more zombie fighting

I'm down to 9 places in the code that can produce unwaited for zombies.

Most of these are pretty innocuous, at least for now, are only
used in short-running commands, or commands that run a set of
actions and explicitly reap zombies after each one.

The one from Annex.Branch.files could be trouble later,
since both Command.Fsck and Command.Unused can trigger it,
and the assistant will be doing those eventally. Ditto the one in
Git.LsTree.lsTree, which Command.Unused uses.

The only ones currently affecting the assistant though, are
in Git.LsFiles. Several threads use several of those.

(And yeah, using pipes or ResourceT would be a less ad-hoc approach,
but I don't really feel like ripping my entire code base apart right
now to change a foundation monad. Maybe one of these days..)

Annex/Branch.hs

@@ -261,7 +261,7 @@ files :: Annex [FilePath]
 files = do
 	update
 	withIndex $ do
-		bfiles <- inRepo $ Git.Command.pipeNullSplit
+		bfiles <- inRepo $ Git.Command.pipeNullSplitZombie
 			[Params "ls-tree --name-only -r -z", Param $ show fullname]
 		jfiles <- getJournalledFiles
 		return $ jfiles ++ bfiles

Command/Log.hs

@@ -136,7 +136,7 @@ getLog key os = do
 	top <- fromRepo Git.repoPath
 	p <- liftIO $ relPathCwdToFile top
 	let logfile = p </> Logs.Location.logFile key
-	inRepo $ pipeNullSplit $
+	inRepo $ pipeNullSplitZombie $
 		[ Params "log -z --pretty=format:%ct --raw --abbrev=40"
 		, Param "--remove-empty"
 		] ++ os ++

Git/Command.hs

@@ -8,7 +8,7 @@
 module Git.Command where
 
 import System.Posix.Process (getAnyProcessStatus)
-import System.Process
+import System.Process (std_in, env)
 
 import Common
 import Git
@@ -38,16 +38,17 @@ run subcommand params repo = assertLocal repo $
 	unlessM (runBool subcommand params repo) $
 		error $ "git " ++ subcommand ++ " " ++ show params ++ " failed"
 
-{- Runs a git subcommand and returns its output, lazily. 
+{- Runs a git subcommand and returns its output, lazily.
  -
- - Note that this leaves the git process running, and so zombies will
- - result unless reap is called.
+ - Also returns an action that should be used when the output is all
+ - read (or no more is needed), that will wait on the command, and
+ - return True if it succeeded. Failure to wait will result in zombies.
  -}
-pipeReadLazy :: [CommandParam] -> Repo -> IO String
-pipeReadLazy params repo = assertLocal repo $
-	withHandle StdoutHandle createBackgroundProcess p $ \h -> do
-		fileEncoding h
-		hGetContents h
+pipeReadLazy :: [CommandParam] -> Repo -> IO (String, IO Bool)
+pipeReadLazy params repo = assertLocal repo $ do
+	(Just h, _, _, pid) <- createProcess p { std_in = CreatePipe }
+	c <- hGetContents h
+	return (c, checkSuccessProcess pid)
 	where
 		p  = gitCreateProcess params repo
 
@@ -78,19 +79,20 @@ pipeWrite :: [CommandParam] -> Repo -> (Handle -> IO ()) -> IO ()
 pipeWrite params repo = withHandle StdinHandle createProcessSuccess $
 	gitCreateProcess params repo
 
-gitCreateProcess :: [CommandParam] -> Repo -> CreateProcess
-gitCreateProcess params repo =
-	(proc "git" $ toCommand $ gitCommandLine params repo)
-			{ env = gitEnv repo }
-
 {- Reads null terminated output of a git command (as enabled by the -z 
  - parameter), and splits it. -}
-pipeNullSplit :: [CommandParam] -> Repo -> IO [String]
-pipeNullSplit params repo =
-	filter (not . null) . split sep <$> pipeReadLazy params repo
+pipeNullSplit :: [CommandParam] -> Repo -> IO ([String], IO Bool)
+pipeNullSplit params repo = do
+	(s, cleanup) <- pipeReadLazy params repo
+	return (filter (not . null) $ split sep s, cleanup)
 	where
 		sep = "\0"
 
+{- Does not wait on the git command when it's done, so produces
+ - one zombie. -}
+pipeNullSplitZombie :: [CommandParam] -> Repo -> IO [String]
+pipeNullSplitZombie params repo = fst <$> pipeNullSplit params repo
+
 {- Reaps any zombie git processes. -}
 reap :: IO ()
 reap = do
@@ -101,3 +103,8 @@ reap = do
 {- Runs a git command as a coprocess. -}
 gitCoProcessStart :: [CommandParam] -> Repo -> IO CoProcess.CoProcessHandle
 gitCoProcessStart params repo = CoProcess.start "git" (toCommand $ gitCommandLine params repo) (gitEnv repo)
+
+gitCreateProcess :: [CommandParam] -> Repo -> CreateProcess
+gitCreateProcess params repo =
+	(proc "git" $ toCommand $ gitCommandLine params repo)
+			{ env = gitEnv repo }

