GHC.IO.Handle.Lock

Documentation

data FileLockingNotSupported

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

Since: base-4.10.0.0

Constructors

FileLockingNotSupported

Instances

Exception FileLockingNotSupported

Defined in GHC.Internal.IO.Handle.Lock.Common

Methods

toException :: FileLockingNotSupported -> SomeException

fromException :: SomeException -> Maybe FileLockingNotSupported

displayException :: FileLockingNotSupported -> String

backtraceDesired :: FileLockingNotSupported -> Bool

Show FileLockingNotSupported

Since: base-4.10.0.0

Defined in GHC.Internal.IO.Handle.Lock.Common

Methods

showsPrec :: Int -> FileLockingNotSupported -> ShowS

show :: FileLockingNotSupported -> String

showList :: [FileLockingNotSupported] -> ShowS

data LockMode

Indicates a mode in which a file should be locked.

Constructors

SharedLock

ExclusiveLock

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

If a Handle references a file descriptor, attempt to lock contents of the underlying file in appropriate mode. If the file is already locked in incompatible mode, this function blocks until the lock is established. The lock is automatically released upon closing a Handle.

Things to be aware of:

1) This function may block inside a C call. If it does, in order to be able to interrupt it with asynchronous exceptions and/or for other threads to continue working, you MUST use threaded version of the runtime system.

2) The implementation uses LockFileEx on Windows and flock otherwise, hence all of their caveats also apply here.

3) On non-Windows platforms that don't support flock (e.g. Solaris) this function throws FileLockingNotImplemented. We deliberately choose to not provide fcntl based locking instead because of its broken semantics.

Since: base-4.10.0.0

hTryLock :: Handle -> LockMode -> IO Bool

Non-blocking version of hLock.

Returns True if taking the lock was successful and False otherwise.

Since: base-4.10.0.0

hUnlock :: Handle -> IO ()

Release a lock taken with hLock or hTryLock.

Since: base-4.11.0.0