move DaemonStatus manipulation out of the Annex monad to IO

I've convinced myself that nothing in DaemonStatus can deadlock,
as it always keepts the TMVar full. That was the only reason it was in the
Annex monad.

Assistant.hs

@@ -65,10 +65,8 @@
  - 	Annex monad in IO actions run by the watcher and committer
  - 	threads. Thus, a single state is shared amoung the threads, and
  - 	only one at a time can access it.
- - DaemonStatusHandle: (MVar)
- - 	The daemon's current status. This MVar should only be manipulated
- - 	from inside the Annex monad, which ensures it's accessed only
- - 	after the ThreadState MVar.
+ - DaemonStatusHandle: (STM TMVar)
+ - 	The daemon's current status.
  - ChangeChan: (STM TChan)
  - 	Changes are indicated by writing to this channel. The committer
  - 	reads from it.

Assistant/DaemonStatus.hs

@@ -15,7 +15,7 @@ import Utility.NotificationBroadcaster
 import Logs.Transfer
 import qualified Command.Sync
 
-import Control.Concurrent
+import Control.Concurrent.STM
 import System.Posix.Types
 import Data.Time.Clock.POSIX
 import Data.Time
@@ -41,7 +41,8 @@ data DaemonStatus = DaemonStatus
 
 type TransferMap = M.Map Transfer TransferInfo
 
-type DaemonStatusHandle = MVar DaemonStatus
+{- This TMVar is never left empty, so accessing it will never block. -}
+type DaemonStatusHandle = TMVar DaemonStatus
 
 newDaemonStatus :: IO DaemonStatus
 newDaemonStatus = do
@@ -56,21 +57,19 @@ newDaemonStatus = do
 		, notificationBroadcaster = nb
 		}
 
-getDaemonStatus :: DaemonStatusHandle -> Annex DaemonStatus
-getDaemonStatus = liftIO . readMVar
+getDaemonStatus :: DaemonStatusHandle -> IO DaemonStatus
+getDaemonStatus = atomically . readTMVar
 
-modifyDaemonStatus_ :: DaemonStatusHandle -> (DaemonStatus -> DaemonStatus) -> Annex ()
-modifyDaemonStatus_ handle a = do
-	nb <- liftIO $ modifyMVar handle $ \s -> return
-		(a s, notificationBroadcaster s)
-	liftIO $ sendNotification nb
+modifyDaemonStatus_ :: DaemonStatusHandle -> (DaemonStatus -> DaemonStatus) -> IO ()
+modifyDaemonStatus_ handle a = modifyDaemonStatus handle $ \s -> (a s, ())
 
-modifyDaemonStatus :: DaemonStatusHandle -> (DaemonStatus -> (DaemonStatus, b)) -> Annex b
+modifyDaemonStatus :: DaemonStatusHandle -> (DaemonStatus -> (DaemonStatus, b)) -> IO b
 modifyDaemonStatus handle a = do
-	(b, nb) <- liftIO $ modifyMVar handle $ \s -> do
-		let (s', b) = a s
-		return $ (s', (b, notificationBroadcaster s))
-	liftIO $ sendNotification nb
+	(b, nb) <- atomically $ do
+		(s, b) <- a <$> takeTMVar handle
+		putTMVar handle s
+		return $ (b, notificationBroadcaster s)
+	sendNotification nb
 	return b
 
 {- Updates the cached ordered list of remotes from the list in Annex
@@ -78,10 +77,10 @@ modifyDaemonStatus handle a = do
 updateKnownRemotes :: DaemonStatusHandle -> Annex ()
 updateKnownRemotes dstatus = do
 	remotes <- Command.Sync.syncRemotes []
-	modifyDaemonStatus_ dstatus $
+	liftIO $ modifyDaemonStatus_ dstatus $
 		\s -> s { knownRemotes = remotes }
 
