the syncer now pushes out changes to remotes, in parallel

Note that, since this always pushes branch synced/master to the remote, it
assumes that master has already gotten all the commits that are on the
remote merged in. Otherwise, fast-forward prevention may prevent the push.

That's probably ok, because the next stage is to automatically detect
incoming pushes and merge.

Assistant/Syncer.hs

@@ -5,25 +5,63 @@
 
 module Assistant.Syncer where
 
+import Common.Annex
 import Assistant.Commits
 import Assistant.ThreadedMonad
 import qualified Command.Sync
 import Utility.ThreadScheduler
+import Utility.Parallel
+
+import Data.Time.Clock
+
+data FailedSync = FailedSync 
+	{ failedRemote :: Remote
+	, failedTimeStamp :: UTCTime
+	}
 
 {- This thread syncs git commits out to remotes. -}
 syncThread :: ThreadState -> CommitChan -> IO ()
-syncThread st commitchan = runEvery (Seconds 2) $ do
+syncThread st commitchan = do
+	remotes <- runThreadState st $ Command.Sync.syncRemotes []
+	runEveryWith (Seconds 2) [] $ \failedsyncs -> do
 		-- We already waited two seconds as a simple rate limiter.
 		-- Next, wait until at least one commit has been made
 		commits <- getCommits commitchan
 		-- Now see if now's a good time to sync.
-	if shouldSync commits
-		then syncToRemotes
-		else refillCommits commitchan commits
+		time <- getCurrentTime
+		if shouldSync time commits failedsyncs
+			then syncToRemotes time st remotes
+			else do
+				refillCommits commitchan commits
+				return failedsyncs
 
-{- Decide if now is a good time to sync commits to remotes. -}
-shouldSync :: [Commit] -> Bool
-shouldSync commits = not (null commits)
+{- Decide if now is a good time to sync to remotes.
+ -
+ - Current strategy: Immediately sync all commits. The commit machinery
+ - already determines batches of changes, so we can't easily determine
+ - batches better.
+ -
+ - TODO: FailedSyncs are only retried the next time there's a commit.
+ - Should retry them periodically, or when a remote that was not available
+ - becomes available.
+ -}
+shouldSync :: UTCTime -> [Commit] -> [FailedSync] -> Bool
+shouldSync _now commits _failedremotes
+	| not (null commits) = True
+	| otherwise = False
 
-syncToRemotes :: IO ()
-syncToRemotes = return () -- TOOD
+{- Updates the local sync branch, then pushes it to all remotes, in
+ - parallel.
+ -
+ - Avoids running possibly long-duration commands in the Annex monad, so
+ - as not to block other threads. -}
+syncToRemotes :: UTCTime -> ThreadState -> [Remote] -> IO [FailedSync]
+syncToRemotes now st remotes = do
+	(g, branch) <- runThreadState st $
+		(,) <$> fromRepo id <*> Command.Sync.currentBranch
+	Command.Sync.updateBranch (Command.Sync.syncBranch branch) g
+	map (`FailedSync` now) <$> inParallel (go g branch) remotes
+	where
+		go g branch remote =
+			ifM (Command.Sync.pushBranch remote branch g)
+				( exitSuccess, exitFailure)

Command/Sync.hs

@@ -31,7 +31,7 @@ def = [command "sync" (paramOptional (paramRepeating paramRemote))
 -- syncing involves several operations, any of which can independently fail
 seek :: CommandSeek
 seek rs = do
-	!branch <- fromMaybe nobranch <$> inRepo Git.Branch.current
+	branch <- currentBranch
 	remotes <- syncRemotes rs
 	return $ concat
 		[ [ commit ]
@@ -41,6 +41,11 @@ seek rs = do
 		, [ pushLocal branch ]
 		, [ pushRemote remote branch | remote <- remotes ]
 		]
+
+currentBranch :: Annex Git.Ref
+currentBranch = do
+	!branch <- fromMaybe nobranch <$> inRepo Git.Branch.current
+	return branch
 	where
 		nobranch = error "no branch is checked out"
 
