Re: [mituharu@math.s.chiba-u.ac.jp: Re: emacs-22.1 with GTK dumps core when Gnome wigets clicked]

[Ken Raeburn <raeburn@raeburn.org>]

On Jun 25, 2007, at 04:30, YAMAMOTO Mitsuharu wrote:
>> Nor is this change guaranteed to cause there to be only one access to
>> "__malloc_hook", unless you change it to be declared volatile.  (And,
>> in fact, if you're optimizing, I would've expected it to be only one
>> access in the original code on nearly all platforms.)
>
> As a matter of fact, the original code caused a real problem:
>
>   http://lists.gnu.org/archive/html/bug-gnu-emacs/2007-06/ 
> msg00170.html

I'd believe it could be, sure.  But if that code were produced with  
gcc -O2, I'd be disappointed.  Other compilers ... eh, some of them  
aren't that good. :-)

>> Mutex protection around accesses to the hook variable would be the
>> safest (and wouldn't require temporary variables or volatile
>> qualifiers), though performance would not be as good.
>
> Temporary variables will be necessary so that we can unlock the mutex
> before the actual call to the hook.  We also need to add some special
> functions to change the hook variables and use them instead of
> assignments to the hook variables in alloc.c.  That's why I said that
> "malloc in glibc 2.5 also does the same thing and I suspect that we
> cannot do better as long as we try to keep the same interface with
> respect to __malloc_hook etc." in
> http://lists.gnu.org/archive/html/emacs-devel/2007-06/msg01503.html

Yes, I think keeping the current glibc interface -- at least, as the  
one we actually use -- seems like a poor idea.  Though the change  
should be coordinated with glibc maintainers, of course.

Ken