add exporter thread to assistant

This is similar to the pusher thread, but a separate thread because git
pushes can be done in parallel with exports, and updating a big export
should not prevent other git pushes going out in the meantime.

The exportThread only runs at most every 30 seconds, since updating an
export is more expensive than pushing. This may need to be tuned.

Added a separate channel for export commits; the committer records a
commit in that channel.

Also, reconnectRemotes records a dummy commit, to make the exporter
thread wake up and make sure all exports are up-to-date. So,
connecting a drive with a directory special remote export will
immediately update it, and getting online will automatically
update S3 and WebDAV exports.

The transfer queue is not involved in exports. Instead, failed
exports are retried much like failed pushes.

This commit was sponsored by Ewen McNeill.

13 files changed, 124 insertions, 22 deletions

diff --git a/Assistant.hs b/Assistant.hs
index ea9967610..81aa036f6 100644
--- a/Assistant.hs
+++ b/Assistant.hs
@@ -18,6 +18,7 @@ import Assistant.Threads.DaemonStatus
 import Assistant.Threads.Watcher
 import Assistant.Threads.Committer
 import Assistant.Threads.Pusher
+import Assistant.Threads.Exporter
 import Assistant.Threads.Merger
 import Assistant.Threads.TransferWatcher
 import Assistant.Threads.Transferrer
@@ -152,6 +153,8 @@ startDaemon assistant foreground startdelay cannotrun listenhost startbrowser =
 #endif
 				, assist pushThread
 				, assist pushRetryThread
+				, assist exportThread
+				, assist exportRetryThread
 				, assist mergeThread
 				, assist transferWatcherThread
 				, assist transferPollerThread
diff --git a/Assistant/Commits.hs b/Assistant/Commits.hs
index c82f8f4c7..255648c94 100644
--- a/Assistant/Commits.hs
+++ b/Assistant/Commits.hs
@@ -21,3 +21,12 @@ getCommits = (atomically . getTList) <<~ commitChan
 {- Records a commit in the channel. -}
 recordCommit :: Assistant ()
 recordCommit = (atomically . flip consTList Commit) <<~ commitChan
+
+{- Gets all unhandled export commits.
+ - Blocks until at least one export commit is made. -}
+getExportCommits :: Assistant [Commit]
+getExportCommits = (atomically . getTList) <<~ exportCommitChan
+
+{- Records an export commit in the channel. -}
+recordExportCommit :: Assistant ()
+recordExportCommit = (atomically . flip consTList Commit) <<~ exportCommitChan
diff --git a/Assistant/Monad.hs b/Assistant/Monad.hs
index e52983915..403ee16a8 100644
--- a/Assistant/Monad.hs
+++ b/Assistant/Monad.hs
@@ -62,7 +62,9 @@ data AssistantData = AssistantData
 	, transferSlots :: TransferSlots
 	, transferrerPool :: TransferrerPool
 	, failedPushMap :: FailedPushMap
+	, failedExportMap :: FailedPushMap
 	, commitChan :: CommitChan
+	, exportCommitChan :: CommitChan
 	, changePool :: ChangePool
 	, repoProblemChan :: RepoProblemChan
 	, branchChangeHandle :: BranchChangeHandle
@@ -80,6 +82,8 @@ newAssistantData st dstatus = AssistantData
 	<*> newTransferSlots
 	<*> newTransferrerPool (checkNetworkConnections dstatus)
 	<*> newFailedPushMap
+	<*> newFailedPushMap
+	<*> newCommitChan
 	<*> newCommitChan
 	<*> newChangePool
 	<*> newRepoProblemChan
diff --git a/Assistant/Pushes.hs b/Assistant/Pushes.hs
index 7b4de450f..61891ea28 100644
--- a/Assistant/Pushes.hs
+++ b/Assistant/Pushes.hs
@@ -17,24 +17,21 @@ import qualified Data.Map as M
 {- Blocks until there are failed pushes.
  - Returns Remotes whose pushes failed a given time duration or more ago.
  - (This may be an empty list.) -}
-getFailedPushesBefore :: NominalDiffTime -> Assistant [Remote]
-getFailedPushesBefore duration = do
-	v <- getAssistant failedPushMap
-	liftIO $ do
-		m <- atomically $ readTMVar v
-		now <- getCurrentTime
-		return $ M.keys $ M.filter (not . toorecent now) m
+getFailedPushesBefore :: NominalDiffTime -> FailedPushMap -> Assistant [Remote]
+getFailedPushesBefore duration v = liftIO $ do
+	m <- atomically $ readTMVar v
+	now <- getCurrentTime
+	return $ M.keys $ M.filter (not . toorecent now) m
   where
 	toorecent now time = now `diffUTCTime` time < duration
 
