Re: Introspection API

[Owen Taylor <otaylor redhat com>]

On Fri, 2005-02-25 at 11:08 -0500, John Ehresman wrote:
> Matthias Clasen wrote:
> > Is using libffi or something similar a problem ? 
> 
> I think we want to set things up so libffi could be easily used.  In 
> other words, the information that libffi needs should be easily 
> obtainable from the introspection api.  I'd also like not to have to 
> wrap everything in GValue's if that can be avoided.  That said, we need 
> to figure out how to package libffi for non-gcc compilers such as MS VC++.

libffi in my memory has a pretty horrid interface, and I think there
is some value in wrapping in something more GLibish. 

GValue has significant performance problems, but perhaps we could just
reuse it as a union and forget g_value_set_object() and friends for this
usage. On the other hand, that might be confusing, so maybe a separate
union structure (without the excessive space consumption of GValue)
would make sense. 

A wrapper also gives the ability to use something else internally -
perhaps the XptCall stuff from Mozilla which certainly works with
MSVC. (I haven't really looked at the portability of libffi. The
libgcj version is mixed up with GCC extensions, but that may not
be fundamental to its operations.)

My basic idea is that we'd provide something like:

 g_function_desc_invoke (GFunctionDesc    *desc, 
                         const GArgument  *in_args,
                         int               n_in_args,
                         const GArgument  *out_args,
                         int               n_out_args,
                         GArgument        *return_value);

Where GFunctionDesc is the API object for FunctionBlob. (I forget
what it was called in Matthias's writeup.) You'd also want the reverse
marshaling from C to GArgument.

Regards,
						Owen