git annex watch --stop

Command/Watch.hs

@@ -50,27 +50,36 @@ data Change = Change
 	deriving (Show)
 
 def :: [Command]
-def = [withOptions [foregroundOption] $ 
+def = [withOptions [foregroundOption, stopOption] $ 
 	command "watch" paramPaths seek "watch for changes"]
 
 seek :: [CommandSeek]
-seek = [withFlag foregroundOption $ withNothing . start]
+seek = [withFlag stopOption $ \stopdaemon -> 
+	withFlag foregroundOption $ \foreground ->
+	withNothing $ start foreground stopdaemon]
 
 foregroundOption :: Option
 foregroundOption = Option.flag [] "foreground" "do not daemonize"
 
-start :: Bool -> CommandStart
-start foreground = notBareRepo $ withStateMVar $ \st -> do
-	if foreground
-		then do
-			showStart "watch" "."
-			liftIO $ watch st
-		else do
-			logfd <- liftIO . openLog =<< fromRepo gitAnnexLogFile
-			pidfile <- fromRepo gitAnnexPidFile
-			liftIO $ daemonize logfd (Just pidfile) False $ watch st
+stopOption :: Option
+stopOption = Option.flag [] "stop" "stop daemon"
+
+start :: Bool -> Bool -> CommandStart
+start foreground stopdaemon = notBareRepo $ do
+	if stopdaemon
+		then liftIO . stopDaemon =<< fromRepo gitAnnexPidFile
+		else withStateMVar $ startDaemon (not foreground)
 	stop
 
+startDaemon :: Bool -> MVar Annex.AnnexState -> Annex ()
+startDaemon False st = do
+	showStart "watch" "."
+	liftIO $ watch st
+startDaemon True st = do
+	logfd <- liftIO . openLog =<< fromRepo gitAnnexLogFile
+	pidfile <- fromRepo gitAnnexPidFile
+	liftIO $ daemonize logfd (Just pidfile) False $ watch st
+
 watch :: MVar Annex.AnnexState -> IO ()
 #if defined linux_HOST_OS
 watch st = withINotify $ \i -> do

Utility/Daemon.hs

@@ -27,7 +27,7 @@ daemonize logfd pidfile changedirectory a = do
 			_ <- forkProcess child2
 			out
 		child2 = do
-			maybe noop lockPidFile pidfile
+			maybe noop (lockPidFile True alreadyrunning) pidfile 
 			when changedirectory $
 				setCurrentDirectory "/"
 			nullfd <- openFd "/dev/null" ReadOnly Nothing defaultFileFlags
@@ -39,12 +39,31 @@ daemonize logfd pidfile changedirectory a = do
 		redir newh h = do
 			closeFd h
 			dupTo newh h
+		alreadyrunning = error "Daemon is already running."
 		out = exitImmediately ExitSuccess
 
-lockPidFile :: FilePath -> IO ()
-lockPidFile file = void $ do
+lockPidFile :: Bool -> IO () -> FilePath -> IO ()
+lockPidFile write onfailure file = do
 	fd <- openFd file ReadWrite (Just stdFileMode) defaultFileFlags
-	catchIO
-		(setLock fd (WriteLock, AbsoluteSeek, 0, 0))
-		(const $ error "Daemon is already running.")
-	fdWrite fd =<< show <$> getProcessID
+	when (write) $ void $
+		fdWrite fd =<< show <$> getProcessID
+	catchIO (setLock fd (locktype, AbsoluteSeek, 0, 0)) (const onfailure)
+	where
+		locktype
+			| write = WriteLock
+			| otherwise = ReadLock
+
+{- Stops the daemon.
+ -
+ - The pid file is used to get the daemon's pid.
+ -
+ - To guard against a stale pid, try to take a nonblocking shared lock
+ - of the pid file. If this *fails*, the daemon must be running,
+ - and have the exclusive lock, so the pid file is trustworthy.
+ -}
+stopDaemon :: FilePath -> IO ()
+stopDaemon pidfile = lockPidFile False go pidfile
+	where
+		go = do
+			pid <- readish <$> readFile pidfile
+			maybe noop (signalProcess sigTERM) pid

doc/git-annex.mdwn

@@ -177,7 +177,8 @@ subdirectories).
   background, you no longer need to manually run git commands when
   manipulating your files.
 
-  To not daemonize, run with --foreground
+  To not daemonize, run with --foreground ; to stop a running daemon,
+  run with --stop
 
 # REPOSITORY SETUP COMMANDS