run file transfers in threads, not processes

This should fix OSX/BSD issues with not noticing transfer information
files with kqueue. Now that threads are used, the thread can manage the
transfer slot allocation and deallocation by itself; much cleaner.

Assistant.hs

@@ -123,7 +123,7 @@ startDaemon assistant foreground
 				, pushThread st dstatus commitchan pushmap
 				, pushRetryThread st pushmap
 				, mergeThread st
-				, transferWatcherThread st dstatus transferslots
+				, transferWatcherThread st dstatus
 				, transfererThread st dstatus transferqueue transferslots
 				, daemonStatusThread st dstatus
 				, sanityCheckerThread st dstatus transferqueue changechan

Assistant/ThreadedMonad.hs

@@ -37,14 +37,13 @@ withThreadState a = do
 runThreadState :: ThreadState -> Annex a -> IO a
 runThreadState mvar a = modifyMVar mvar $ \state -> swap <$> Annex.run state a
 
-{- Runs an Annex action in a separate thread, using a copy of the state
- - from the MVar.
+{- Runs an Annex action, using a copy of the state from the MVar.
  -
  - It's up to the action to perform any necessary shutdown tasks in order
  - for state to not be lost. And it's up to the caller to resynchronise
  - with any changes the action makes to eg, the git-annex branch.
  -}
-unsafeForkIOThreadState :: ThreadState -> Annex a -> IO ThreadId
-unsafeForkIOThreadState mvar a = do
+unsafeRunThreadState :: ThreadState -> Annex a -> IO ()
+unsafeRunThreadState mvar a = do
 	state <- readMVar mvar
-	forkIO $ void $ Annex.eval state a
+	void $ Annex.eval state a

Assistant/Threads/TransferWatcher.hs

@@ -10,23 +10,20 @@ module Assistant.Threads.TransferWatcher where
 import Common.Annex
 import Assistant.ThreadedMonad
 import Assistant.DaemonStatus
-import Assistant.TransferSlots
 import Logs.Transfer
 import Utility.DirWatcher
 import Utility.Types.DirWatcher
-import Annex.BranchState
 
 import Data.Map as M
-import System.Posix.Process
 
 {- This thread watches for changes to the gitAnnexTransferDir,
  - and updates the DaemonStatus's map of ongoing transfers. -}
-transferWatcherThread :: ThreadState -> DaemonStatusHandle -> TransferSlots -> IO ()
-transferWatcherThread st dstatus transferslots = do
+transferWatcherThread :: ThreadState -> DaemonStatusHandle -> IO ()
+transferWatcherThread st dstatus = do
 	g <- runThreadState st $ fromRepo id
 	let dir = gitAnnexTransferDir g
 	createDirectoryIfMissing True dir
-	let hook a = Just $ runHandler st dstatus transferslots a
+	let hook a = Just $ runHandler st dstatus a
 	let hooks = mkWatchHooks
 		{ addHook = hook onAdd
 		, delHook = hook onDel
@@ -34,51 +31,36 @@ transferWatcherThread st dstatus transferslots = do
 		}
 	void $ watchDir dir (const False) hooks id
 
-type Handler = ThreadState -> DaemonStatusHandle -> TransferSlots -> FilePath -> Maybe FileStatus -> IO ()
+type Handler = ThreadState -> DaemonStatusHandle -> FilePath -> Maybe FileStatus -> IO ()
 
 {- Runs an action handler.
  -
  - Exceptions are ignored, otherwise a whole thread could be crashed.
  -}
-runHandler :: ThreadState -> DaemonStatusHandle -> TransferSlots -> Handler -> FilePath -> Maybe FileStatus -> IO ()
-runHandler st dstatus transferslots handler file filestatus = void $ do
+runHandler :: ThreadState -> DaemonStatusHandle -> Handler -> FilePath -> Maybe FileStatus -> IO ()
+runHandler st dstatus handler file filestatus = void $ do
         either print (const noop) =<< tryIO go
         where
-                go = handler st dstatus transferslots file filestatus
+                go = handler st dstatus file filestatus
 
 {- Called when there's an error with inotify. -}
 onErr :: Handler
-onErr _ _ _ msg _ = error msg
+onErr _ _ msg _ = error msg
 
