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Affirmer understands and acknowledges that Creative Commons is not a + party to this document and has no duty or obligation with respect to + this CC0 or use of the Work. diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/System/FileLock.hs b/System/FileLock.hs new file mode 100644 --- /dev/null +++ b/System/FileLock.hs @@ -0,0 +1,82 @@ +{-# LANGUAGE DeriveDataTypeable #-} +{-# LANGUAGE CPP #-} + +-- | This module provides a portable interface to file locks as a mechanism for +-- inter-process synchronization. +-- +-- Each file lock is associated with a file. When taking a lock, the assiciated +-- file is created if it's not present, then the file is locked in an +-- OS-dependent way. While the lock is being held, no other process or +-- thread can take it, unless the specified 'SharedExclusive' values +-- allow it. +-- +-- All locks held by a process are released when the process exits. They can +-- also be explicitly released using 'unlockFile'. +-- +-- It is not recommended to open or otherwise use lock files for other +-- purposes, because it tends to expose differences between operating systems. +-- For example, on Windows 'System.IO.openFile' for a lock file will fail when +-- the lock is held, but on Unix it won't. +-- +-- Note on the implementation: currently the module uses flock(2) on non-Windows +-- platforms, and LockFileEx on Windows. +module System.FileLock + ( FileLock + , SharedExclusive(..) + , lockFile + , tryLockFile + , unlockFile + , withFileLock + ) where + +import Control.Applicative +import qualified Control.Exception as E +import Control.Monad +import Data.IORef +import Data.Traversable (traverse) +import Data.Typeable + +#ifdef USE_FLOCK +import qualified System.FileLock.Internal.Flock as I +#elif USE_LOCKFILEEX +import qualified System.FileLock.Internal.LockFileEx as I +#else +#error No backend is available +#endif + +-- | A token that represents ownership of a lock. +data FileLock = Lock + {-# UNPACk #-} !I.Lock + {-# UNPACk #-} !(IORef Bool) -- alive? + deriving (Typeable) + +instance Eq FileLock where + Lock _ x == Lock _ y = x == y + +newLock :: I.Lock -> IO FileLock +newLock x = Lock x <$> newIORef True + +-- | A type of lock to be taken. +data SharedExclusive + = Shared -- ^ Other process can hold a shared lock at the same time. + | Exclusive -- ^ No other process can hold a lock, shared or exclusive. + deriving (Show, Eq, Typeable) + +-- | Take a lock. This function blocks until the lock is available. +lockFile :: FilePath -> SharedExclusive -> IO FileLock +lockFile path mode = newLock =<< I.lock path (mode == Exclusive) + +-- | Try to take a lock. This function does not block. If the lock is not +-- immediately available, it returns Nothing. +tryLockFile :: FilePath -> SharedExclusive -> IO (Maybe FileLock) +tryLockFile path mode = traverse newLock =<< I.tryLock path (mode == Exclusive) + +-- | Release the lock. +unlockFile :: FileLock -> IO () +unlockFile (Lock l ref) = do + wasAlive <- atomicModifyIORef ref $ \old -> (False, old) + when wasAlive $ I.unlock l + +-- | Perform some action with a lock held. +withFileLock :: FilePath -> SharedExclusive -> (FileLock -> IO a) -> IO a +withFileLock path mode = E.bracket (lockFile path mode) unlockFile diff --git a/System/FileLock/Internal/Flock.hsc b/System/FileLock/Internal/Flock.hsc new file mode 100644 --- /dev/null +++ b/System/FileLock/Internal/Flock.hsc @@ -0,0 +1,66 @@ +module System.FileLock.Internal.Flock +#ifndef USE_FLOCK + () where +#else + (Lock, lock, tryLock, unlock) where + +#include + +import Control.Applicative +import qualified Control.Exception as E +import Data.Bits +import Foreign.C.Error +import Foreign.C.Types +import System.Posix.Files +import System.Posix.IO (openFd, closeFd, defaultFileFlags, OpenMode(..)) +import System.Posix.Types + +type Lock = Fd + +lock :: FilePath -> Bool -> IO Lock +lock path exclusive = do + fd <- open path + (`E.onException` closeFd fd) $ do + True <- flock fd exclusive True + return fd + +tryLock :: FilePath -> Bool -> IO (Maybe Lock) +tryLock path exclusive = do + fd <- open path + (`E.onException` closeFd fd) $ do + success <- flock fd exclusive False + if success + then return $ Just $ fd + else Nothing <$ closeFd fd + +unlock :: Lock -> IO () +unlock fd = closeFd fd + +open :: FilePath -> IO Fd +open path = openFd path WriteOnly (Just stdFileMode) defaultFileFlags + +flock :: Fd -> Bool -> Bool -> IO Bool +flock (Fd fd) exclusive block = do + r <- c_flock fd $ modeOp .