System.IO.LockFile.Internal

Low-level API for providing exclusive access to a resource using lock file.

Locking primitives

lock :: (MonadMask m, MonadIO m) => LockingParameters -> FilePath -> m Handle

Open lock file write PID of a current process in to it and return its handle.

If operation doesn't succeed, then LockingException is raised. See also LockingParameters and RetryStrategy for details.

unlock :: (MonadMask m, MonadIO m) => FilePath -> Handle -> m ()

Close lock file handle and then delete it.

Configuration

data LockingParameters

Locking algorithm parameters. When in doubt, use def, otherwise start with it. Example:

lockedDo
    :: (MonadMask m, MonadIO m)
    => FilePath
    -> m a
    -> m a
lockedDo = withLockFile lockParams lockFile
  where
    lockParams = def
        { retryToAcquireLock = NumberOfTimes 3
        }

    lockFile = withLockExt "/var/lock/my-app"

Constructors

LockingParameters

Fields

• retryToAcquireLock :: !RetryStrategy

  Strategy for handling situations when lock-file is already acquired.

• sleepBetweenRetries :: !Word64

  Sleep interval in microseconds.

Instances

Eq LockingParameters

Methods

(==) :: LockingParameters -> LockingParameters -> Bool

(/=) :: LockingParameters -> LockingParameters -> Bool

Data LockingParameters

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> LockingParameters -> c LockingParameters

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c LockingParameters

toConstr :: LockingParameters -> Constr

dataTypeOf :: LockingParameters -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c LockingParameters)

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c LockingParameters)

gmapT :: (forall b. Data b => b -> b) -> LockingParameters -> LockingParameters

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> LockingParameters -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> LockingParameters -> r

gmapQ :: (forall d. Data d => d -> u) -> LockingParameters -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> LockingParameters -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> LockingParameters -> m LockingParameters

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> LockingParameters -> m LockingParameters

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> LockingParameters -> m LockingParameters

Read LockingParameters

Methods

readsPrec :: Int -> ReadS LockingParameters

readList :: ReadS [LockingParameters]

readPrec :: ReadPrec LockingParameters

readListPrec :: ReadPrec [LockingParameters]

Show LockingParameters

Methods

showsPrec :: Int -> LockingParameters -> ShowS

show :: LockingParameters -> String

showList :: [LockingParameters] -> ShowS

Generic LockingParameters

Associated Types

type Rep LockingParameters :: * -> *

Methods

from :: LockingParameters -> Rep LockingParameters x

to :: Rep LockingParameters x -> LockingParameters

Default LockingParameters

Defined as:

def = LockingParameters
    { retryToAcquireLock  = def
    , sleepBetweenRetries = 8000000  -- 8 seconds
    }

Sleep interval is inspired by lockfile command line utility that is part of Procmail.

Methods

def :: LockingParameters

type Rep LockingParameters

type Rep LockingParameters = D1 * (MetaData "LockingParameters" "System.IO.LockFile.Internal" "lock-file-0.7.0.0-HyF0nY0IvY2Cpy0LnOwds2" False) (C1 * (MetaCons "LockingParameters" PrefixI True) ((:*:) * (S1 * (MetaSel (Just Symbol "retryToAcquireLock") NoSourceUnpackedness SourceStrict DecidedStrict) (Rec0 * RetryStrategy)) (S1 * (MetaSel (Just Symbol "sleepBetweenRetries") SourceUnpack SourceStrict DecidedStrict) (Rec0 * Word64))))

data RetryStrategy

Defines strategy for handling situations when lock-file is already acquired.

Constructors

No

Don't retry at all.

Indefinitely

Retry indefinitely.

NumberOfTimes !Word8

Retry only specified number of times. If equal to zero then it is interpreted same way as No.

Instances

Eq RetryStrategy

Methods

(==) :: RetryStrategy -> RetryStrategy -> Bool

(/=) :: RetryStrategy -> RetryStrategy -> Bool

Data RetryStrategy

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> RetryStrategy -> c RetryStrategy

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c RetryStrategy

toConstr :: RetryStrategy -> Constr

dataTypeOf :: RetryStrategy -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c RetryStrategy)

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c RetryStrategy)

gmapT :: (forall b. Data b => b -> b) -> RetryStrategy -> RetryStrategy

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> RetryStrategy -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> RetryStrategy -> r

gmapQ :: (forall d. Data d => d -> u) -> RetryStrategy -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> RetryStrategy -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> RetryStrategy -> m RetryStrategy

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> RetryStrategy -> m RetryStrategy

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> RetryStrategy -> m RetryStrategy

Read RetryStrategy

Methods

readsPrec :: Int -> ReadS RetryStrategy

readList :: ReadS [RetryStrategy]

readPrec :: ReadPrec RetryStrategy

readListPrec :: ReadPrec [RetryStrategy]

Show RetryStrategy

Methods

showsPrec :: Int -> RetryStrategy -> ShowS

show :: RetryStrategy -> String

showList :: [RetryStrategy] -> ShowS

Generic RetryStrategy

Associated Types

type Rep RetryStrategy :: * -> *

Methods

from :: RetryStrategy -> Rep RetryStrategy x

to :: Rep RetryStrategy x -> RetryStrategy

Default RetryStrategy

Defined as: def = Indefinitely

Methods

def :: RetryStrategy

type Rep RetryStrategy

type Rep RetryStrategy = D1 * (MetaData "RetryStrategy" "System.IO.LockFile.Internal" "lock-file-0.7.0.0-HyF0nY0IvY2Cpy0LnOwds2" False) ((:+:) * (C1 * (MetaCons "No" PrefixI False) (U1 *)) ((:+:) * (C1 * (MetaCons "Indefinitely" PrefixI False) (U1 *)) (C1 * (MetaCons "NumberOfTimes" PrefixI False) (S1 * (MetaSel (Nothing Symbol) SourceUnpack SourceStrict DecidedStrict) (Rec0 * Word8)))))

Exceptions

data LockingException

Constructors

UnableToAcquireLockFile FilePath

Wasn't able to aquire lock file specified as an argument.

CaughtIOException IOException

IOException occurred while creating or removing lock file.

Instances

Show LockingException

Methods

showsPrec :: Int -> LockingException -> ShowS

show :: LockingException -> String

showList :: [LockingException] -> ShowS

Exception LockingException

Methods

toException :: LockingException -> SomeException

fromException :: SomeException -> Maybe LockingException

displayException :: LockingException -> String