another memory optimisation

This time memory leaked if lots of UUIDs needed to be pretty-printed, as in
a get or drop of many files. Essentially the same strict read buffering
problem that affected the LocationLog underneath though.

uuidMap really could stand to be cached, as the uuid log is read many times
in this case. But it is a fairly edge case.

UUID.hs

@@ -26,6 +26,7 @@ import System.Cmd.Utils
 import System.IO
 import System.Directory
 import qualified Data.Map as M
+import System.Posix.Process
 
 import qualified GitRepo as Git
 import Types
@@ -111,8 +112,11 @@ describeUUID uuid desc = do
 	m <- uuidMap
 	let m' = M.insert uuid desc m
 	log <- uuidLog
+	pid <- liftIO $ getProcessID
+        let tmplog = log ++ ".tmp" ++ show pid
 	liftIO $ createDirectoryIfMissing True (parentDir log)
-	liftIO $ withFileLocked log WriteMode (\h -> hPutStr h $ serialize m')
+	liftIO $ writeFile tmplog $ serialize m'
+	liftIO $ renameFile tmplog log
 	where
 		serialize m = unlines $ map (\(u, d) -> u++" "++d) $ M.toList m
 
@@ -120,9 +124,7 @@ describeUUID uuid desc = do
 uuidMap :: Annex (M.Map UUID String)
 uuidMap = do
 	log <- uuidLog
-	s <- liftIO $ catch
-		(withFileLocked log ReadMode $ \h -> hGetContentsStrict h)
-		(\error -> return "")
+	s <- liftIO $ catch (readFile log) (\error -> return "")
 	return $ M.fromList $ map (\l -> pair l) $ lines s
 	where
 		pair l =

Utility.hs

@@ -6,7 +6,6 @@
  -}
 
 module Utility (
-	withFileLocked,
 	hGetContentsStrict,
 	parentDir,
 	relPathCwdToDir,
@@ -28,21 +27,6 @@ import System.IO.HVFS
 import System.FilePath
 import System.Directory
 
-{- Let's just say that Haskell makes reading/writing a file with
- - file locking excessively difficult. -}
-withFileLocked file mode action = do
-	-- TODO: find a way to use bracket here
-	handle <- openFile file mode
-	lockfd <- handleToFd handle -- closes handle
-	waitToSetLock lockfd (lockType mode, AbsoluteSeek, 0, 0)
-	handle' <- fdToHandle lockfd
-	ret <- action handle'
-	hClose handle'
-	return ret
-		where
-			lockType ReadMode = ReadLock
-			lockType _ = WriteLock
-
 {- A version of hgetContents that is not lazy. Ensures file is 
  - all read before it gets closed. -}
 hGetContentsStrict h  = hGetContents h >>= \s -> length s `seq` return s