add a push retry thread

Assistant.hs

@@ -25,14 +25,17 @@
  - 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: merger
+ - Thread 7: push retryer
+ - 	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 8: status logger
+ - Thread 9: status logger
  - 	Wakes up periodically and records the daemon's status to disk.
- - Thread 9: sanity checker
+ - Thread 10: sanity checker
  - 	Wakes up periodically (rarely) and does sanity checks.
  -
  - ThreadState: (MVar)
@@ -59,6 +62,7 @@ import Assistant.ThreadedMonad
 import Assistant.DaemonStatus
 import Assistant.Changes
 import Assistant.Commits
+import Assistant.Pushes
 import Assistant.Threads.Watcher
 import Assistant.Threads.Committer
 import Assistant.Threads.Pusher
@@ -85,8 +89,10 @@ startDaemon assistant foreground
 			liftIO $ a $ do
 				changechan <- newChangeChan
 				commitchan <- newCommitChan
+				pushchan <- newFailedPushChan
 				_ <- forkIO $ commitThread st changechan commitchan
-				_ <- forkIO $ pushThread st commitchan
+				_ <- forkIO $ pushThread st commitchan pushchan
+				_ <- forkIO $ pushRetryThread st pushchan
 				_ <- forkIO $ mergeThread st
 				_ <- forkIO $ daemonStatusThread st dstatus
 				_ <- forkIO $ sanityCheckerThread st dstatus changechan

Assistant/Pushes.hs

@@ -0,0 +1,36 @@
+{- git-annex assistant push tracking
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Pushes where
+
+import Common.Annex
+import Utility.TSet
+
+import Data.Time.Clock
+
+type FailedPushChan = TSet FailedPush
+
+data FailedPush = FailedPush
+        { failedRemote :: Remote
+        , failedTimeStamp :: UTCTime
+        }
+
+newFailedPushChan :: IO FailedPushChan
+newFailedPushChan = newTSet
+
+{- Gets all failed pushes. Blocks until there is at least one failed push. -}
+getFailedPushes :: FailedPushChan -> IO [FailedPush]
+getFailedPushes = getTSet
+
+{- Puts failed pushes back into the channel.
+ - Note: Original order is not preserved. -}
+refillFailedPushes :: FailedPushChan -> [FailedPush] -> IO ()
+refillFailedPushes = putTSet
+
+{- Records a failed push in the channel. -}
+recordFailedPush :: FailedPushChan -> FailedPush -> IO ()
+recordFailedPush = putTSet1

Assistant/Threads/Pusher.hs

@@ -1,4 +1,4 @@
-{- git-annex assistant git pushing thread
+{- git-annex assistant git pushing threads
  -
  - Copyright 2012 Joey Hess <joey@kitenet.net>
  -
@@ -9,6 +9,7 @@ module Assistant.Threads.Pusher where
 
 import Common.Annex
 import Assistant.Commits
+import Assistant.Pushes
 import Assistant.ThreadedMonad
 import qualified Command.Sync
 import Utility.ThreadScheduler
@@ -16,39 +17,45 @@ import Utility.Parallel
 
 import Data.Time.Clock
 
-data FailedPush = FailedPush 
-	{ failedRemote :: Remote
-	, failedTimeStamp :: UTCTime
-	}
+{- This thread retries pushes that failed before. -}
+pushRetryThread :: ThreadState -> FailedPushChan -> IO ()
+pushRetryThread st pushchan = runEvery (Seconds halfhour) $ do
+	-- We already waited half an hour, now wait until there are failed
+	-- pushes to retry.
+	pushes <- getFailedPushes pushchan
+	-- Check times, to avoid repushing a push that's too new.
+	now <- getCurrentTime
+	let (newpushes, oldpushes) = partition (toorecent now . failedTimeStamp) pushes
+	unless (null newpushes) $
+		refillFailedPushes pushchan newpushes
+	unless (null oldpushes) $
+		pushToRemotes now st pushchan $ map failedRemote oldpushes
+	where
+		halfhour = 1800
+		toorecent now time = now `diffUTCTime` time < fromIntegral halfhour
 
-{- This thread pushes git commits out to remotes. -}
-pushThread :: ThreadState -> CommitChan -> IO ()
-pushThread st commitchan = do
+{- This thread pushes git commits out to remotes soon after they are made. -}
+pushThread :: ThreadState -> CommitChan -> FailedPushChan -> IO ()
+pushThread st commitchan pushchan = do
 	remotes <- runThreadState st $ Command.Sync.syncRemotes []
-	runEveryWith (Seconds 2) [] $ \failedpushes -> do
+	runEvery (Seconds 2) $ 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 push.
-		time <- getCurrentTime
-		if shouldPush time commits failedpushes
-			then pushToRemotes time st remotes
-			else do
-				refillCommits commitchan commits
-				return failedpushes
+		now <- getCurrentTime
+		if shouldPush now commits
+			then pushToRemotes now st pushchan remotes
+			else refillCommits commitchan commits
 
 {- Decide if now is a good time to push to remotes.
  -
  - Current strategy: Immediately push all commits. The commit machinery
  - already determines batches of changes, so we can't easily determine
  - batches better.
- -
- - TODO: FailedPushs are only retried the next time there's a commit.
- - Should retry them periodically, or when a remote that was not available
- - becomes available.
  -}
-shouldPush :: UTCTime -> [Commit] -> [FailedPush] -> Bool
-shouldPush _now commits _failedremotes
+shouldPush :: UTCTime -> [Commit] -> Bool
+shouldPush _now commits
 	| not (null commits) = True
 	| otherwise = False
 
@@ -57,12 +64,14 @@ shouldPush _now commits _failedremotes
  -
  - Avoids running possibly long-duration commands in the Annex monad, so
  - as not to block other threads. -}
-pushToRemotes :: UTCTime -> ThreadState -> [Remote] -> IO [FailedPush]
-pushToRemotes now st remotes = do
+pushToRemotes :: UTCTime -> ThreadState -> FailedPushChan -> [Remote] -> IO ()
+pushToRemotes now st pushchan remotes = do
 	(g, branch) <- runThreadState st $
 		(,) <$> fromRepo id <*> Command.Sync.currentBranch
 	Command.Sync.updateBranch (Command.Sync.syncBranch branch) g
-	map (`FailedPush` now) <$> inParallel (push g branch) remotes
+	failed <- map (`FailedPush` now) <$> inParallel (push g branch) remotes
+	unless (null failed) $
+		refillFailedPushes pushchan failed
 	where
 		push g branch remote =
 			ifM (Command.Sync.pushBranch remote branch g)

Utility/ThreadScheduler.hs

@@ -24,12 +24,6 @@ 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

doc/design/assistant/syncing.mdwn

@@ -13,8 +13,9 @@ all the other git clones, at both the git level and the key/value level.
    [The watching can be done with the existing inotify code! This avoids needing
    any special mechanism to notify a remote that it's been synced to.]  
    **done**
-1. Periodically retry pushes that failed. Also, detect if a push failed
-   due to not being up-to-date, pull, and repush.
+1. Periodically retry pushes that failed.  **done** (every half an hour)
+1. Also, detect if a push failed due to not being up-to-date, pull,
+   and repush.
 2. Use a git merge driver that adds both conflicting files,
    so conflicts never break a sync.
 3. Investigate the XMPP approach like dvcs-autosync does, or other ways of