From: Jim Blandy <xxxxxx@redhat.com>
   Date: 07 Jan 2004 17:01:17 -0500

   I gather that your current inclination is to preserve the requirement
   that GC may only take place during calls to specially marked API
   functions.  Thus, collection must wait until all active C calls have
   called a marked API function.  Is that correct?

Yes.  An exception, which should be mentioned in the SRFI and
may affect your situation, is that systems using a conservative
GC could GC at any time.

   However, I would like to be able to use Scheme as an extension
   language for existing C programs that use multiple system threads, and
   I would like SRFI-50 to provide what I need to implement the C/Scheme
   glue for this.

To be useful in such a situation there would need to be a way to exit
and then re-enter the implicit critical section surrounding C calls.

                                          -Richard Kelsey