Git/LsFiles.hs

@@ -26,11 +26,11 @@ import Git.Sha
 
 {- Scans for files that are checked into git at the specified locations. -}
 inRepo :: [FilePath] -> Repo -> IO [FilePath]
-inRepo l = pipeNullSplit $ Params "ls-files --cached -z --" : map File l
+inRepo l = pipeNullSplitZombie $ Params "ls-files --cached -z --" : map File l
 
 {- Scans for files at the specified locations that are not checked into git. -}
 notInRepo :: Bool -> [FilePath] -> Repo -> IO [FilePath]
-notInRepo include_ignored l repo = pipeNullSplit params repo
+notInRepo include_ignored l repo = pipeNullSplitZombie params repo
 	where
 		params = [Params "ls-files --others"] ++ exclude ++
 			[Params "-z --"] ++ map File l
@@ -48,14 +48,14 @@ stagedNotDeleted :: [FilePath] -> Repo -> IO [FilePath]
 stagedNotDeleted = staged' [Param "--diff-filter=ACMRT"]
 
 staged' :: [CommandParam] -> [FilePath] -> Repo -> IO [FilePath]
-staged' ps l = pipeNullSplit $ prefix ++ ps ++ suffix
+staged' ps l = pipeNullSplitZombie $ prefix ++ ps ++ suffix
 	where
 		prefix = [Params "diff --cached --name-only -z"]
 		suffix = Param "--" : map File l
 
 {- Returns a list of files that have unstaged changes. -}
 changedUnstaged :: [FilePath] -> Repo -> IO [FilePath]
-changedUnstaged l = pipeNullSplit params
+changedUnstaged l = pipeNullSplitZombie params
 	where
 		params = Params "diff --name-only -z --" : map File l
 
@@ -71,7 +71,7 @@ typeChanged = typeChanged' []
 
 typeChanged' :: [CommandParam] -> [FilePath] -> Repo -> IO [FilePath]
 typeChanged' ps l repo = do
-	fs <- pipeNullSplit (prefix ++ ps ++ suffix) repo
+	fs <- pipeNullSplitZombie (prefix ++ ps ++ suffix) repo
 	-- git diff returns filenames relative to the top of the git repo;
 	-- convert to filenames relative to the cwd, like git ls-files.
 	let top = repoPath repo
@@ -108,7 +108,8 @@ unmerged :: [FilePath] -> Repo -> IO [Unmerged]
 unmerged l repo = reduceUnmerged [] . catMaybes . map parseUnmerged <$> list repo
 	where
 		files = map File l
-		list = pipeNullSplit $ Params "ls-files --unmerged -z --" : files
+		list = pipeNullSplitZombie $
+			Params "ls-files --unmerged -z --" : files
 
 data InternalUnmerged = InternalUnmerged
 	{ isus :: Bool

Git/LsTree.hs

@@ -30,7 +30,7 @@ data TreeItem = TreeItem
 {- Lists the contents of a Ref -}
 lsTree :: Ref -> Repo -> IO [TreeItem]
 lsTree t repo = map parseLsTree <$>
-	pipeNullSplit [Params "ls-tree --full-tree -z -r --", File $ show t] repo
+	pipeNullSplitZombie [Params "ls-tree --full-tree -z -r --", File $ show t] repo
 
 {- Parses a line of ls-tree output.
  - (The --long format is not currently supported.) -}

Git/UnionMerge.hs

@@ -58,9 +58,11 @@ diffOpts = ["--raw", "-z", "-r", "--no-renames", "-l0"]
 {- Streams update-index changes to perform a merge,
  - using git to get a raw diff. -}
 doMerge :: CatFileHandle -> [String] -> Repo -> Streamer
-doMerge ch differ repo streamer = gendiff >>= go
+doMerge ch differ repo streamer = do
+	(diff, cleanup) <- pipeNullSplit (map Param differ) repo
+	go diff
+	void $ cleanup
 	where
-		gendiff = pipeNullSplit (map Param differ) repo
 		go [] = noop
 		go (info:file:rest) = mergeFile info file ch repo >>=
 			maybe (go rest) (\l -> streamer l >> go rest)

Git/UpdateIndex.hs

@@ -48,7 +48,10 @@ streamUpdateIndex repo as = pipeWrite params repo $ \h -> do
 {- A streamer that adds the current tree for a ref. Useful for eg, copying
  - and modifying branches. -}
 lsTree :: Ref -> Repo -> Streamer
-lsTree (Ref x) repo streamer = mapM_ streamer =<< pipeNullSplit params repo
+lsTree (Ref x) repo streamer = do
+	(s, cleanup) <- pipeNullSplit params repo
+	mapM_ streamer s
+	void $ cleanup
 	where
 		params = map Param ["ls-tree", "-z", "-r", "--full-tree", x]