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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 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
{- Locks the pid file, with an exclusive, non-blocking lock.
- Runs an action on failure. On success, writes the pid to the file,
- fully atomically. -}
lockPidFile :: IO () -> FilePath -> IO ()
lockPidFile onfailure file = do
fd <- openFd file ReadWrite (Just stdFileMode) defaultFileFlags
locked <- catchMaybeIO $ setLock fd (WriteLock, AbsoluteSeek, 0, 0)
fd' <- openFd newfile ReadWrite (Just stdFileMode) defaultFileFlags
{ trunc = True }
locked' <- catchMaybeIO $ setLock fd' (WriteLock, AbsoluteSeek, 0, 0)
case (locked, locked') of
(Nothing, _) -> onfailure
(_, Nothing) -> onfailure
_ -> do
_ <- fdWrite fd' =<< show <$> getProcessID
renameFile newfile file
closeFd fd
where
newfile = file ++ ".new"
{- Checks if the daemon is running, by checking that the pid file
- is locked by the same process that is listed in the pid file.
-
- If it's running, returns its pid. -}
checkDaemon :: FilePath -> IO (Maybe ProcessID)
checkDaemon pidfile = do
v <- catchMaybeIO $
openFd pidfile ReadOnly (Just stdFileMode) defaultFileFlags
case v of
Just fd -> do
locked <- getLock fd (ReadLock, AbsoluteSeek, 0, 0)
p <- readish <$> readFile pidfile
return $ check locked p
Nothing -> return Nothing
where
check Nothing _ = Nothing
check _ Nothing = Nothing
check (Just (pid, _)) (Just pid')
| pid == pid' = Just pid
| otherwise = error $
"stale pid in " ++ pidfile ++
" (got " ++ show pid' ++
"; expected" ++ show pid ++ " )"
{- Stops the daemon, safely. -}
stopDaemon :: FilePath -> IO ()
stopDaemon pidfile = go =<< checkDaemon pidfile
where
go Nothing = noop
go (Just pid) = signalProcess sigTERM pid
|