 {- Called when a new transfer information file is written. -}
 onAdd :: Handler
-onAdd st dstatus _ file _ = case parseTransferFile file of
+onAdd st dstatus file _ = case parseTransferFile file of
 	Nothing -> noop
 	Just t -> runThreadState st $ go t =<< checkTransfer t
 	where
 		go _ Nothing = noop -- transfer already finished
 		go t (Just info) = adjustTransfers dstatus $
 			M.insertWith' merge t info
-		-- preseve shouldWait flag, which is not written to disk
-		merge new old = new { shouldWait = shouldWait old }
+		-- preseve transferTid, which is not written to disk
+		merge new old = new { transferTid = transferTid old }
 
-{- Called when a transfer information file is removed.
- -
- - When the transfer process is a child of this process, wait on it
- - to avoid zombies.
- -}
+{- Called when a transfer information file is removed. -}
 onDel :: Handler
-onDel st dstatus transferslots file _ = case parseTransferFile file of
+onDel st dstatus file _ = case parseTransferFile file of
 	Nothing -> noop
-	Just t -> maybe noop waitchild
-		=<< runThreadState st (removeTransfer dstatus t)
-	where
-		waitchild info
-			| shouldWait info = case transferPid info of
-				Nothing -> noop
-				Just pid -> do
-					void $ tryIO $ 
-						getProcessStatus True False pid
-					runThreadState st invalidateCache
-					transferComplete transferslots
-			| otherwise = noop	
+	Just t -> void $ runThreadState st $ removeTransfer dstatus t

Assistant/Threads/Transferrer.hs

@@ -74,9 +74,8 @@ runTransfer st dstatus slots t info = case (transferRemote info, associatedFile
 	(Nothing, _) -> noop
 	(_, Nothing) -> noop
 	(Just remote, Just file) -> do
-		tid <- inTransferSlot slots $
-			unsafeForkIOThreadState st $
-				transferprocess remote file
+		tid <- inTransferSlot slots st $
+			transferprocess remote file
 		now <- getCurrentTime
 		runThreadState st $ adjustTransfers dstatus $
 			M.insertWith' const t info

Assistant/TransferQueue.hs

@@ -28,7 +28,6 @@ stubInfo f = TransferInfo
 	, transferRemote = Nothing
 	, bytesComplete = Nothing
 	, associatedFile = f
-	, shouldWait = False
 	}
 
 {- Adds pending transfers to the end of the queue for some of the known

Assistant/TransferSlots.hs

@@ -10,6 +10,9 @@ module Assistant.TransferSlots where
 import Control.Exception
 import Control.Concurrent
 
+import Common.Annex
+import Assistant.ThreadedMonad
+
 type TransferSlots = QSemN
 
 {- Number of concurrent transfers allowed to be run from the assistant.
@@ -24,16 +27,13 @@ newTransferSlots :: IO TransferSlots
 newTransferSlots = newQSemN numSlots
 
 {- Waits until a transfer slot becomes available, and runs a transfer
- - action in the slot. If the action throws an exception, its slot is
- - freed here, otherwise it should be freed by the TransferWatcher when
- - the transfer is complete.
- -}
-inTransferSlot :: TransferSlots -> IO a -> IO a
-inTransferSlot s a = bracketOnError start abort run
+ - action in the slot, in its own thread. -}
+inTransferSlot :: TransferSlots -> ThreadState -> Annex a -> IO ThreadId
+inTransferSlot s st a = forkIO $ bracket_ start done run
 	where
 		start = waitQSemN s 1
-		abort = const $ transferComplete s
-		run = const a
+		done = transferComplete s
+		run = unsafeRunThreadState st a
 
 {- Call when a transfer is complete. -}
 transferComplete :: TransferSlots -> IO ()

Logs/Transfer.hs

@@ -43,7 +43,6 @@ data TransferInfo = TransferInfo
 	, transferRemote :: Maybe Remote
 	, bytesComplete :: Maybe Integer
 	, associatedFile :: Maybe FilePath
-	, shouldWait :: Bool
 	}
 	deriving (Show, Eq, Ord)
 
@@ -87,7 +86,6 @@ transfer t file a = do
 		<*> pure Nothing -- not 0; transfer may be resuming
 		<*> pure Nothing
 		<*> pure file
-		<*> pure False
 	bracketIO (prep tfile mode info) (cleanup tfile) a
 	where
 		prep tfile mode info = do
@@ -180,7 +178,6 @@ readTransferInfo pid s =
 			<*> pure Nothing
 			<*> pure Nothing
 			<*> pure (if null filename then Nothing else Just filename)
-			<*> pure False
 		_ -> Nothing
 	where
 		(bits, filebits) = splitAt 1 $ lines s