diff options
Diffstat (limited to 'Utility/LockFile/Posix.hs')
| -rw-r--r-- | Utility/LockFile/Posix.hs | 39 |
1 files changed, 26 insertions, 13 deletions
diff --git a/Utility/LockFile/Posix.hs b/Utility/LockFile/Posix.hs index 18d9e4fc1..cf88fa87d 100644 --- a/Utility/LockFile/Posix.hs +++ b/Utility/LockFile/Posix.hs @@ -9,6 +9,7 @@ module Utility.LockFile.Posix ( LockHandle, lockShared, lockExclusive, + tryLockShared, tryLockExclusive, checkLocked, getLockStatus, @@ -36,31 +37,43 @@ lockShared = lock ReadLock lockExclusive :: Maybe FileMode -> LockFile -> IO LockHandle lockExclusive = lock WriteLock +-- Tries to take a shared lock, but does not block. +tryLockShared :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle) +tryLockShared = tryLock ReadLock + -- Tries to take an exclusive lock, but does not block. tryLockExclusive :: Maybe FileMode -> LockFile -> IO (Maybe LockHandle) -tryLockExclusive mode lockfile = do - l <- openLockFile mode lockfile - v <- tryIO $ setLock l (WriteLock, AbsoluteSeek, 0, 0) - case v of - Left _ -> do - closeFd l - return Nothing - Right _ -> return $ Just $ LockHandle l +tryLockExclusive = tryLock WriteLock -- Setting the FileMode allows creation of a new lock file. -- If it's Nothing then this only succeeds when the lock file already exists. lock :: LockRequest -> Maybe FileMode -> LockFile -> IO LockHandle lock lockreq mode lockfile = do - l <- openLockFile mode lockfile + l <- openLockFile lockreq mode lockfile waitToSetLock l (lockreq, AbsoluteSeek, 0, 0) return (LockHandle l) +-- Tries to take an lock, but does not block. +tryLock :: LockRequest -> Maybe FileMode -> LockFile -> IO (Maybe LockHandle) +tryLock lockreq mode lockfile = do + l <- openLockFile lockreq mode lockfile + v <- tryIO $ setLock l (lockreq, AbsoluteSeek, 0, 0) + case v of + Left _ -> do + closeFd l + return Nothing + Right _ -> return $ Just $ LockHandle l + -- Close on exec flag is set so child processes do not inherit the lock. -openLockFile :: Maybe FileMode -> LockFile -> IO Fd -openLockFile filemode lockfile = do - l <- openFd lockfile ReadWrite filemode defaultFileFlags +openLockFile :: LockRequest -> Maybe FileMode -> LockFile -> IO Fd +openLockFile lockreq filemode lockfile = do + l <- openFd lockfile openfor filemode defaultFileFlags setFdOption l CloseOnExec True return l + where + openfor = case lockreq of + ReadLock -> ReadOnly + _ -> ReadWrite -- Returns Nothing when the file doesn't exist, for cases where -- that is different from it not being locked. @@ -81,7 +94,7 @@ getLockStatus lockfile = do getLockStatus' :: LockFile -> IO (Maybe (Maybe ProcessID)) getLockStatus' lockfile = go =<< catchMaybeIO open where - open = openFd lockfile ReadOnly Nothing defaultFileFlags + open = openLockFile ReadLock Nothing lockfile go Nothing = return Nothing go (Just h) = do v <- getLock h (ReadLock, AbsoluteSeek, 0, 0) |