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Re: Protecting C code from continuations

From: Neil Jerram
Subject: Re: Protecting C code from continuations
Date: Wed, 07 Jul 2004 21:26:21 +0100
User-agent: Mozilla/5.0 (X11; U; Linux 2.4.4-4GB i686; en-US; 0.8.1) Gecko/20010515

Gary Houston wrote:

I wrote something a while ago that I think is relevant to this. In CVS:


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
             (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?


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