 {- Modifies the map. -}
-changeFailedPushMap :: (PushMap -> PushMap) -> Assistant ()
-changeFailedPushMap a = do
-	v <- getAssistant failedPushMap
-	liftIO $ atomically $ store v . a . fromMaybe M.empty =<< tryTakeTMVar v
+changeFailedPushMap :: FailedPushMap -> (PushMap -> PushMap) -> Assistant ()
+changeFailedPushMap v f = liftIO $ atomically $
+	store . f . fromMaybe M.empty =<< tryTakeTMVar v
   where
 	{- tryTakeTMVar empties the TMVar; refill it only if
 	 - the modified map is not itself empty -}
-	store v m
+	store m
 		| m == M.empty = noop
 		| otherwise = putTMVar v $! m
diff --git a/Assistant/Sync.hs b/Assistant/Sync.hs
index aba90f64c..c6460e9ed 100644
--- a/Assistant/Sync.hs
+++ b/Assistant/Sync.hs
@@ -33,6 +33,7 @@ import Assistant.Threads.Watcher (watchThread, WatcherControl(..))
 import Assistant.TransferSlots
 import Assistant.TransferQueue
 import Assistant.RepoProblem
+import Assistant.Commits
 import Types.Transfer
 
 import Data.Time.Clock
@@ -48,10 +49,10 @@ import Control.Concurrent
  - it's sufficient to requeue failed transfers.
  -
  - Also handles signaling any connectRemoteNotifiers, after the syncing is
- - done.
+ - done, and records an export commit to make any exports be updated.
  -}
 reconnectRemotes :: [Remote] -> Assistant ()
-reconnectRemotes [] = noop
+reconnectRemotes [] = recordExportCommit
 reconnectRemotes rs = void $ do
 	rs' <- liftIO $ filterM (Remote.checkAvailable True) rs
 	unless (null rs') $ do
@@ -60,6 +61,7 @@ reconnectRemotes rs = void $ do
 			whenM (liftIO $ Remote.checkAvailable False r) $
 				repoHasProblem (Remote.uuid r) (syncRemote r)
 		mapM_ signal $ filter (`notElem` failedrs) rs'
+	recordExportCommit
   where
 	gitremotes = filter (notspecialremote . Remote.repo) rs
 	(_xmppremotes, nonxmppremotes) = partition Remote.isXMPPRemote rs
@@ -143,9 +145,11 @@ pushToRemotes' now remotes = do
 				then retry currbranch g u failed
 				else fallback branch g u failed
 
