Re: Outline for Guile Generational GC

[Dale Jordan <dalej@alum.mit.edu>]

The documentation on smobs indicates that a new instance is allocated
by scm_must_malloc, after which the C program must build a cell with
the correct type tag and a pointer to the malloc-ed memory.  There is
no mention whether an alternate means is allowed.  Unfortunately,
scm_must_malloc is used all over Guile itself, so we couldn't use it
directly to find smobs.  There wouldn't seem to be any restriction on
using it for other purposes, either.

We could try the value-added approach and provide a function defined as

   SCM *scm_make_instance(long smob_tag, scm_sizet smob_size)

that did the allocations and returned the cell pointer already set
up.  This would let us control where the memory was allocated from.
It would have to become the only supported way to allocate a smob
instance.

I haven't looked at many smobs, but the few I've defined have not kept
pointers to scheme objects.  It might be helpful if the smob
description provided that information.  If they don't hold pointers
they don't have to be traced except when their header cell is collected.

Dale.