-{- Load any previous daemon status file, and store it in the MVar for this
+{- Load any previous daemon status file, and store it in a MVar for this
  - process to use as its DaemonStatus. Also gets current transfer status. -}
 startDaemonStatus :: Annex DaemonStatusHandle
 startDaemonStatus = do
@@ -90,7 +89,7 @@ startDaemonStatus = do
 		catchDefaultIO (readDaemonStatusFile file) =<< newDaemonStatus
 	transfers <- M.fromList <$> getTransfers
 	remotes <- Command.Sync.syncRemotes []
-	liftIO $ newMVar status
+	liftIO $ atomically $ newTMVar status
 		{ scanComplete = False
 		, sanityCheckRunning = False
 		, currentTransfers = transfers
@@ -102,18 +101,17 @@ startDaemonStatus = do
  -}
 daemonStatusThread :: ThreadState -> DaemonStatusHandle -> IO ()
 daemonStatusThread st handle = do
-	bhandle <- runThreadState st $ 
-		liftIO . newNotificationHandle
-			=<< notificationBroadcaster <$> getDaemonStatus handle
+	bhandle <- newNotificationHandle
+		=<< notificationBroadcaster <$> getDaemonStatus handle
 	checkpoint
 	runEvery (Seconds tenMinutes) $ do
-		liftIO $ waitNotification bhandle
+		waitNotification bhandle
 		checkpoint
 	where
-		checkpoint = runThreadState st $ do
-			file <- fromRepo gitAnnexDaemonStatusFile
+		checkpoint = do
 			status <- getDaemonStatus handle
-			liftIO $ writeDaemonStatusFile file status
+			file <- runThreadState st $ fromRepo gitAnnexDaemonStatusFile
+			writeDaemonStatusFile file status
 
 {- Don't just dump out the structure, because it will change over time,
  - and parts of it are not relevant. -}
@@ -167,12 +165,12 @@ tenMinutes :: Int
 tenMinutes = 10 * 60
 
 {- Mutates the transfer map. -}
-adjustTransfers :: DaemonStatusHandle -> (TransferMap -> TransferMap) -> Annex ()
+adjustTransfers :: DaemonStatusHandle -> (TransferMap -> TransferMap) -> IO ()
 adjustTransfers dstatus a = modifyDaemonStatus_ dstatus $
 	\s -> s { currentTransfers = a (currentTransfers s) }
 
 {- Removes a transfer from the map, and returns its info. -}
-removeTransfer :: DaemonStatusHandle -> Transfer -> Annex (Maybe TransferInfo)
+removeTransfer :: DaemonStatusHandle -> Transfer -> IO (Maybe TransferInfo)
 removeTransfer dstatus t = modifyDaemonStatus dstatus go
 	where
 		go s =

Assistant/Threads/Pusher.hs

@@ -51,8 +51,7 @@ pushThread st daemonstatus commitchan pushmap = do
 		now <- getCurrentTime
 		if shouldPush now commits
 			then do
-				remotes <- runThreadState st $
-					knownRemotes <$> getDaemonStatus daemonstatus
+				remotes <- knownRemotes <$> getDaemonStatus daemonstatus
 				pushToRemotes thisThread now st (Just pushmap) remotes
 			else do
 				debug thisThread

Assistant/Threads/SanityChecker.hs

@@ -26,32 +26,28 @@ thisThread = "SanityChecker"
 {- This thread wakes up occasionally to make sure the tree is in good shape. -}
 sanityCheckerThread :: ThreadState -> DaemonStatusHandle -> TransferQueue -> ChangeChan -> IO ()
 sanityCheckerThread st status transferqueue changechan = forever $ do
-	waitForNextCheck st status
+	waitForNextCheck status
 
 	debug thisThread ["starting sanity check"]
 
-	runThreadState st $
-		modifyDaemonStatus_ status $ \s -> s
-				{ sanityCheckRunning = True }
+	modifyDaemonStatus_ status $ \s -> s
+		{ sanityCheckRunning = True }
 
 	now <- getPOSIXTime -- before check started
 	catchIO (check st status transferqueue changechan)
 		(runThreadState st . warning . show)
 
-	runThreadState st $ do
-		modifyDaemonStatus_ status $ \s -> s
-			{ sanityCheckRunning = False
-			, lastSanityCheck = Just now
-			}
+	modifyDaemonStatus_ status $ \s -> s
+		{ sanityCheckRunning = False
+		, lastSanityCheck = Just now
+		}
 	
 	debug thisThread ["sanity check complete"]
 
-
 {- Only run one check per day, from the time of the last check. -}
-waitForNextCheck :: ThreadState -> DaemonStatusHandle -> IO ()
-waitForNextCheck st status = do
-	v <- runThreadState st $
-		lastSanityCheck <$> getDaemonStatus status
+waitForNextCheck :: DaemonStatusHandle -> IO ()
+waitForNextCheck status = do
+	v <- lastSanityCheck <$> getDaemonStatus status
 	now <- getPOSIXTime
 	threadDelaySeconds $ Seconds $ calcdelay now v
 	where

Assistant/Threads/TransferWatcher.hs

@@ -55,12 +55,11 @@ onErr _ _ msg _ = error msg
 onAdd :: Handler
 onAdd st dstatus file _ = case parseTransferFile file of
 	Nothing -> noop
-	Just t -> do
-		runThreadState st $ go t =<< checkTransfer t
+	Just t -> go t =<< runThreadState st (checkTransfer t)
 	where
 		go _ Nothing = noop -- transfer already finished
 		go t (Just info) = do
-			liftIO $ debug thisThread
+			debug thisThread
 				[ "transfer starting:"
 				, show t
 				]
@@ -71,11 +70,11 @@ onAdd st dstatus file _ = case parseTransferFile file of
 
