Re: [Haskell-cafe] How to daemonize a threaded Haskell program?

On 5 March 2011 21:43, Donn Cave wrote:

Quoth Bas van Dijk , ...

...

I understand why it's problematic to fork a process which is in the middle of running multiple simultaneous threads. However, in the case of a daemon the fork happens in the beginning of the program. So if I can manage to create a program that first daemonizes my process then starts the Haskell program, all is good.

type ProcessID = CInt type Fd = CInt

foreign import ccall "fork" c_fork :: IO CInt foreign import ccall "_exit" _exit :: CInt -> IO ()

fork :: IO Int -> IO ProcessID fork fn = do        pid <- c_fork        if pid == 0                then do                        fn >>= _exit . fromIntegral                        return 0 -- unused, I reckon                else if pid > 0                        then return pid                        else throwErrno "fork"

System.PosixProcess (exitImmediately) is supposed to be "_exit".

I would not care to hazard a guess as to whether this will work reliably for you.

Thanks, I thought about this too, however I consider myself too unfamiliar with the RTS to know if this is safe. Bas