-	updatemap succeeded failed = changeFailedPushMap $ \m ->
-		M.union (makemap failed) $
-			M.difference m (makemap succeeded)
+	updatemap succeeded failed = do
+		v <- getAssistant failedPushMap 
+		changeFailedPushMap v $ \m ->
+			M.union (makemap failed) $
+				M.difference m (makemap succeeded)
 	makemap l = M.fromList $ zip l (repeat now)
 
 	retry currbranch g u rs = do
diff --git a/Assistant/Threads/Committer.hs b/Assistant/Threads/Committer.hs
index 3680349be..aa57d26a8 100644
--- a/Assistant/Threads/Committer.hs
+++ b/Assistant/Threads/Committer.hs
@@ -67,6 +67,7 @@ commitThread = namedThread "Committer" $ do
 				void $ alertWhile commitAlert $
 					liftAnnex $ commitStaged msg
 				recordCommit
+				recordExportCommit
 				let numchanges = length readychanges
 				mapM_ checkChangeContent readychanges
 				return numchanges
diff --git a/Assistant/Threads/Exporter.hs b/Assistant/Threads/Exporter.hs
new file mode 100644
index 000000000..747e919da
--- /dev/null
+++ b/Assistant/Threads/Exporter.hs
@@ -0,0 +1,78 @@
+{- git-annex assistant export updating thread
+ -
+ - Copyright 2017 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Threads.Exporter where
+
+import Assistant.Common
+import Assistant.Commits
+import Assistant.Pushes
+import Assistant.DaemonStatus
+import Annex.Concurrent
+import Utility.ThreadScheduler
+import qualified Annex
+import qualified Remote
+import qualified Types.Remote as Remote
+import qualified Command.Sync
+
+import Control.Concurrent.Async
+import Data.Time.Clock
+import qualified Data.Map as M
+
+{- This thread retries exports that failed before. -}
+exportRetryThread :: NamedThread
+exportRetryThread = namedThread "ExportRetrier" $ runEvery (Seconds halfhour) <~> do
+	-- We already waited half an hour, now wait until there are failed
+	-- exports to retry.
+	toexport <- getFailedPushesBefore (fromIntegral halfhour) 
+		=<< getAssistant failedExportMap
+	unless (null toexport) $ do
+		debug ["retrying", show (length toexport), "failed exports"]
+		void $ exportToRemotes toexport
+  where
+	halfhour = 1800
+
+{- This thread updates exports soon after git commits are made. -}
+exportThread :: NamedThread
+exportThread = namedThread "Exporter" $ runEvery (Seconds 30) <~> do
+	-- We already waited two seconds as a simple rate limiter.
+	-- Next, wait until at least one commit has been made
+	void getExportCommits
+	-- Now see if now's a good time to push.
+	void $ exportToRemotes =<< exportTargets
+
+{- We want to avoid exporting to remotes that are marked readonly.
+ -
+ - Also, avoid exporting to local remotes we can easily tell are not available,
+ - to avoid ugly messages when a removable drive is not attached.
+ -}
+exportTargets :: Assistant [Remote]
+exportTargets = liftIO . filterM (Remote.checkAvailable True)
+	=<< candidates <$> getDaemonStatus
+  where
+	candidates = filter (not . Remote.readonly) . exportRemotes
+
+exportToRemotes :: [Remote] -> Assistant ()
+exportToRemotes rs = do
+	-- This is a long-duration action which runs in the Annex monad,
+	-- so don't just liftAnnex to run it; fork the Annex state.
+	runner <- liftAnnex $ forkState $
+		forM rs $ \r -> do
+			Annex.changeState $ \st -> st { Annex.errcounter = 0 }
+			start <- liftIO getCurrentTime
+			void $ Command.Sync.seekExportContent rs
+			-- Look at command error counter to see if the export
+			-- didn't work.
+			failed <- (> 0) <$> Annex.getState Annex.errcounter
+			Annex.changeState $ \st -> st { Annex.errcounter = 0 }
+			return $ if failed
+				then Just (r, start)
+				else Nothing
+	failed <- catMaybes
+		<$> (liftAnnex =<< liftIO . wait =<< liftIO (async runner))
+	unless (null failed) $ do
+		v <- getAssistant failedExportMap
+		changeFailedPushMap v $ M.union $ M.fromList failed
diff --git a/Assistant/Threads/Pusher.hs b/Assistant/Threads/Pusher.hs
index 5b4055885..82bd39d89 100644
--- a/Assistant/Threads/Pusher.hs
+++ b/Assistant/Threads/Pusher.hs
@@ -22,6 +22,7 @@ pushRetryThread = namedThread "PushRetrier" $ runEvery (Seconds halfhour) <~> do
 	-- We already waited half an hour, now wait until there are failed
 	-- pushes to retry.
 	topush <- getFailedPushesBefore (fromIntegral halfhour)
+		=<< getAssistant failedPushMap
 	unless (null topush) $ do
 		debug ["retrying", show (length topush), "failed pushes"]
 		void $ pushToRemotes topush
diff --git a/Assistant/Threads/TransferScanner.hs b/Assistant/Threads/TransferScanner.hs
index fd77b88d2..e76c0b4fb 100644
--- a/Assistant/Threads/TransferScanner.hs
+++ b/Assistant/Threads/TransferScanner.hs
@@ -59,8 +59,9 @@ transferScannerThread urlrenderer = namedThread "TransferScanner" $ do
 			(s { transferScanRunning = b }, s)
 		liftIO $ sendNotification $ transferNotifier ds
 		
