Re: [gobo-eiffel-develop] geant file for libexml

[Andreas L. <no...@sb...>]

On Mon, 2001-10-22 at 00:24, Eric Bezault wrote:
> Andreas Leitner wrote:
> > 
> > Problem fixed. The see code was still looking for EP_EVENT_PARSER,
> > whereas it has been renamed to XP_EVENT_PARSER. I have also now
> > added code that checks if the class we resolve is actually in the
> > system. An exception is raised otherwise. This code is protected
> > via an #ifdef and can be enabled by setting ${GOBO_C_DEBUG} before
> > executing geant compile in library/xml/impl/expat/spec/c.
> 
> I had a chance to have a look at the C code in 
> library/xml/impl/expat/spec/c when I tried to 
> make it work with MSVC++ 6.0 this week, and
> personally I don't think that it is a good way
> of programming to access the Eiffel routines
> from C by name using Cecil. It is no safe (see
> the exception raisings that you added), it is
> error-prone (see the segfault you got just 
> because you renamed a class), and it is not
> efficient (class names and feature names are
> probably searched for in hash tables each time
> the corresponding Eiffel routine is to be
> called, even if the routine won't change between
> two calls.
> 
> A much better solution is to pass the function
> pointers of the Eiffel routines from the Eiffel
> side to the C side in an initialization routine,
> and then the C code has these functions pointers
> in global variables once and for all, and there
> is no need for Cecil to get them by name anymore.

This makes sense. IIRC that dynamic stuff came from Berend. Berend was
there any other reason not to use function pointers?

> Example:
> 
> In Eiffel code:
> 
>   f is
>      do
>         ...
>      end
> 
>   g is
>      do
>         ...
>      end
> 
>   initialize is
>          -- Pass function pointers of `f' and
>          -- `g' to C.
>      do
>          c_initialize ($f, $g)
>      end

Ok, we just need to make sure the globals are thread safe.

> feature {NONE} -- External
> 
>   c_initialize (fp, gp: POINTER) is
>          -- Pass function pointers of `f' and
>          -- `g' to C.
>      external
>          "C"
>      end
> 
> In C code:
> 
> EIF_PROCEDURE eif_f, eif_g;
> 
> void c_initialize (EIF_PROCEDURE fp, EIF_PROCEDURE gp)
> {
>    eif_f = fp;
>    eif_g = gp;
> }


using something like c_assume_initialize should make this thread safe
(if there is a thread issue to begin with - not sure):


void c_assure_initialize (EIF_PROCEDURE fp, EIF_PROCEDURE gp)
{
	if (eif_f != null)
		eif_f = fp;
	if (eif_g != null)
   		eif_g = gp;
}

Btw, do you know if procedures can be moved around in ISE? Maybe this
sounds like a stupid question, but I really don't know. Meaning do we
need to protect the function pointers?

Anyway, if Berend has no reason why the other approach doesn't work,
I'll convert the code.

thanks,
Andreas