> many similar situations).  See the calls to
>     EZ> record_unwind_protect_ptr whose first argument is 'xfree'.  We
>     EZ> also have reallocation routines ready to be used.
> 
> That is how I am handling it now, but I'm not sure if I have it right
> (sorry for the naive question):
> 
> When I need new memory I call
> 
> :   specpdl_ref sa_count = SPECPDL_INDEX ();
> :   a = (Lisp_Object *) record_xmalloc (need * sizeof (Lisp_Object));
> 
> and I save =sa_count=; I guess =record_xmalloc= handles freeing the
> memory on exception. Later during the sorting process I free the memory
> explicitly with 
> 
> : safe_free (sa_count)
> 
> Does this seem right? (Probably, since I've been running this way for
> awhile and would have expected lots of problems if I weren't allocating
> and freeing the memory :))

I'd rather you didn't use safe_free, since that is for SAFE_ALLOCA
etc.  Just use unbind_to directly, like we do elsewhere where
record_xmalloc is used.