-	{- All git remotes are synced, and all available remotes
-	 - are scanned in full on startup, for multiple reasons, including:
+	{- All git remotes are synced, all exports are updated,
+	 - and all available remotes are scanned in full on startup,
+	 - for multiple reasons, including:
 	 -
 	 - * This may be the first run, and there may be remotes
 	 -   already in place, that need to be synced.
diff --git a/CHANGELOG b/CHANGELOG
index 0e86e773c..fb9836c1d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,7 @@ git-annex (6.20170819) UNRELEASED; urgency=medium
     for use by git-annex export.
   * Implemented export to directory, S3, and webdav special remotes.
   * External special remote protocol extended to support export.
+  * sync, assistant: Update exports.
   * Support building with feed-1.0, while still supporting older versions.
   * init: Display an additional message when it detects a filesystem that
     allows writing to files whose write bit is not set.
diff --git a/Command/Sync.hs b/Command/Sync.hs
index 3a838c8a9..44948ea74 100644
--- a/Command/Sync.hs
+++ b/Command/Sync.hs
@@ -21,6 +21,7 @@ module Command.Sync (
 	updateBranch,
 	syncBranch,
 	updateSyncBranch,
+	seekExportContent,
 ) where
 
 import Command
@@ -652,7 +653,10 @@ syncFile ebloom rs af k = do
 
 {- When a remote has an export-tracking branch, change the export to
  - follow the current content of the branch. Otherwise, transfer any files
- - that were part of an export but are not in the remote yet. -}
+ - that were part of an export but are not in the remote yet.
+ - 
+ - Returns True if any file transfers were made.
+ -}
 seekExportContent :: [Remote] -> Annex Bool
 seekExportContent rs = or <$> forM rs go
   where
diff --git a/doc/todo/export.mdwn b/doc/todo/export.mdwn
index 7500de097..c33078668 100644
--- a/doc/todo/export.mdwn
+++ b/doc/todo/export.mdwn
@@ -17,8 +17,6 @@ there need to be a new interface in supported remotes?
 
 Work is in progress. Todo list:
 
-* Make assistant update tracking exports.
-
 * Support configuring export in the assistant
   (when eg setting up a S3 special remote).
 
diff --git a/git-annex.cabal b/git-annex.cabal
index e8c3d2373..8c7ff718f 100644
--- a/git-annex.cabal
+++ b/git-annex.cabal
@@ -580,6 +580,7 @@ Executable git-annex
     Assistant.Threads.ConfigMonitor
     Assistant.Threads.Cronner
     Assistant.Threads.DaemonStatus
+    Assistant.Threads.Exporter
     Assistant.Threads.Glacier
     Assistant.Threads.Merger
     Assistant.Threads.MountWatcher