From 59672d32edd9cc30942a9200670b3e1f817d26aa Mon Sep 17 00:00:00 2001
From: Joey Hess <joey@kitenet.net>
Date: Sun, 31 Oct 2010 01:06:58 -0400
Subject: [PATCH] write to tmp file

Writing to a tmp file means no locking is needed, and it fixes a bug
introduced by the last commit, which made log files be read lazily, so
they could still be open when written, which breaks due to haskell's
internal locking.
---
 LocationLog.hs | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/LocationLog.hs b/LocationLog.hs
index 20e777c567..14ae88abc3 100644
--- a/LocationLog.hs
+++ b/LocationLog.hs
@@ -35,6 +35,7 @@ import qualified Data.Map as Map
 import System.IO
 import System.Directory
 import Data.Char
+import System.Posix.Process
 
 import qualified GitRepo as Git
 import Utility
@@ -111,19 +112,14 @@ readLog file = do
 		else do
 			return []
 
-{- Adds a LogLine to a log file -}
-appendLog :: FilePath -> LogLine -> IO ()
-appendLog file line = do
-	createDirectoryIfMissing True (parentDir file)
-	withFileLocked file AppendMode $ \h ->
-		hPutStrLn h $ show line
-
 {- Writes a set of lines to a log file -}
 writeLog :: FilePath -> [LogLine] -> IO ()
 writeLog file lines = do
+	pid <- getProcessID
+	let tmpfile = file ++ ".tmp" ++ show pid
 	createDirectoryIfMissing True (parentDir file)
-	withFileLocked file WriteMode $ \h ->
-		hPutStr h $ unlines $ map show lines
+	writeFile tmpfile $ unlines $ map show lines
+	renameFile tmpfile file
 
 {- Generates a new LogLine with the current date. -}
 logNow :: LogStatus -> UUID -> IO LogLine