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[Caml-list] camlidl and pointer to function
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Date: 2001-11-14 (12:15)
From: Dmitry Bely <dbely@m...>
Subject: Re: [Caml-list] camlidl and pointer to function
"NASSOR Eric" <> writes:

> > I have a C library function with interface like following:
> >
> > typedef [abstract] void* SomeType;
> > typedef int (*CallBack)(int);
> > void convert( SomeType* in, SomeType* out, CallBack c);
> >
> > It would be nice to use it in caml the following way:
> >
> > external convert: someType->someType->(int->int)->unit = "something"
> > ...
> > convert stIn stOut ((+) 1)
> > ...
> >
> > Unfortinately CamIDL language does not allow the pointer to function as a
> > valid type, but maybe there is some common solution/workaround for this
> > problem? Or the only way is writing necessary stubs and conversion
> > functions by hands? Is is possible at all?
> >
> It is possible to call back caml code from a C code which was called from caml, but
> you need to write a few lines of code.
> here is an example extracted from my application (with a few simplifications).
> the resulting caml function iter_tree can be called recursively, it can also raise
> exceptions.

The problem is that C library is binary-only (Intel image processing
library), and CallBack type is exactly 

typedef int (*CallBack)(int);

I cannot add value parameter containing Caml callback here. I can store it
in a global C variable, but then the entire application will be not
thread-safe. Locking the entire ml2c(); f(); c2ml(); section is also not

Hope to hear from you soon,

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