Re: [Chicken-users] "Dynamically Loading" non-entry-point code

[Felix Winkelmann]

Daniel B. Faken wrote:

> On Tue, 22 Jun 2004, felix wrote:
>
> > Daniel B. Faken wrote:
> >
> > > I need to call it from C (because I want the library to basically load 
> > > some of its own bindings), so I defined this in my "scmif" interface
> > > layer (see below)
> > >
> > > Do you see any problem with this?  (I wasn't too sure what you meant by 
> > > "it gets complicated")   Will this work with arbitrarily nested layers of 
> > > callback?
>
> <snip>
>
> > This could actually work, but I'm not totally sure.
> > Does it crash? ;-)
> >
> > cheers,
> > felix
>
>
>   Sorry, I should have mentioned that; it *seems* to work just peachy.  I 
> have happily been able to simplify three separate packages this way.  My 
> question was more regarding if there was some theoretical problem..
> I.e. what exactly would calling it 'just' from scheme (as per your 
> suggestion) do differently from my C-calling-Scheme + one-layer-of-indirection
> code?

By what I can infer from your example, it should work. The important
issue is to make sure no calls from Scheme to C into Scheme happen, that might
trigger a garbage collection without saving some context data (like the
continuation of the outermost Scheme context).
The other important issue is that, for GC to work, a "restart" trampoline
has to be established, so that once a minor GC has been run, something
is there that can be longjmp'd to.
And yet another important issue is that a minor GC may not simply remove
live C stack frames.

Depending on your definition of scmif_eval_stringf, your example looks ok to me.

>   FWIW, I've also used this kind of indirection technique to add scheme
> bindings to C functions at run-time and to add a safety layer so functions 
> can be called whether the Chicken toplevel is active or not 

Interesting. Can you give more information about how you setup the
safety layer?

> (thanks for 
> adding CHICKEN_is_running() :) ).

You're welcome. Happy customers is our goal.


cheers,
felix