On Wed, Jan 21, 2009 at 11:36 PM, Belka <lambda-belka@yandex.ru> wrote:

Hi!

Could somebody please share some experience on how to implement daemon start
and stop directives. In theory I need something like this:
1. "my_daemon start" - starts my app with an infinite loop of serving
inside.
2. "my_daemon stop" - puts in some TVar a value signalizing, that stop is
given - infinite loop brakes.

You can abstract this pattern:

-- runs its argument in an infinite loop, and returns an action that stops the loop

daemon :: IO () -> IO (IO ())

daemon action = do

stopvar <- atomically $ newTVar False

let run = do

stop <- atomically $ readTVar stopvar

if stop then return () else (action >> run)

forkIO run

return (atomically $ writeTVar stopvar True)

TVars are overkill here, actually, an IORef would be just fine, I think.

Luke