On Thu, Jan 22, 2009 at 8:11 AM, Belka
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
Thanks, Luke!
Why do you write "return (atomically $ writeTVar stopvar True)" in the end?
Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe...
I think you should follow Unix "standards" in this case. So depending on what you kind of communication you are looking for you have different options (this is based on my understanding of the Unix way): * Signals - for simple control, such as getting the daemon to stop, reread its configuration, or restart * Pipe/Socket - for more complex control such as job control /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe