git-annex/Assistant.hs

{- 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: Watcher
 - 	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 startup scanner
 - 	Scans the tree and registers inotify watches for each directory.
 -	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. Also queues Transfer events to send added
 - 	files to other remotes.
 - Thread 6: Pusher
 - 	Waits for commits to be made, and pushes updated branches to remotes,
 - 	in parallel. (Forks a process for each git push.)
 - Thread 7: PushRetryer
 - 	Runs every 30 minutes when there are failed pushes, and retries
 - 	them.
 - Thread 8: Merger
 - 	Waits for pushes to be received from remotes, and merges the
 - 	updated branches into the current branch.
 - 	(This uses inotify on .git/refs/heads, so there are additional
 - 	inotify threads associated with it, too.)
 - Thread 9: TransferWatcher
 - 	Watches for transfer information files being created and removed,
 - 	and maintains the DaemonStatus currentTransfers map.
 - 	(This uses inotify on .git/annex/transfer/, so there are
 - 	additional inotify threads associated with it, too.)
 - Thread 10: TransferPoller
 -	Polls to determine how much of each ongoing transfer is complete.
 - Thread 11: Transferrer
 - 	Waits for Transfers to be queued and does them.
 - Thread 12: StatusLogger
 - 	Wakes up periodically and records the daemon's status to disk.
 - Thread 13: SanityChecker
 - 	Wakes up periodically (rarely) and does sanity checks.
 - Thread 14: MountWatcher
 - 	Either uses dbus to watch for drive mount events, or, when
 - 	there's no dbus, polls to find newly mounted filesystems.
 - 	Once a filesystem that contains a remote is mounted, updates
 - 	state about that remote, pulls from it, and queues a push to it,
 - 	as well as an update, and queues it onto the
 - 	ConnectedRemoteChan
 - Thread 15: NetWatcher
 - 	Deals with network connection interruptions, which would cause
 - 	transfers to fail, and can be recovered from by waiting for a
 - 	network connection, and syncing with all network remotes.
 - 	Uses dbus to watch for network connections, or when dbus
 - 	cannot be used, assumes there's been one every 30 minutes.
 - Thread 16: TransferScanner
 - 	Does potentially expensive checks to find data that needs to be
 - 	transferred from or to remotes, and queues Transfers.
 - 	Uses the ScanRemotes map.a
 - Thread 17: PairListener
 - 	Listens for incoming pairing traffic, and takes action.
 - Thread 18: ConfigMonitor
 - 	Triggered by changes to the git-annex branch, checks for changed
 - 	config files, and reloads configs.
 - Thread 19: PushNotifier
 - 	Notifies other repositories of pushes, using out of band signaling.
 - Thread 20: WebApp
 - 	Spawns more threads as necessary to handle clients.
 - 	Displays the DaemonStatus.
 -
 - ThreadState: (MVar)
 - 	The Annex state is stored here, which allows resuscitating the
 - 	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: (STM TMVar)
 - 	The daemon's current status.
 - ChangeChan: (STM TChan)
 - 	Changes are indicated by writing to this channel. The committer
 - 	reads from it.
 - CommitChan: (STM TChan)
 - 	Commits are indicated by writing to this channel. The pusher reads
 - 	from it.
 - FailedPushMap (STM TMVar)
 - 	Failed pushes are indicated by writing to this TMVar. The push
 - 	retrier blocks until they're available.
 - TransferQueue (STM TChan)
 - 	Transfers to make are indicated by writing to this channel.
 - TransferSlots (QSemN)
 - 	Count of the number of currently available transfer slots.
 - 	Updated by the transfer watcher, this allows other threads
 - 	to block until a slot is available.
 - 	This MVar should only be manipulated from inside the Annex monad,
 - 	which ensures it's accessed only after the ThreadState MVar.
 - ScanRemotes (STM TMVar)
 - 	Remotes that have been disconnected, and should be scanned
 - 	are indicated by writing to this TMVar.
 - BranchChanged (STM SampleVar)
 - 	Changes to the git-annex branch are indicated by updating this
 - 	SampleVar.
 - PushNotifier (STM TChan)
 - 	After successful pushes, this SampleVar is updated.
 - UrlRenderer (MVar)
 - 	A Yesod route rendering function is stored here. This allows
 - 	things that need to render Yesod routes to block until the webapp
 - 	has started up and such rendering is possible.
 -}

