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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02

Modulelukko-0.1.2Haskell2010

Lukko.OFD

Linux open file descriptor locking.

https://www.gnu.org/software/libc/manual/html_node/Open-File-Description-Locks.html

We prefer this over BSD locking (e.g. flock) since the latter appears to break in some NFS configurations. Note that we intentionally do not try to use ordinary POSIX file locking due to its peculiar semantics under multi-threaded environments.

Contents

Types
File descriptors
Handles

Synopsis

data FileLockingNotSupported
value fileLockingSupported
type FileLockingSupported
data FileLockingMethod
value fileLockingMethod
data LockMode
newtype FD
value fdOpen
value fdClose
value fdLock
value fdTryLock
value fdUnlock
value hLock
value hTryLock
value hUnlock

Packagelukko-0.1.2
Exports15
LanguageHaskell2010
LicenceGPL-2.0-or-later AND BSD-3-Clause
SourceOFD.hsc

Types

datadata FileLockingNotSupported

Exception thrown by hLock on non-Windows platforms that don't support flock.

FileLockingNotSupported

Instances2Show, Exception

Show FileLockingNotSupportedDefined in lukko-0.1.2 · Lukko.Internal.Types
Exception FileLockingNotSupportedDefined in lukko-0.1.2 · Lukko.Internal.Types

valuefileLockingSupported :: Bool

A constants specifying whether file locking is supported.

typetype FileLockingSupported = 'True

A type level fileLockingSupported.

datadata FileLockingMethod

Potentially availble lock methods.

Constructors

MethodOFD
open file descriptor locking
MethodFLock
BSD flock
MethodWindows
Windows locking
MethodNoOp
No-Op (throws FileLockingNotSupported)

Instances5Bounded, Enum, Eq, Ord, Show

Bounded FileLockingMethodDefined in lukko-0.1.2 · Lukko.Internal.Types
Enum FileLockingMethodDefined in lukko-0.1.2 · Lukko.Internal.Types
Eq FileLockingMethodDefined in lukko-0.1.2 · Lukko.Internal.Types
Ord FileLockingMethodDefined in lukko-0.1.2 · Lukko.Internal.Types
Show FileLockingMethodDefined in lukko-0.1.2 · Lukko.Internal.Types

valuefileLockingMethod :: FileLockingMethod

A constant specifying this method

datadata LockMode

Indicates a mode in which a file should be locked.

SharedLock ExclusiveLock

File descriptors

newtypenewtype FD

Opaque file descriptor

This is a wrapper over CInt

valuefdOpen :: FilePath -> IO FD

Open file to be used for locking.

open(path, O_RDWR | O_CREAT);

valuefdClose :: FD -> IO ()

Close lock file.

close(fd);

valuefdLock :: FD -> LockMode -> IO ()

Lock using OFD locks.

valuefdTryLock :: FD -> LockMode -> IO Bool

Try to lock using OFD locks.

valuefdUnlock :: FD -> IO ()

Unlock using OFD locks.

Handles

valuehLock :: Handle -> LockMode -> IO ()

Lock using OFD locks.

valuehTryLock :: Handle -> LockMode -> IO Bool

Try to lock using OFD locks.

valuehUnlock :: Handle -> IO ()

Unlock using OFD locks.