more lock file refactoring

Also fixes a test suite failures introduced in recent commits, where
inAnnexSafe failed in indirect mode, since it tried to open the lock file
ReadWrite. This is why the new checkLocked opens it ReadOnly.

This commit was sponsored by Chad Horohoe.

Annex/Content.hs

@@ -101,23 +101,21 @@ inAnnexSafe key = inAnnex' (fromMaybe False) (Just False) go key
 		=<< contentLockFile key
 
 #ifndef mingw32_HOST_OS
-	checkindirect f = liftIO $ openExistingLockFile f >>= check is_missing
+	checkindirect contentfile = liftIO $ checkOr is_missing contentfile
 	{- In direct mode, the content file must exist, but
-	 - the lock file often generally won't exist unless a removal is in
-	 - process. This does not create the lock file, it only checks for
-	 - it. -}
+	 - the lock file generally won't exist unless a removal is in
+	 - process. -}
 	checkdirect contentfile lockfile = liftIO $
 		ifM (doesFileExist contentfile)
-			( openExistingLockFile lockfile >>= check is_unlocked
+			( checkOr is_unlocked lockfile
 			, return is_missing
 			)
-	check _ (Just h) = do
-		v <- getLock h (ReadLock, AbsoluteSeek, 0, 0)
-		closeFd h
+	checkOr def lockfile = do
+		v <- checkLocked lockfile
 		return $ case v of
-			Just _ -> is_locked
-			Nothing -> is_unlocked
-	check def Nothing = return def
+			Nothing -> def
+			Just True -> is_locked
+			Just False -> is_unlocked
 #else
 	checkindirect f = liftIO $ ifM (doesFileExist f)
 		( do
@@ -161,7 +159,7 @@ lockContent key a = do
 	contentfile <- calcRepo $ gitAnnexLocation key
 	lockfile <- contentLockFile key
 	maybe noop setuplockfile lockfile
-	bracket (liftIO $ lock contentfile lockfile) (unlock lockfile) (const a)
+	bracket (lock contentfile lockfile) (unlock lockfile) (const a)
   where
 	alreadylocked = error "content is locked"
 	setuplockfile lockfile = modifyContent lockfile $
@@ -171,8 +169,11 @@ lockContent key a = do
 		void $ liftIO $ tryIO $
 			nukeFile lockfile
 #ifndef mingw32_HOST_OS
-	lock contentfile Nothing = opencontentforlock contentfile >>= dolock
-	lock _ (Just lockfile) = createLockFile Nothing lockfile >>= dolock . Just
+	lock contentfile Nothing = liftIO $
+		opencontentforlock contentfile >>= dolock
+	lock _ (Just lockfile) = do
+		mode <- annexFileMode
+		liftIO $ createLockFile mode lockfile >>= dolock . Just
 	{- Since content files are stored with the write bit disabled, have
 	 - to fiddle with permissions to open for an exclusive lock. -}
 	opencontentforlock f = catchDefaultIO Nothing $ 
@@ -189,7 +190,8 @@ lockContent key a = do
 		maybe noop cleanuplockfile mlockfile
 		liftIO $ maybe noop closeFd mfd
 #else
-	lock _ (Just lockfile) = maybe alreadylocked (return . Just) =<< lockExclusive lockfile
+	lock _ (Just lockfile) = liftIO $
+		maybe alreadylocked (return . Just) =<< lockExclusive lockfile
 	lock _ Nothing = return Nothing
 	unlock mlockfile mlockhandle = do
 		liftIO $ maybe noop dropLock mlockhandle

Annex/Ssh.hs

@@ -152,13 +152,12 @@ sshCleanup = mapM_ cleanup =<< enumSocketFiles
 		let lockfile = socket2lock socketfile
 		unlockFile lockfile
 		mode <- annexFileMode
-		fd <- liftIO $ noUmask mode $ createLockFile (Just mode) lockfile
-		v <- liftIO $ tryIO $
-			setLock fd (WriteLock, AbsoluteSeek, 0, 0)
+		v <- liftIO $ noUmask mode $ tryLockExclusive (Just mode) lockfile
 		case v of
-			Left _ -> noop
-			Right _ -> forceStopSsh socketfile
-		liftIO $ closeFd fd
+			Nothing -> noop
+			Just lck -> do
+				forceStopSsh socketfile
+				liftIO $ dropLock lck
 #else
 		forceStopSsh socketfile
 #endif