@@ -90,7 +95,7 @@ mergeLocal branch = go =<< needmerge
 		syncbranch = syncBranch branch
 		needmerge = do
 			unlessM (inRepo $ Git.Ref.exists syncbranch) $
-				updateBranch syncbranch
+				inRepo $ updateBranch syncbranch
 			inRepo $ Git.Branch.changed branch syncbranch
 		go False = stop
 		go True = do
@@ -99,17 +104,17 @@ mergeLocal branch = go =<< needmerge
 
 pushLocal :: Git.Ref -> CommandStart
 pushLocal branch = do
-	updateBranch $ syncBranch branch
+	inRepo $ updateBranch $ syncBranch branch
 	stop
 
-updateBranch :: Git.Ref -> Annex ()
-updateBranch syncbranch = 
+updateBranch :: Git.Ref -> Git.Repo -> IO ()
+updateBranch syncbranch g = 
 	unlessM go $ error $ "failed to update " ++ show syncbranch
 	where
-		go = inRepo $ Git.Command.runBool "branch"
+		go = Git.Command.runBool "branch"
 			[ Param "-f"
 			, Param $ show $ Git.Ref.base syncbranch
-			]
+			] g
 
 pullRemote :: Remote -> Git.Ref -> CommandStart
 pullRemote remote branch = do
@@ -135,19 +140,27 @@ mergeRemote remote branch = all id <$> (mapM merge =<< tomerge)
 pushRemote :: Remote -> Git.Ref -> CommandStart
 pushRemote remote branch = go =<< needpush
 	where
-		needpush = anyM (newer remote) [syncbranch, Annex.Branch.name]
+		needpush = anyM (newer remote) [syncBranch branch, Annex.Branch.name]
 		go False = stop
 		go True = do
 			showStart "push" (Remote.name remote)
 			next $ next $ do
 				showOutput
-				inRepo $ Git.Command.runBool "push"
+				inRepo $ pushBranch remote branch
+
+pushBranch :: Remote -> Git.Ref -> Git.Repo -> IO Bool
+pushBranch remote branch g =
+	Git.Command.runBool "push"
 		[ Param (Remote.name remote)
 		, Param (show Annex.Branch.name)
 		, Param refspec
+		] g
+	where
+		refspec = concat 
+			[ show $ Git.Ref.base branch
+			,  ":"
+			, show $ Git.Ref.base $ syncBranch branch
 			]
-		refspec = show (Git.Ref.base branch) ++ ":" ++ show (Git.Ref.base syncbranch)
-		syncbranch = syncBranch branch
 
 mergeAnnex :: CommandStart
 mergeAnnex = do

Utility/Parallel.hs

@@ -0,0 +1,20 @@
+{- parallel processes
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.Parallel where
+
+import Common
+
+{- Runs an action in parallel with a set of values.
+ - Returns values that caused the action to fail. -}
+inParallel :: (v -> IO ()) -> [v] -> IO [v]
+inParallel a v = do
+	pids <- mapM (forkProcess . a) v
+	statuses <- mapM (getProcessStatus True False) pids
+	return $ map fst $ filter failed $ zip v statuses
+	where
+		failed (_, status) = status /= Just (Exited ExitSuccess)

Utility/ThreadScheduler.hs

@@ -24,6 +24,12 @@ runEvery n a = forever $ do
 	threadDelaySeconds n
 	a
 
+runEveryWith :: Seconds -> a -> (a -> IO a) -> IO ()
+runEveryWith n val a = do
+	threadDelaySeconds n
+	val' <- a val
+	runEveryWith n val' a
+
 threadDelaySeconds :: Seconds -> IO ()
 threadDelaySeconds (Seconds n) = unboundDelay (fromIntegral n * oneSecond)
 	where