Re: malloc & free functions

[Howard Chu <hyc@symas.com>]

Hallvard B Furuseth wrote:
> I'm getting lost in all the malloc and free functions...
> When is one supposed to use which function?  When does it matter?
>
>   ber_memalloc(), ber_memfree(),
>   LBER_FREE(), LBER_MALLOC() -defined as the two above,
>   ber_memalloc_x(), ber_memfree_x() - as as above but with ctx parameter,
>   LDAP_FREE(), LDAP_MALLOC() plus _X variants,
>   ch_malloc, ch_free() - also as above,
>   slap_sl_malloc(), slap_sl_free() - separate slapd allocator.
>
> E.g. liblber/decode.c often uses ber_memalloc_x(,ber->ber_memctx) to
> allocate but then frees that memory with LBER_FREE() which does not
> use a ctx.  Should the free use ber->ber_memctx again?  Or not, since
> ber_set_option(,LBER_OPT_BER_MEMCTX,) can change a ber_memctx and
> slapd uses it sometimes?
>
>   
Yes, I've wished for a cleaner implementation. If liblber is using the 
memctx to allocate, it ought to also use it to free. Typically slapd is 
the only thing that ever sets the memctx.

In slapd, since it was impossible to keep the two types of memory 
straight, ch_free() and slap_sl_free() will try to detect if they 
actually own the memory, and call the other free routine if not. So the 
only consequence of calling the wrong free() function is an extra 
function call overhead.

In liblber, there's no such protection, so calling the wrong free will 
probably SEGV. Looks like decode.c needs to be fixed.

It would have probably been better if the sl_malloc routines were in 
liblber, but it also has some dependencies on the thread pool functions, 
so that wasn't possible.




--
 -- Howard Chu
 Chief Architect, Symas Corp.  http://www.symas.com
 Director, Highland Sun        http://highlandsun.com/hyc
 OpenLDAP Core Team            http://www.openldap.org/project/