Well that shouldn't affect the functionality. The weak pointer was only a way of attatching a finalizer to the Playback object. It is true that I should probably wrap up the the SoundPlaybackRaw inside the SoundPlayback as well, to save CPU, but it shouldn't matter for the core functionality.
I'm not sure I understand.
If I were okay with that I'd just spawn a new one for each Playback, which would be considerably cleaner I think than having a single loop with some sort of master database of playbacks...
I think both of these are cleaner than starting a new thread at finalize time. At any rate, here is a quick hack of mine that I think does what you want, using a master clean up thread that is only awake when songs are "playing". Feel free to play with/use it at will. Note it doesn't guarantee that every song is freed. module Main where import List import Monad import Random import Foreign import GHC.ForeignPtr import System.Mem import System.Mem.Weak import Control.Concurrent import Control.Concurrent.MVar -- pretend these are foreign imports that really do things... newSong :: String -> IO (Ptr ()) newSong name = return nullPtr songDone :: Ptr () -> IO Bool songDone p = do x <- getStdRandom( randomR (1,100) ) if x >= (85::Int) then return True else return False freeSong :: Ptr () -> IO () freeSong p = return () -------------------- newtype Song = Song (ForeignPtr ()) data LibState = LibState { listMV :: MVar [Ptr ()] , waitMV :: MVar Bool , killMV :: MVar () } songFinalizer :: LibState -> Ptr () -> IO () songFinalizer libstate p = do modifyMVar_ (listMV libstate) (return . (p:)) tryPutMVar (waitMV libstate) False return () mkSong :: LibState -> String -> IO Song mkSong libstate name = do p <- newSong name f <- newConcForeignPtr p (songFinalizer libstate p) return (Song f) cleanupThread :: MVar [Ptr ()] -> MVar Bool -> MVar () -> IO () cleanupThread listMVar waitMVar killMVar = let loop l = do shouldDie <- takeMVar waitMVar putStrLn "cleanup thread awoken..." l' <- swapMVar listMVar [] when (null l' && not shouldDie) (threadDelay 1000000) notdone <- filterM (\x -> do d <- songDone x if d then putStrLn "freeing song..." >> freeSong x >> return False else return True ) (l ++ l') unless (null notdone) (tryPutMVar waitMVar False >> return ()) if shouldDie then return notdone else loop notdone in do putStrLn "starting cleanup loop" l <- loop [] putStrLn "done with cleanup loop" sequence_ (map (\x -> freeSong x >> putStrLn "freeing song late...") l) putMVar killMVar () initLib :: IO LibState initLib = do listMVar <- newMVar [] waitMVar <- newEmptyMVar killMVar <- newEmptyMVar putStrLn "starting cleanup thread" forkIO (cleanupThread listMVar waitMVar killMVar) let libstate = LibState { listMV = listMVar , waitMV = waitMVar , killMV = killMVar } return libstate shutdownLib :: LibState -> IO () shutdownLib libstate = do putMVar (waitMV libstate) True takeMVar (killMV libstate) main = do libstate <- initLib putStrLn "doing stuff" s <- mkSong libstate "my crazy song" let x = last $ takeWhile (< 10000000) $ iterate (+1) 1 putStrLn (show x) putStrLn "done with stuff" shutdownLib libstate putStrLn "bye"