Re: Protecting C code from continuations

[Gary Houston]

> Date: Wed, 07 Jul 2004 21:26:21 +0100
> From: Neil Jerram <address@hidden>
> Cc: address@hidden
> 
> Gary Houston wrote:
> 
> > I wrote something a while ago that I think is relevant to this. In CVS:
> > 
> > guile/workbook/extension/dynamic-root.text 
> 
> Thanks Gary, that's interesting.  However, it still doesn't do what I'm 
> looking for, I'm afraid, because I actually want to be able to invoke a 
> continuation within one C->Scheme entry point that was captured during a 
> previous C->Scheme entry point.
> 
> I now think that I can achieve what I want by making all the C->Scheme 
> entry points look like this:
> 
> (define last-c-continuation #f)
> 
> (define (entry-point ...)
>    (call/cc (lambda (cont)
>               (set! last-c-continuation cont)
>               (catch #t
>                      interesting-stuff
>                      exception-handler)
>               (last-c-continuation #f))))
> 
> Then, even if `interesting-stuff' invokes a continuation, it will jump 
> into a call stack that is identical as far as the high level frames 
> shown here are concerned; and the new call stack will still invoke 
> last-c-continuation, thus restoring the stack for the containing C code.
> 
> Any comments on this, including whether it will or won't work?

It's devious, but I can't think of any reason why it wouldn't work.

Gary