Sven Panne wrote:
Am Samstag, 25. März 2006 20:00 schrieb Brian Hulley:
I've found a workaround to the problem below: instead of trying to use hs_free_fun_ptr, I instead pass a FunPtr to the Haskell function freeHaskellFunPtr into my DLL, and use this to free everything, finally using it to free itself (!) which I assume should be safe. [...]
It has been quite some time since I've worked on GHC's Adjustor.c and Hugs' FFI, but IIRC it is in general *not* safe to do this. On some platforms code is being generated dynamically for these kind of callbacks, which has already been freed by the time the callback returns. This might appear to work, depending on your processor architecture and dynamic memory management behaviour, but it's better not to rely on this. Perhaps the FFI spec should be clearer here.
I'm pretty sure this *does* work with GHC, at least on some platforms (definitely x86 and x86_64, I'm not sure about the others). We're careful not to require any dynamically-allocated code to run when the callback returns. I agree the FFI spec should be clearer here. Cheers, Simon