95 lines
2.7 KiB
Haskell
95 lines
2.7 KiB
Haskell
{- daemon support
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-
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- Copyright 2012 Joey Hess <joey@kitenet.net>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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module Utility.Daemon where
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import Common
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import System.Posix
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{- Run an action as a daemon, with all output sent to a file descriptor.
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-
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- Can write its pid to a file, to guard against multiple instances
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- running and allow easy termination.
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-
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- When successful, does not return. -}
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daemonize :: Fd -> Maybe FilePath -> Bool -> IO () -> IO ()
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daemonize logfd pidfile changedirectory a = do
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_ <- forkProcess child1
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out
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where
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child1 = do
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_ <- createSession
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_ <- forkProcess child2
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out
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child2 = do
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maybe noop lockPidFile pidfile
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when changedirectory $
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setCurrentDirectory "/"
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nullfd <- openFd "/dev/null" ReadOnly Nothing defaultFileFlags
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_ <- redir nullfd stdInput
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mapM_ (redir logfd) [stdOutput, stdError]
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closeFd logfd
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a
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out
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redir newh h = do
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closeFd h
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dupTo newh h
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out = exitImmediately ExitSuccess
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{- Locks the pid file, with an exclusive, non-blocking lock.
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- Writes the pid to the file, fully atomically.
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- Fails if the pid file is already locked by another process. -}
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lockPidFile :: FilePath -> IO ()
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lockPidFile file = do
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createDirectoryIfMissing True (parentDir file)
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fd <- openFd file ReadWrite (Just stdFileMode) defaultFileFlags
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locked <- catchMaybeIO $ setLock fd (WriteLock, AbsoluteSeek, 0, 0)
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fd' <- openFd newfile ReadWrite (Just stdFileMode) defaultFileFlags
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{ trunc = True }
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locked' <- catchMaybeIO $ setLock fd' (WriteLock, AbsoluteSeek, 0, 0)
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case (locked, locked') of
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(Nothing, _) -> alreadyrunning
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(_, Nothing) -> alreadyrunning
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_ -> do
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_ <- fdWrite fd' =<< show <$> getProcessID
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renameFile newfile file
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closeFd fd
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where
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newfile = file ++ ".new"
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alreadyrunning = error "Daemon is already running."
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{- Checks if the daemon is running, by checking that the pid file
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- is locked by the same process that is listed in the pid file.
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-
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- If it's running, returns its pid. -}
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checkDaemon :: FilePath -> IO (Maybe ProcessID)
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checkDaemon pidfile = do
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v <- catchMaybeIO $
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openFd pidfile ReadOnly (Just stdFileMode) defaultFileFlags
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case v of
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Just fd -> do
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locked <- getLock fd (ReadLock, AbsoluteSeek, 0, 0)
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p <- readish <$> readFile pidfile
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return $ check locked p
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Nothing -> return Nothing
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where
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check Nothing _ = Nothing
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check _ Nothing = Nothing
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check (Just (pid, _)) (Just pid')
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| pid == pid' = Just pid
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| otherwise = error $
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"stale pid in " ++ pidfile ++
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" (got " ++ show pid' ++
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"; expected " ++ show pid ++ " )"
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{- Stops the daemon, safely. -}
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stopDaemon :: FilePath -> IO ()
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stopDaemon pidfile = go =<< checkDaemon pidfile
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where
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go Nothing = noop
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go (Just pid) = signalProcess sigTERM pid
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