Problem exporting Haskell to C via a DLL in GHC 6.6

[Brian Hulley]

Simon Peyton-Jones wrote:
> I don't think there is any reason in principle why GHC can't generate
> DLLs that "just work", but plainly it's deficient at the moment.

The fundamental reason is that the DLL mechanism itself doesn't allow 
initialization/ shutdown do be hidden from the user of a DLL, because the 
order of loading/unloading DLLs is unspecified by the MS Windows operating 
system. Therefore it's not a GHC problem - it's just a fact of life with 
DLLs...

> The other thing is that we could do with more "how to" documentation
> about GHC and DLLs.  We have a bit here:
>         http://haskell.org/haskellwiki/GHC/Using_the_FFI
> Could you expand it in the light of your experience?

I've added a section 
http://haskell.org/haskellwiki/GHC/Using_the_FFI#Beware_of_DllMain.28.29.21 
which attempts to explain why init/exit code can't be put in DllMain, as 
well as an *untested* example to show what I meant by putting init/exit code 
in Begin/End functions instead.

I've put a note next to the example to say that it's untested, and to appeal 
to anyone with more knowledge of static linking between Haskell and C to fix 
anything I've missed or replace with a better example. (Apologies for not 
testing it but static linking to stubs generated by GHC seems to require the 
DLL to be compiled by gcc and use of gcc on Windows seems to require Cygwin 
since gcc doesn't seem to understand Windows paths and I don't have Cygwin 
installed - unfortunately at the moment I don't have time to pursue this 
further.)

Best regards, Brian.
-- 
http://www.metamilk.com