>>>>> "Tom" == Tom Lord <xxxxxx@emf.net> writes:

Tom> If the root set is large, certainly it should be traced in several
Tom> steps, using barriers to preserve its invariants.

Is there a practical example of a system that does this?  It seems
very difficult to do, even absent an FFI to C, as your typical root
set---the current continuation---changes *all the time*.  (I'm really
curious.  I could never wrap my mind around this.)

In 1997, I developed the prototype for this FFI concurrently with
hooking RScheme's incremental collector into Scheme 48, so there's
some evidence that the FFI works with incremental collection in
principle.

Tom> Absent any further guidance from the FFI spec, I would expect some
Tom> programs to register a very large number of locations -- and worse,
Tom> locations scattered widely in memory -- using
Tom> SCHEME_GC_PROTECT_GLOBAL.  (Why wouldn't I, in a printed circuit board
Tom> CAD program, GCPROtect a field of every C structure representing an
Tom> edge in a netlist graph?)

Because of what you just said? :-)

--
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla