git-annex/Annex/LockPool.hs

{- git-annex lock pool
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

{-# LANGUAGE CPP #-}

module Annex.LockPool where

import qualified Data.Map as M
import System.Posix.Types (Fd)

import Common.Annex
import Annex
import Annex.Perms

{- Create a specified lock file, and takes a shared lock. -}
lockFile :: FilePath -> Annex ()
lockFile file = go =<< fromPool file
  where
	go (Just _) = noop -- already locked
	go Nothing = do
#ifndef __WINDOWS__
		mode <- annexFileMode
		fd <- liftIO $ noUmask mode $
			openFd file ReadOnly (Just mode) defaultFileFlags
		liftIO $ waitToSetLock fd (ReadLock, AbsoluteSeek, 0, 0)
#else
		liftIO $ writeFile file ""
		let fd = 0
#endif
		changePool $ M.insert file fd

unlockFile :: FilePath -> Annex ()
unlockFile file = maybe noop go =<< fromPool file
  where
	go fd = do
#ifndef __WINDOWS__
		liftIO $ closeFd fd
#endif
		changePool $ M.delete file

getPool :: Annex (M.Map FilePath Fd)
getPool = getState lockpool

fromPool :: FilePath -> Annex (Maybe Fd)
fromPool file = M.lookup file <$> getPool

changePool :: (M.Map FilePath Fd -> M.Map FilePath Fd) -> Annex ()
changePool a = do
	m <- getPool
	changeState $ \s -> s { lockpool = a m }