[Haskell-cafe] Re: libefence useful for debugging ghc+ffi programs?

[Johannes Waldmann]

> > and indeed, gethostbyname is famous for being non re-entrant.

it already has a lock in Network.BSD, so I assume it's fine:


{-# NOINLINE lock #-}
lock :: MVar ()
lock = unsafePerformIO $ newMVar ()

withLock :: IO a -> IO a
withLock act = withMVar lock (\_ -> act)

getHostByName :: HostName -> IO HostEntry
getHostByName name = withLock $ do
  withCString name $ \ name_cstr -> do
   ent <- throwNoSuchThingIfNull "getHostByName" "no such host entry"
                $ trySysCall $ c_gethostbyname name_cstr
   peek ent