Re: Latent bugs?

[Marko Rauhamaa <marko@pacujo.net>]

Lynn Winebarger <owinebar@free-expression.org>:

> On Saturday 28 December 2002 03:49, Marko Rauhamaa wrote:
> > 
> >   return scm_list_2(scm_cons(scm_long2num(old_timer.it_interval.tv_sec),
> >                              scm_long2num(old_timer.it_interval.tv_usec)),
> >                     scm_cons(scm_long2num(old_timer.it_value.tv_sec),
> >                              scm_long2num(old_timer.it_value.tv_usec)));
> > 
> > If I understand it correctly, this statement contains several
> > allocations, each of which can potentially trigger garbage collection
> > and delete any of the intermediate results.
>
>      The code above, though it is not explicit, will store the
> intermediate return values (references) on the stack, where the
> garbage collector will see them (and thus not free the newly created
> object). It's just how the traditional model of a C machine works.

I took a glance at gc_os_dep.c and I was surprised. It appears the GC
actually sweeps through all data segments, the stack segment and CPU
registers and heuristically locates pointers into the heap. I've used
that technique myself before, but I wouldn't have thought that was an
effective way of implementing a Lisp machine.

The Guile manual doesn't state that basically all writable memory of a
process participates in GC:

  http://www.gnu.org/software/guile/docs/guile-ref/Memory-Management.html#Memory%20Management


Marko

-- 
Marko Rauhamaa      mailto:marko@pacujo.net     http://pacujo.net/marko/


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