48 lines
1.2 KiB
Haskell
48 lines
1.2 KiB
Haskell
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{- Posix lock files
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-
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- Copyright 2014 Joey Hess <joey@kitenet.net>
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-
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- License: BSD-2-clause
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-}
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module Utility.LockFile.Posix (
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lockShared,
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lockExclusive,
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dropLock,
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createLockFile,
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LockHandle
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) where
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import System.IO
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import System.Posix
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type LockFile = FilePath
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newtype LockHandle = LockHandle Fd
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-- Takes a shared lock, blocking until the lock is available.
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lockShared :: Maybe FileMode -> LockFile -> IO LockHandle
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lockShared = lock ReadLock
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-- Takes an exclusive lock, blocking until the lock is available.
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lockExclusive :: Maybe FileMode -> LockFile -> IO LockHandle
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lockExclusive = lock WriteLock
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-- The FileMode is used when creating a new lock file.
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lock :: LockRequest -> Maybe FileMode -> LockFile -> IO LockHandle
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lock lockreq mode lockfile = do
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l <- createLockFile mode lockfile
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waitToSetLock l (lockreq, AbsoluteSeek, 0, 0)
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return (LockHandle l)
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-- Create and opens lock file, does not lock it.
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-- Close on exec flag is set so child processes do not inherit the lock.
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createLockFile :: Maybe FileMode -> LockFile -> IO Fd
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createLockFile mode lockfile = do
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l <- openFd lockfile ReadWrite mode defaultFileFlags
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setFdOption l CloseOnExec True
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return l
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dropLock :: LockHandle -> IO ()
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dropLock (LockHandle fd) = closeFd fd
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