The lock-file package

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Provide exclusive access to a resource using lock file, which are files whose purpose is to signal by their presence that some resource is locked.

Code example can be found in System.IO.LockFile module.


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Properties

Versions0.5.0.0, 0.5.0.1, 0.5.0.2, 0.5.0.2
Dependenciesbase (>=4.5 && <4.9), data-default-class (==0.0.*), directory (>=1.1 && <1.3), exceptions (>0.6 && <0.9), tagged-exception-core (>=2.0.0.0 && <3), transformers (>=0.3 && <0.5) [details]
LicenseBSD3
Copyright(c) 2013-2015, Peter Trško
AuthorPeter Trsko
Maintainerpeter.trsko@gmail.com
CategorySystem
Home pagehttps://github.com/trskop/lock-file
Bug trackerhttps://github.com/trskop/lock-file/issues
Source repositoryhead: git clone git://github.com/trskop/lock-file.git
this: git clone git://github.com/trskop/lock-file.git(tag 0.5.0.2)
UploadedSun Jun 14 22:00:14 UTC 2015 by PeterTrsko

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Readme for lock-file-0.5.0.2

Lock File

Hackage Haskell Programming Language BSD3 License

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Description

Provide exclusive access to a resource using lock file, which are files whose purpose is to signal by their presence that some resource is locked.

Usage Example

Following example acquires lock file and then waits 1000000 micro seconds before releasing it. Note also that it is possible to specify retry strategy. Here we set it to No and therefore this code won't retry to acquire lock file after first failure.

module Main (main)
    where

import Control.Concurrent (threadDelay)
    -- From base package, but GHC specific.

import qualified Control.Monad.TaggedException as Exception (handle)
    -- From tagged-exception-core package.
    -- http://hackage.haskell.org/package/tagged-exception-core
import Data.Default.Class (Default(def))
    -- From data-default-class package, alternatively it's possible to use
    -- data-default package version 0.5.2 and above.
    -- http://hackage.haskell.org/package/data-default-class
    -- http://hackage.haskell.org/package/data-default
import System.IO.LockFile
    ( LockingParameters(retryToAcquireLock)
    , RetryStrategy(No)
    , withLockFile
    )


main :: IO ()
main = handleException
    . withLockFile lockParams lockFile $ threadDelay 1000000
  where
    lockParams = def
        { retryToAcquireLock = No
        }

    lockFile = "/var/run/lock/my-example-lock"

    handleException = Exception.handle
        $ putStrLn . ("Locking failed with: " ++) . show

This command line example shows that trying to execute two instances of example at the same time will result in failure of the second one.

$ ghc example.hs
[1 of 1] Compiling Main             ( example.hs, example.o )
Linking example ...
$ ./example & ./example
[1] 7893
Locking failed with: Unable to acquire lock file: "/var/run/lock/my-example-lock"
$ [1]+  Done                    ./example

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