{-# LANGUAGE CPP #-}

module Assistant where

import Assistant.Common
import Assistant.DaemonStatus
import Assistant.NamedThread
import Assistant.Types.ThreadedMonad
import Assistant.Threads.DaemonStatus
import Assistant.Threads.Watcher
import Assistant.Threads.Committer
import Assistant.Threads.Pusher
import Assistant.Threads.Merger
import Assistant.Threads.TransferWatcher
import Assistant.Threads.Transferrer
import Assistant.Threads.SanityChecker
import Assistant.Threads.MountWatcher
import Assistant.Threads.NetWatcher
import Assistant.Threads.TransferScanner
import Assistant.Threads.TransferPoller
import Assistant.Threads.ConfigMonitor
#ifdef WITH_XMPP
import Assistant.Threads.PushNotifier
#endif
#ifdef WITH_WEBAPP
import Assistant.WebApp
import Assistant.Threads.WebApp
#ifdef WITH_PAIRING
import Assistant.Threads.PairListener
#endif
#else
#warning Building without the webapp. You probably need to install Yesod..
#endif
import qualified Utility.Daemon
import Utility.LogFile
import Utility.ThreadScheduler

import Control.Concurrent

type NamedThread = IO () -> IO (String, IO ())

stopDaemon :: Annex ()
stopDaemon = liftIO . Utility.Daemon.stopDaemon =<< fromRepo gitAnnexPidFile

startDaemon :: Bool -> Bool -> Maybe (String -> FilePath -> IO ()) -> Annex ()
startDaemon assistant foreground webappwaiter
	| foreground = do
		showStart (if assistant then "assistant" else "watch") "."
		liftIO . Utility.Daemon.lockPidFile =<< fromRepo gitAnnexPidFile
		go id
	| otherwise = do
		logfd <- liftIO . openLog =<< fromRepo gitAnnexLogFile
		pidfile <- fromRepo gitAnnexPidFile
		go $ Utility.Daemon.daemonize logfd (Just pidfile) False
  where
	go d = startAssistant assistant d webappwaiter

startAssistant :: Bool -> (IO () -> IO ()) -> Maybe (String -> FilePath -> IO ()) -> Annex ()
startAssistant assistant daemonize webappwaiter = withThreadState $ \st -> do
	checkCanWatch
	dstatus <- startDaemonStatus
	liftIO $ daemonize $
		runAssistant go =<< newAssistantData st dstatus
  where
	go = do
		d <- getAssistant id
#ifdef WITH_WEBAPP
		urlrenderer <- liftIO newUrlRenderer
#endif
		mapM_ (startthread d)
			[ watch $ commitThread
#ifdef WITH_WEBAPP
			, assist $ webAppThread d urlrenderer False Nothing webappwaiter
#ifdef WITH_PAIRING
			, assist $ pairListenerThread urlrenderer
#endif
#endif
			, assist $ pushThread
			, assist $ pushRetryThread
			, assist $ mergeThread
			, assist $ transferWatcherThread
			, assist $ transferPollerThread
			, assist $ transfererThread
			, assist $ daemonStatusThread
			, assist $ sanityCheckerThread
			, assist $ mountWatcherThread
			, assist $ netWatcherThread
			, assist $ netWatcherFallbackThread
			, assist $ transferScannerThread
			, assist $ configMonitorThread
#ifdef WITH_XMPP
			, assist $ pushNotifierThread
#endif
			, watch $ watchThread
			]
		liftIO waitForTermination

	watch a = (True, a)
	assist a = (False, a)
	startthread d (watcher, t)
		| watcher || assistant = void $ liftIO $ forkIO $
			flip runAssistant d $
				runNamedThread t
		| otherwise = noop