Re: scm_mark_dependencies & guardians

[Han-Wen Nienhuys]

address@hidden writes:
> I don't want to comment on the big picture, just one note: it is
> important that marking is done in a 'tail calling' way.  That is, we
> must not recurse when marking the spine of a list, for example.  That
> is the reason for the goto in gc_mark.

Sure, otherwise you get stack overflow.

> Hmm, I don't think we should fear goto.  Sometimes it is clearer to
> use goto than it is to avoid it.  The main spaghetti in gc.c is the
> inclusion in itself.  What about moving the marking code into a
> separate file and including it twice?  We already do this for
> num2float and num2integral.

I already recoded it without inclusion. You can get around including a
file twice by doing

        mark (SCM p)
        {
           if (marked(p)) return;
           set_mark(p);
           mark_dependencies (p);
        }

        mark_dependencies(SCM p)
        {
        again:
                switch (tag(p))
                {

                   .... // lots of cases jumping to mark_next

                }
                
                return;

        mark_next:

           if (marked(p)) return;
           set_mark(p);
           goto again;

        }


-- 

Han-Wen Nienhuys   |   address@hidden    | http://www.cs.uu.nl/~hanwen/