pid locking configuration and abstraction layer for git-annex

(not actually used anywhere yet)

Annex/LockPool/PosixOrPid.hs

@@ -0,0 +1,74 @@
+{- Wraps Utility.LockPool, making pid locks be used when git-annex is so
+ - configured.
+ -
+ - Copyright 2015 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.LockPool.PosixOrPid where
+
+import Common.Annex
+import qualified Annex
+import qualified Utility.LockPool.Posix as Posix
+import qualified Utility.LockPool.PidLock as Pid
+import Utility.LockFile.Posix (openLockFile)
+import Utility.LockPool.STM (LockFile)
+import Utility.LockPool.LockHandle
+import Utility.LockFile.LockStatus
+
+import System.Posix
+
+lockShared :: Maybe FileMode -> LockFile -> Annex LockHandle
+lockShared m f = pidLock m f $ Posix.lockShared m f
+
+lockExclusive :: Maybe FileMode -> LockFile -> Annex LockHandle
+lockExclusive m f = pidLock m f $ Posix.lockExclusive m f
+
+tryLockShared :: Maybe FileMode -> LockFile -> Annex (Maybe LockHandle)
+tryLockShared m f = tryPidLock m f $ Posix.tryLockShared m f
+
+tryLockExclusive :: Maybe FileMode -> LockFile -> Annex (Maybe LockHandle)
+tryLockExclusive m f = tryPidLock m f $ Posix.tryLockExclusive m f
+
+checkLocked :: LockFile -> Annex (Maybe Bool)
+checkLocked f = Posix.checkLocked f
+	`pidLockCheck` Pid.checkLocked
+
+getLockStatus :: LockFile -> Annex LockStatus
+getLockStatus f = Posix.getLockStatus f
+	`pidLockCheck` Pid.getLockStatus
+
+pidLockFile :: Annex (Maybe FilePath)
+pidLockFile = ifM (annexPidLock <$> Annex.getGitConfig)
+	( Just <$> fromRepo gitAnnexPidLockFile
+	, pure Nothing
+	)
+
+pidLockCheck :: IO a -> (LockFile -> IO a) -> Annex a
+pidLockCheck posixcheck pidcheck = 
+	liftIO . maybe posixcheck pidcheck =<< pidLockFile
+
+pidLock :: Maybe FileMode -> LockFile -> IO LockHandle -> Annex LockHandle
+pidLock m f posixlock = go =<< pidLockFile
+  where
+	go Nothing = liftIO posixlock
+	go (Just pidlock) = do
+		timeout <- annexPidLockTimeout <$> Annex.getGitConfig
+		liftIO $ do
+			dummyPosixLock m f
+			Pid.waitLock timeout pidlock
+
+tryPidLock :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle) -> Annex (Maybe LockHandle)
+tryPidLock m f posixlock = liftIO . go =<< pidLockFile
+  where
+	go Nothing = posixlock
+	go (Just pidlock) = do
+		dummyPosixLock m f
+		Pid.tryLock pidlock
+
+-- The posix lock file is created even when using pid locks, in order to
+-- avoid complicating any code that might expect to be able to see that
+-- lock file.
+dummyPosixLock :: Maybe FileMode -> LockFile -> IO ()
+dummyPosixLock m f = closeFd =<< openLockFile ReadLock m f