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{- git-annex lock files.
-
- Copyright 2012-2015 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
{-# LANGUAGE CPP #-}
module Annex.LockFile (
lockFileCached,
unlockFile,
getLockCache,
fromLockCache,
withExclusiveLock,
tryExclusiveLock,
) where
import Annex.Common
import Annex
import Types.LockCache
import qualified Git
import Annex.Perms
import Annex.LockPool
import qualified Data.Map as M
{- Create a specified lock file, and takes a shared lock, which is retained
- in the cache. -}
lockFileCached :: FilePath -> Annex ()
lockFileCached file = go =<< fromLockCache file
where
go (Just _) = noop -- already locked
go Nothing = do
#ifndef mingw32_HOST_OS
mode <- annexFileMode
lockhandle <- noUmask mode $ lockShared (Just mode) file
#else
lockhandle <- liftIO $ waitToLock $ lockShared file
#endif
changeLockCache $ M.insert file lockhandle
unlockFile :: FilePath -> Annex ()
unlockFile file = maybe noop go =<< fromLockCache file
where
go lockhandle = do
liftIO $ dropLock lockhandle
changeLockCache $ M.delete file
getLockCache :: Annex LockCache
getLockCache = getState lockcache
fromLockCache :: FilePath -> Annex (Maybe LockHandle)
fromLockCache file = M.lookup file <$> getLockCache
changeLockCache :: (LockCache -> LockCache) -> Annex ()
changeLockCache a = do
m <- getLockCache
changeState $ \s -> s { lockcache = a m }
{- Runs an action with an exclusive lock held. If the lock is already
- held, blocks until it becomes free. -}
withExclusiveLock :: (Git.Repo -> FilePath) -> Annex a -> Annex a
withExclusiveLock getlockfile a = do
lockfile <- fromRepo getlockfile
createAnnexDirectory $ takeDirectory lockfile
mode <- annexFileMode
bracket (lock mode lockfile) (liftIO . dropLock) (const a)
where
#ifndef mingw32_HOST_OS
lock mode = noUmask mode . lockExclusive (Just mode)
#else
lock _mode = liftIO . waitToLock . lockExclusive
#endif
{- Tries to take an exclusive lock and run an action. If the lock is
- already held, returns Nothing. -}
tryExclusiveLock :: (Git.Repo -> FilePath) -> Annex a -> Annex (Maybe a)
tryExclusiveLock getlockfile a = do
lockfile <- fromRepo getlockfile
createAnnexDirectory $ takeDirectory lockfile
mode <- annexFileMode
bracket (lock mode lockfile) (liftIO . unlock) go
where
#ifndef mingw32_HOST_OS
lock mode = noUmask mode . tryLockExclusive (Just mode)
#else
lock _mode = liftIO . lockExclusive
#endif
unlock = maybe noop dropLock
go Nothing = return Nothing
go (Just _) = Just <$> a
|
