1) Finalizers are not (some say cannot) be guaranteed to run, even on normal program termination, even if you force GC before exiting.
I only need a guarantee that it will be run if the Ptr is no longer being referenced.
This is exactly the guarantee you _don't_ have. The only guarantee you have is that it _won't_ be run if the Ptr _is_ being referenced.
I would suggest you find some way to accomplish what you want without using finalizers.
That would require the user to manually free up resources once they're not needed anymore. Something which I believe is a bit too low-level for my tastes. I basically want the user to be able to just create a sound resource and then play it, without having to do any book-keeping as to when the sound resource is not used anymore and can be released.
My concern is that this approach is a little too non-deterministic. Because playing sound involves HW resources, it is better to make users do the bookkeeping and have well-defined behavior rwt releasing resources. That said, you can probably get what you want by using weak pointers. Wrap up your Ptr in a ForiegnPtr and wrap _that_ up in an abstract datatype, and attach a weak pointer to the ForeignPtr (make sure all functions that access the Ptr use 'withForeignPtr' or 'touchForeignPtr'). Add a (Ptr,WeakPtr ()) pair to a list of "open" songs, which is monitored by a single clean-up thread (use an MVar for the list). Return the high level value to the user; when the enclosed ForeignPtr is garbage collected deRefWeak on the weak pointer will return Nothing. Then the clean-up thread can begin polling the song object to see if it is finished. You can also poke this thread at program-end to force it to free all resources it knows about, so that your program behaves well, assuming normal termination. Weak pointers are documented here: http://www.haskell.org/ghc/docs/latest/html/libraries/base/System.Mem.Weak.h... I think that something like this would work: module MySongs ( Song, mkSong, something ) where foreign .... makeASong :: whatever -> IO (Ptr ()) foreign .... doSomething :: Ptr () -> IO () data Song = Song ForeignPtr mkSong :: whatever -> MVar [(Ptr,Weak ())] -> IO Song mkSong x mvar = do p <- makeASong x f <- newForeignPtr_ p w <- mkWeak f () l <- takeMVar mvar putMVar mvar ((p,w):l) return Song f something :: Song -> IO () something (Song f) = do withForeignPtr f \p -> do doSomething p