Date: Mon, 5 Jan 2004 08:51:41 -0800 (PST)
   From: Tom Lord <xxxxxx@emf.net>

   In short, the FFI requires a root set of unbounded size and
   unrestricted locality:

Yes, just like Scheme's CONS requires a heap of unbounded
size.  No FFI is going to make all programs using it run in
all implementations.

   The problem goes away if the FFI imposes barriers over GCPROtected
   values.

It wouldn't take much of a change to do this.  A macro like
   SCHEME_SET_GLOBAL(location, value)
would do it.  A similar macro would work to support a read
barrier, but I believe that those are significantly less common.

                                      -Richard Kelsey