Protecting C code from continuations

[Neil Jerram]

Hi all,

I'm working with some C code that is not continuation-safe; 
specifically, because it will fail in some way if the points of entry 
from C into Scheme code appear to return more than once.  However, it 
would be useful if I could use continuations to save and restore context 
as far as the Scheme stack is concerned.

Given this, is there any way of being able to use continuations within 
Scheme but protecting the C code from them?

I was wondering about using something like this at all the Scheme-from-C 
entry points ...........

(define-macro (with-continuation-barrier . body)
  `(call/cc
     (lambda (cont)
       (dynamic-wind
         noop
         (lambda () ,@body)
         (lambda () (cont #f)))))

..... but I suspect this doesn't work, because when I call a 
continuation deep within the Scheme code (i.e. the continuation that I 
really want to use, not the one used as part of the barrier here), that 
continuation would replace the current dynamic-wind context with the one 
that was in effect when the continuation was created -- which is exactly 
what I don't want.

Any comments/ideas?

Thanks,
      Neil