lock pools to work around non-concurrency/composition safety of POSIX fcntl

Utility/LockPool/Posix.hs

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+{- Posix lock files, using lock pools.
+ -
+ - Copyright 2015 Joey Hess <id@joeyh.name>
+ -
+ - License: BSD-2-clause
+ -}
+
+module Utility.LockPool.Posix (
+	LockHandle,
+	lockShared,
+	lockExclusive,
+	tryLockExclusive,
+	checkLocked,
+	getLockStatus,
+	dropLock,
+	checkSaneLock,
+) where
+
+import qualified Utility.LockFile.Posix as F
+import qualified Utility.LockPool.STM as P
+import Utility.LockPool.STM (LockPool, LockFile, LockMode(..))
+import Utility.LockPool.LockHandle
+import Utility.Monad
+
+import Control.Concurrent.STM
+import System.IO
+import System.Posix
+import Data.Maybe
+import Control.Applicative
+import Prelude
+
+-- Takes a shared lock, blocking until the lock is available.
+lockShared :: Maybe FileMode -> LockFile -> IO LockHandle
+lockShared mode file = makeLockHandle
+	(P.waitTakeLock P.lockPool file LockShared)
+	(F.lockShared mode file)
+
+lockExclusive :: Maybe FileMode -> LockFile -> IO LockHandle
+lockExclusive mode file = makeLockHandle
+	(P.waitTakeLock P.lockPool file LockExclusive)
+	(F.lockExclusive mode file)
+
+tryLockExclusive :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle)
+tryLockExclusive mode file = tryMakeLockHandle
+	(P.tryTakeLock P.lockPool file LockExclusive)
+	(F.tryLockExclusive mode file)
+
+-- Returns Nothing when the file doesn't exist, for cases where
+-- that is different from it not being locked.
+checkLocked :: LockFile -> IO (Maybe Bool)
+checkLocked file = P.getLockStatus P.lockPool file (pure True)
+	(F.checkLocked file)
+
+getLockStatus :: LockFile -> IO (Maybe ProcessID)
+getLockStatus file = P.getLockStatus P.lockPool file getProcessID
+	(F.getLockStatus file)
+
+checkSaneLock :: LockFile -> LockHandle -> IO Bool
+checkSaneLock lockfile (LockHandle _ fh) = F.checkSaneLock lockfile fh