|. blockOp + if r == 0 + then return True -- success + else do + errno <- getErrno + case () of + _ | errno == eWOULDBLOCK + -> return False -- already taken + | errno == eINTR + -> flock (Fd fd) exclusive block + | otherwise -> throwErrno "flock" + where + modeOp = case exclusive of + False -> #{const LOCK_SH} + True -> #{const LOCK_EX} + blockOp = case block of + True -> 0 + False -> #{const LOCK_NB} + +foreign import ccall "flock" + c_flock :: CInt -> CInt -> IO CInt + +#endif /* USE_FLOCK */ diff --git a/System/FileLock/Internal/LockFileEx.hsc b/System/FileLock/Internal/LockFileEx.hsc new file mode 100644 --- /dev/null +++ b/System/FileLock/Internal/LockFileEx.hsc @@ -0,0 +1,67 @@ +module System.FileLock.Internal.LockFileEx +#ifndef USE_LOCKFILEEX + () where +#else + (Lock, lock, tryLock, unlock) where + +#include + +import Control.Applicative +import qualified Control.Exception as E +import Data.Bits +import Foreign.Marshal.Alloc +import System.Win32.File +import System.Win32.Mem +import System.Win32.Types + +type Lock = HANDLE + +lock :: FilePath -> Bool -> IO Lock +lock path exclusive = do + file <- open path + (`E.onException` closeHandle file) $ do + True <- lockFirstByte file exclusive True + return file + +tryLock :: FilePath -> Bool -> IO (Maybe Lock) +tryLock path exclusive = do + file <- open path + (`E.onException` closeHandle file) $ do + r <- lockFirstByte file exclusive False + if r + then return $ Just file + else Nothing <$ closeHandle file + +unlock :: Lock -> IO () +unlock = closeHandle + +open :: FilePath -> IO HANDLE +open path = + createFile path gENERIC_WRITE (fILE_SHARE_READ .|. fILE_SHARE_WRITE) + Nothing oPEN_ALWAYS fILE_ATTRIBUTE_NORMAL Nothing + +lockFirstByte :: HANDLE -> Bool -> Bool -> IO Bool +lockFirstByte handle exclusive block + = allocaBytes sizeof_OVERLAPPED $ \op -> do + zeroMemory op $ fromIntegral sizeof_OVERLAPPED + -- Offset and OffsetHigh fields are set to 0 by zeroMemory. + r <- c_lockFileEx handle (exFlag .|. blockFlag) 0{-reserved-} + 1{-number of bytes, lower dword-} + 0{-number of bytes, higher dword-} + op + if r + then return True -- success + else do + code <- getLastError + if code == #{const ERROR_LOCK_VIOLATION} + then return False -- already taken + else failWith "LockFileEx" code + where + exFlag = if exclusive then #{const LOCKFILE_EXCLUSIVE_LOCK} else 0 + blockFlag = if block then 0 else #{const LOCKFILE_FAIL_IMMEDIATELY} + sizeof_OVERLAPPED = #{size OVERLAPPED} + +foreign import stdcall "LockFileEx" c_lockFileEx + :: HANDLE -> DWORD -> DWORD -> DWORD -> DWORD -> LPOVERLAPPED -> IO BOOL + +#endif /* USE_LOCKFILEEX */ diff --git a/filelock.cabal b/filelock.cabal new file mode 100644 --- /dev/null +++ b/filelock.cabal @@ -0,0 +1,34 @@ +-- Initial filelock.cabal generated by cabal init. For further +-- documentation, see http://haskell.org/cabal/users-guide/ + +name: filelock +version: 0.1.0.0 +synopsis: Portable interface to file locking (flock / LockFileEx) +-- description: +homepage: http://github.com/takano-akio/filelock +license: PublicDomain +license-file: LICENSE +author: Takano Akio +maintainer: aljee@hyper.cx +-- copyright: +category: System +build-type: Simple +-- extra-source-files: +cabal-version: >=1.10 + +library + exposed-modules: System.FileLock + other-modules: System.FileLock.Internal.Flock + System.FileLock.Internal.LockFileEx + -- other-extensions: + build-depends: base >=4.5.1.0 && <4.7 + -- hs-source-dirs: + default-language: Haskell2010 + + ghc-options: -Wall + if os(windows) + cpp-options: -DUSE_LOCKFILEEX + build-depends: Win32 + else + cpp-options: -DUSE_FLOCK + build-depends: unix