Remote/Helper/Hooks.hs

@@ -83,18 +83,12 @@ runHooks r starthook stophook a = do
 		unlockFile lck
 #ifndef mingw32_HOST_OS
 		mode <- annexFileMode
-		fd <- liftIO $ noUmask mode $ createLockFile (Just mode) lck
-		v <- liftIO $ tryIO $
-			setLock fd (WriteLock, AbsoluteSeek, 0, 0)
-		case v of
-			Left _ -> noop
-			Right _ -> run stophook
-		liftIO $ closeFd fd
+		v <- liftIO $ noUmask mode $ tryLockExclusive (Just mode) lck
 #else
 		v <- liftIO $ lockExclusive lck
+#endif
 		case v of
 			Nothing -> noop
 			Just lockhandle -> do
 				run stophook
 				liftIO $ dropLock lockhandle
-#endif

Utility/LockFile/Posix.hs

@@ -9,15 +9,21 @@ module Utility.LockFile.Posix (
 	LockHandle,
 	lockShared,
 	lockExclusive,
-	dropLock,
+	tryLockExclusive,
 	createLockFile,
 	openExistingLockFile,
+	isLocked,
+	checkLocked,
+	dropLock,
 ) where
 
 import Utility.Exception
+import Utility.Applicative
 
 import System.IO
 import System.Posix
+import Data.Maybe
+import Control.Applicative
 
 type LockFile = FilePath
 
@@ -31,27 +37,55 @@ lockShared = lock ReadLock
 lockExclusive :: Maybe FileMode -> LockFile -> IO LockHandle
 lockExclusive = lock WriteLock
 
--- The FileMode is used when creating a new lock file.
+-- Tries to take an exclusive lock, but does not block.
+tryLockExclusive :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle)
+tryLockExclusive mode lockfile = do
+	l <- openLockFile mode lockfile
+	v <- tryIO $ setLock l (WriteLock, AbsoluteSeek, 0, 0)
+	case v of
+		Left _ -> do
+			closeFd l
+			return Nothing
+		Right _ -> return $ Just $ LockHandle l
+
+-- Setting the FileMode allows creation of a new lock file.
+-- If it's Nothing then this only succeeds when the lock file already exists.
 lock :: LockRequest -> Maybe FileMode -> LockFile -> IO LockHandle
 lock lockreq mode lockfile = do
-	l <- createLockFile mode lockfile
+	l <- openLockFile mode lockfile
 	waitToSetLock l (lockreq, AbsoluteSeek, 0, 0)
 	return (LockHandle l)
 
 -- Create and opens lock file; does not lock it.
-createLockFile :: Maybe FileMode -> LockFile -> IO Fd
-createLockFile = openLockFile ReadWrite
+createLockFile :: FileMode -> LockFile -> IO Fd
+createLockFile filemode = openLockFile (Just filemode)
 
--- Opens an existing lock file; does not lock it or create it.
+-- Opens an existing lock file; does not lock it, and if it does not exist,
+-- returns Nothing.
 openExistingLockFile :: LockFile -> IO (Maybe Fd)
-openExistingLockFile = catchMaybeIO . openLockFile ReadOnly Nothing
+openExistingLockFile = catchMaybeIO . openLockFile Nothing
 
 -- Close on exec flag is set so child processes do not inherit the lock.
-openLockFile :: OpenMode -> Maybe FileMode -> LockFile -> IO Fd
-openLockFile openmode filemode lockfile = do
-	l <- openFd lockfile openmode filemode defaultFileFlags
+openLockFile :: Maybe FileMode -> LockFile -> IO Fd
+openLockFile filemode lockfile = do
+	l <- openFd lockfile ReadWrite filemode defaultFileFlags
 	setFdOption l CloseOnExec True
 	return l
 
+-- Check if a file is locked, either exclusively, or with shared lock.
+-- When the file doesn't exist, it's considered not locked.
+isLocked :: LockFile -> IO Bool
+isLocked = fromMaybe False <$$> checkLocked
+
+checkLocked :: LockFile -> IO (Maybe Bool)
+checkLocked lockfile = go =<< catchMaybeIO open
+  where
+	open = openFd lockfile ReadOnly Nothing defaultFileFlags
+	go Nothing = return Nothing
+	go (Just h) = do
+		ret <- isJust <$> getLock h (ReadLock, AbsoluteSeek, 0, 0)
+		closeFd h
+		return $ Just ret
+
 dropLock :: LockHandle -> IO ()
 dropLock (LockHandle fd) = closeFd fd