ed0afbc36b
Seem there are several races that happen when 2 threads run PidLock.tryLock at the same time. One involves checkSaneLock of the side lock file, which may be deleted by another process that is dropping the lock, causing checkSaneLock to fail. And even with the deletion disabled, it can still fail, Probably due to linkToLock failing when a second thread overwrites the lock file. The same can happen when 2 processes do, but then one process just fails to take the lock, which is fine. But with 2 threads, some actions where failing even though the process as a whole had the pid lock held. Utility.LockPool.PidLock already maintains a STM lock, and since it uses LockShared, 2 threads can hold the pidlock at the same time, and when the first thread drops the lock, it will remain held by the second thread, and so the pid lock file should not get deleted until the last thread to hold it drops the lock. Which is the right behavior, and why a LockShared STM lock is used in the first place. The problem is that each time it takes the STM lock, it then also calls PidLock.tryLock. So that was getting called repeatedly and concurrently. Fixed by noticing when the shared lock is already held, and stop calling PidLock.tryLock again, just use the pid lock that already exists then. Also, LockFile.PidLock.tryLock was deleting the pid lock when it failed to take the lock, which was entirely wrong. It should only drop the side lock. Sponsored-by: Dartmouth College's Datalad project
74 lines
2.2 KiB
Haskell
74 lines
2.2 KiB
Haskell
{- Posix lock files, using lock pools.
|
|
-
|
|
- Copyright 2015 Joey Hess <id@joeyh.name>
|
|
-
|
|
- License: BSD-2-clause
|
|
-}
|
|
|
|
module Utility.LockPool.Posix (
|
|
P.LockFile,
|
|
LockHandle,
|
|
lockShared,
|
|
lockExclusive,
|
|
tryLockShared,
|
|
tryLockExclusive,
|
|
checkLocked,
|
|
getLockStatus,
|
|
LockStatus(..),
|
|
dropLock,
|
|
checkSaneLock,
|
|
) where
|
|
|
|
import qualified Utility.LockFile.Posix as F
|
|
import Utility.LockFile.LockStatus
|
|
import qualified Utility.LockPool.STM as P
|
|
import Utility.LockPool.STM (LockFile, LockMode(..))
|
|
import Utility.LockPool.LockHandle
|
|
|
|
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.lockPool file
|
|
(\p f -> P.waitTakeLock p f LockShared)
|
|
(\f _ -> mk <$> F.lockShared mode f)
|
|
|
|
-- Takes an exclusive lock, blocking until the lock is available.
|
|
lockExclusive :: Maybe FileMode -> LockFile -> IO LockHandle
|
|
lockExclusive mode file = makeLockHandle P.lockPool file
|
|
(\p f -> P.waitTakeLock p f LockExclusive)
|
|
(\f _ -> mk <$> F.lockExclusive mode f)
|
|
|
|
-- Tries to take a shared lock, but does not block.
|
|
tryLockShared :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle)
|
|
tryLockShared mode file = tryMakeLockHandle P.lockPool file
|
|
(\p f -> P.tryTakeLock p f LockShared)
|
|
(\f _ -> fmap mk <$> F.tryLockShared mode f)
|
|
|
|
-- Tries to take an exclusive lock, but does not block.
|
|
tryLockExclusive :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle)
|
|
tryLockExclusive mode file = tryMakeLockHandle P.lockPool file
|
|
(\p f -> P.tryTakeLock p f LockExclusive)
|
|
(\f _ -> fmap mk <$> F.tryLockExclusive mode f)
|
|
|
|
-- 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 (Just True))
|
|
(F.checkLocked file)
|
|
|
|
getLockStatus :: LockFile -> IO LockStatus
|
|
getLockStatus file = P.getLockStatus P.lockPool file
|
|
(StatusLockedBy <$> getProcessID)
|
|
(F.getLockStatus file)
|
|
|
|
mk :: F.LockHandle -> FileLockOps
|
|
mk h = FileLockOps
|
|
{ fDropLock = F.dropLock h
|
|
, fCheckSaneLock = \f -> F.checkSaneLock f h
|
|
}
|