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Assistant.hs

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+{- git-annex assistant daemon
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -
+ - Overview of threads and MVars, etc:
+ -
+ - Thread 1: parent
+ - 	The initial thread run, double forks to background, starts other
+ - 	threads, and then stops, waiting for them to terminate,
+ - 	or for a ctrl-c.
+ - Thread 2: inotify
+ - 	Notices new files, and calls handlers for events, queuing changes.
+ - Thread 3: inotify internal
+ - 	Used by haskell inotify library to ensure inotify event buffer is
+ - 	kept drained.
+ - Thread 4: inotify initial scan
+ -	A MVar lock is used to prevent other inotify handlers from running
+ -	until this is complete.
+ - Thread 5: committer
+ - 	Waits for changes to occur, and runs the git queue to update its
+ - 	index, then commits.
+ - Thread 6: status logger
+ - 	Wakes up periodically and records the daemon's status to disk.
+ -
+ - ThreadState: (MVar)
+ - 	The Annex state is stored here, which allows resuscitating the
+ - 	Annex monad in IO actions run by the inotify 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.
+ - ChangeChan: (STM TChan)
+ - 	Changes are indicated by writing to this channel. The committer
+ - 	reads from it.
+ -}
+
+module Assistant where
+
+import Common.Annex
+import Assistant.ThreadedMonad
+import Assistant.DaemonStatus
+import Assistant.Watcher
+import Assistant.Committer
+import qualified Utility.Daemon
+import Utility.LogFile
+
+import Control.Concurrent
+
+startDaemon :: Bool -> Annex ()
+startDaemon foreground
+	| foreground = do
+		showStart "watch" "."
+		go id
+	| otherwise = do
+		logfd <- liftIO . openLog =<< fromRepo gitAnnexLogFile
+		pidfile <- fromRepo gitAnnexPidFile
+		go $ Utility.Daemon.daemonize logfd (Just pidfile) False
+	where
+		go a = withThreadState $ \st -> liftIO $ a $ do
+			dstatus <- startDaemonStatus
+			changechan <- newChangeChan
+			-- The commit thread is started early, so that the user
+			-- can immediately begin adding files and having them
+			-- committed, even while the startup scan is taking
+			-- place.
+			_ <- forkIO $ commitThread st changechan
+			watchThread st dstatus changechan
+
+stopDaemon :: Annex ()
+stopDaemon = liftIO . Utility.Daemon.stopDaemon =<< fromRepo gitAnnexPidFile