Re: scm_mark_dependencies & guardians

[Han-Wen Nienhuys <hanwen@cs.uu.nl>]

mvo@zagadka.ping.de 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   |   hanwen@cs.uu.nl    | http://www.cs.uu.nl/~hanwen/


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