add transfer watching thread

Worked the 1st try!

Assistant/Threads/TransferWatcher.hs

@@ -0,0 +1,78 @@
+{- git-annex assistant transfer watching thread
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Threads.TransferWatcher where
+
+import Common.Annex
+import Assistant.ThreadedMonad
+import Assistant.DaemonStatus
+import Logs.Transfer
+import Utility.DirWatcher
+import Utility.Types.DirWatcher
+
+import Data.Map as M
+
+{- This thread watches for changes to the gitAnnexTransferDir,
+ - and updates the DaemonStatus's map of ongoing transfers. -}
+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 a
+	let hooks = mkWatchHooks
+		{ addHook = hook onAdd
+		, delHook = hook onDel
+		, errHook = hook onErr
+		}
+	void $ watchDir dir (const False) hooks id
+
+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 -> Handler -> FilePath -> Maybe FileStatus -> IO ()
+runHandler st dstatus handler file filestatus = void $ do
+        either print (const noop) =<< tryIO go
+        where
+                go = handler st dstatus file filestatus
+
+{- Called when there's an error with inotify. -}
+onErr :: Handler
+onErr _ _ msg _ = error msg
+
+{- Called when a new transfer information file is written. 
+ -
+ - When another thread of the assistant writes a transfer info file,
+ - this will notice that too, but should skip it, because the thread
+ - will be managing the transfer itself, and will have stored a more
+ - complete TransferInfo than is stored in the file.
+ -}
+onAdd :: Handler
+onAdd st dstatus file _ = case parseTransferFile file of
+	Nothing -> noop
+	Just t -> do
+		minfo <- runThreadState st $ checkTransfer t
+		pid <- getProcessID
+		case minfo of
+			Nothing -> noop -- transfer already finished
+			Just info
+				| transferPid info == Just pid -> noop
+				| otherwise -> adjustTransfers st dstatus
+				(M.insertWith' const t info)
+
+{- Called when a transfer information file is removed. -}
+onDel :: Handler
+onDel st dstatus file _ = case parseTransferFile file of
+	Nothing -> noop
+	Just t -> adjustTransfers st dstatus (M.delete t)
+
+adjustTransfers :: ThreadState -> DaemonStatusHandle -> (M.Map Transfer TransferInfo -> M.Map Transfer TransferInfo) -> IO ()
+adjustTransfers st dstatus a = runThreadState st $ modifyDaemonStatus dstatus $
+	\s -> s { currentTransfers = a (currentTransfers s) }