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|
{- daemon support
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Utility.Daemon where
import Common
import System.Posix
{- Run an action as a daemon, with all output sent to a file descriptor.
-
- Can write its pid to a file, to guard against multiple instances
- running and allow easy termination.
-
- When successful, does not return. -}
daemonize :: Fd -> Maybe FilePath -> Bool -> IO () -> IO ()
daemonize logfd pidfile changedirectory a = do
_ <- forkProcess child1
out
where
child1 = do
_ <- createSession
_ <- forkProcess child2
out
child2 = do
maybe noop (lockPidFile True alreadyrunning) pidfile
when changedirectory $
setCurrentDirectory "/"
nullfd <- openFd "/dev/null" ReadOnly Nothing defaultFileFlags
_ <- redir nullfd stdInput
mapM_ (redir logfd) [stdOutput, stdError]
closeFd logfd
a
out
redir newh h = do
closeFd h
dupTo newh h
alreadyrunning = error "Daemon is already running."
out = exitImmediately ExitSuccess
lockPidFile :: Bool -> IO () -> FilePath -> IO ()
lockPidFile write onfailure file = do
fd <- openFd file ReadWrite (Just stdFileMode)
defaultFileFlags { trunc = write }
locked <- catchMaybeIO $ setLock fd (locktype, AbsoluteSeek, 0, 0)
case locked of
Nothing -> onfailure
_ -> when write $ void $
fdWrite fd =<< show <$> getProcessID
where
locktype
| write = WriteLock
| otherwise = ReadLock
{- Stops the daemon.
-
- The pid file is used to get the daemon's pid.
-
- To guard against a stale pid, try to take a nonblocking shared lock
- of the pid file. If this *fails*, the daemon must be running,
- and have the exclusive lock, so the pid file is trustworthy.
-}
stopDaemon :: FilePath -> IO ()
stopDaemon pidfile = lockPidFile False go pidfile
where
go = do
pid <- readish <$> readFile pidfile
maybe noop (signalProcess sigTERM) pid
|
