I hope this question isn't too stupid, but I can't find any obvious way to do this from reading the ghc docs.
What I want to do is call a final foreign function (a library shutdown routine) when Haskell terminates, but after all ForeignPtr finalisers have been run.
I suppose I could implement some kind of finaliser counter so the last finalizer could tell it was the last finaliser and call the shutdown routine, but this seems a little awkward, especially as these days the FFI requires finalisers to be foreign functions.
The other possibility that occurs to me is that I call performGC at the very end of the program, immediately before calling the library shutdown routine. But I'm not too sure whether that will guarantee that all finalizers have been run even if there are no live references to foreign objects at that point. (Using GC as described in the "non-stop Haskell" paper it seems possible that finalisers won't be run immediately in response to performGC.)
Using an explicit reference count sounds fine to me. The runtime system doesn't support any ordering constraints between finalizers (it's a really hard problem in general), so the party line is "you have to code it up yourself". Actually, I seem to recall that we were going to disable the running of finalizers at the end of the program completely, in which case you would have to add your cleanup code in the main thread, with an appropriate exception handler. Cheers, Simon