 {- Called when a transfer information file is removed. -}
 onDel :: Handler
-onDel st dstatus file _ = case parseTransferFile file of
+onDel _ dstatus file _ = case parseTransferFile file of
 	Nothing -> noop
 	Just t -> do
 		debug thisThread
 			[ "transfer finishing:"
 			, show t
 			]
-		void $ runThreadState st $ removeTransfer dstatus t
+		void $ removeTransfer dstatus t

Assistant/Threads/Transferrer.hs

@@ -48,7 +48,7 @@ transfererThread st dstatus transferqueue slots = go
  - being uploaded to isn't known to have the file. -}
 shouldTransfer :: DaemonStatusHandle -> Transfer -> TransferInfo -> Annex Bool
 shouldTransfer dstatus t info =
-	go =<< currentTransfers <$> getDaemonStatus dstatus
+	go =<< currentTransfers <$> liftIO (getDaemonStatus dstatus)
 	where
 		go m
 			| M.member t m = return False
@@ -84,7 +84,7 @@ transferThread st dstatus slots t info = case (transferRemote info, associatedFi
 		tid <- inTransferSlot slots st $
 			transferprocess remote file
 		now <- getCurrentTime
-		runThreadState st $ adjustTransfers dstatus $
+		adjustTransfers dstatus $
 			M.insertWith' const t info
 				{ startedTime = Just $ utcTimeToPOSIXSeconds now
 				, transferTid = Just tid

Assistant/Threads/Watcher.hs

@@ -76,8 +76,7 @@ statupScan st dstatus scanner = do
 	runThreadState st $
 		showAction "scanning"
 	r <- scanner
-	runThreadState st $
-		modifyDaemonStatus_ dstatus $ \s -> s { scanComplete = True }
+	modifyDaemonStatus_ dstatus $ \s -> s { scanComplete = True }
 
 	-- Notice any files that were deleted before watching was started.
 	runThreadState st $ do
@@ -132,7 +131,7 @@ runHandler threadname st dstatus transferqueue changechan handler file filestatu
 onAdd :: Handler
 onAdd threadname file filestatus dstatus _
 	| maybe False isRegularFile filestatus = do
-		ifM (scanComplete <$> getDaemonStatus dstatus)
+		ifM (scanComplete <$> liftIO (getDaemonStatus dstatus))
 			( go
 			, ifM (null <$> inRepo (Git.LsFiles.notInRepo False [file]))
 				( noChange
@@ -156,7 +155,7 @@ onAddSymlink threadname file filestatus dstatus transferqueue = go =<< Backend.l
 			link <- calcGitLink file key
 			ifM ((==) link <$> liftIO (readSymbolicLink file))
 				( do
-					s <- getDaemonStatus dstatus
+					s <- liftIO $ getDaemonStatus dstatus
 					checkcontent key s
 					ensurestaged link s
 				, do
@@ -167,7 +166,7 @@ onAddSymlink threadname file filestatus dstatus transferqueue = go =<< Backend.l
 				)
 		go Nothing = do -- other symlink
 			link <- liftIO (readSymbolicLink file)
-			ensurestaged link =<< getDaemonStatus dstatus
+			ensurestaged link =<< liftIO (getDaemonStatus dstatus)
 
 		{- This is often called on symlinks that are already
 		 - staged correctly. A symlink may have been deleted

Assistant/Threads/WebApp.hs

@@ -115,7 +115,7 @@ statusDisplay = do
 	
 	current <- liftIO $ runThreadState (threadState webapp) $
 		M.toList . currentTransfers
-			<$> getDaemonStatus (daemonStatus webapp)
+			<$> liftIO (getDaemonStatus $ daemonStatus webapp)
 	queued <- liftIO $ getTransferQueue $ transferQueue webapp
 	let transfers = current ++ queued
 

Assistant/TransferQueue.hs

@@ -59,7 +59,7 @@ stubInfo f r = TransferInfo
 {- Adds transfers to queue for some of the known remotes. -}
 queueTransfers :: Schedule -> TransferQueue -> DaemonStatusHandle -> Key -> AssociatedFile -> Direction -> Annex ()
 queueTransfers schedule q daemonstatus k f direction = do
-	rs <- knownRemotes <$> getDaemonStatus daemonstatus
+	rs <- knownRemotes <$> liftIO (getDaemonStatus daemonstatus)
 	mapM_ go =<< sufficientremotes rs
 	where
 		sufficientremotes rs