[cffi-devel] calling a function of the same name from two DLLs

[Gregory Martin Pfeil]

On 17 Dec 2006, at 21:15, Jack Unrue wrote:

> Is there any caching of CFFI foreign function meta-data behind the  
> scenes,
> perhaps keyed by the foreign function name? Such as might be causing
> identical results no matter which is called first, or which load- 
> foreign-library
> occurs first?
>
> Note: my WinXP install has several different versions of  
> comctl32.dll, one of
> which matches the shell32.dll version, but I have at least one  
> configuration
> where I know the result really is wrong (as if the result from the  
> other
> DllGetVersion call was being cached).

The issue here is that CFFI doesn't have any way to tell which of the  
DllGetVersion functions you want to call. Both DEFCFUNs are pointing  
at the same name. This is one of the things that UFFI still handles  
better (unless I just haven't been keeping up-to-date with CFFI).

In UFFI, rather than

>    (load-foreign-library "comctl32.dll")

You would say:

	(load-foreign-library "comctl32.dll" :module "comctl")
	(load-foreign-library "shell32.dll" :module "shell")

then, when defining the functions:

	(def-function ("DllGetVersion" comctl-dll-get-version)  
((info :pointer))
	              :returning HRESULT
	              :module "comctl")

	(def-function ("DllGetVersion" shell-dll-get-version) ((info :pointer))
	              :returning HRESULT
	              :module "shell")

you can see the extra ":module" parameter, which tells it which DLL  
contains the function you want to use. I'm pretty sure it's not  
possible to do anything similar from CFFI.

I thought this was being worked on, but I haven't been paying  
attention too much lately.