send notifications when the TransferQueue is changed

The fun part was making it move things from TransferQueue to currentTransfers
entirely atomically. Which will avoid inconsistent display if the WebApp
renders the current status at just the wrong time. STM to the rescue!

Assistant.hs

@@ -153,7 +153,7 @@ startDaemon assistant foreground webappwaiter
 				, daemonStatusThread st dstatus
 				, sanityCheckerThread st dstatus transferqueue changechan
 				, mountWatcherThread st dstatus scanremotes
-				, transferScannerThread st scanremotes transferqueue
+				, transferScannerThread st dstatus scanremotes transferqueue
 #ifdef WITH_WEBAPP
 				, webAppThread st dstatus transferqueue webappwaiter
 #endif

Assistant/DaemonStatus.hs

@@ -36,6 +36,7 @@ data DaemonStatus = DaemonStatus
 	-- Ordered list of remotes to talk to.
 	, knownRemotes :: [Remote]
 	-- Clients can use this to wait on changes to the DaemonStatus
+	-- and other related things like the TransferQueue.
 	, notificationBroadcaster :: NotificationBroadcaster
 	}
 
@@ -72,6 +73,12 @@ modifyDaemonStatus handle a = do
 	sendNotification nb
 	return b
 
+{- Can be used to send a notification that the daemon status, or other
+ - associated thing, like the TransferQueue, has changed. -}
+notifyDaemonStatusChange :: DaemonStatusHandle -> IO ()
+notifyDaemonStatusChange handle = sendNotification
+	=<< notificationBroadcaster <$> atomically (readTMVar handle)
+
 {- Updates the cached ordered list of remotes from the list in Annex
  - state. -}
 updateKnownRemotes :: DaemonStatusHandle -> Annex ()
@@ -164,7 +171,16 @@ afterLastDaemonRun timestamp status = maybe False (< t) (lastRunning status)
 tenMinutes :: Int
 tenMinutes = 10 * 60
 
-{- Mutates the transfer map. -}
+{- Mutates the transfer map. Runs in STM so that the transfer map can
+ - be modified in the same transaction that modifies the transfer queue.
+ - Note that this does not send a notification of the change; that's left
+ - to the caller. -}
+adjustTransfersSTM :: DaemonStatusHandle -> (TransferMap -> TransferMap) -> STM ()
+adjustTransfersSTM dstatus a = do
+	s <- takeTMVar dstatus
+	putTMVar dstatus $ s { currentTransfers = a (currentTransfers s) }
+
+{- Variant that does send notifications. -}
 adjustTransfers :: DaemonStatusHandle -> (TransferMap -> TransferMap) -> IO ()
 adjustTransfers dstatus a = modifyDaemonStatus_ dstatus $
 	\s -> s { currentTransfers = a (currentTransfers s) }

Assistant/Threads/TransferScanner.hs

@@ -11,6 +11,7 @@ import Assistant.Common
 import Assistant.ScanRemotes
 import Assistant.TransferQueue
 import Assistant.ThreadedMonad
+import Assistant.DaemonStatus
 import Logs.Transfer
 import Logs.Location
 import qualified Remote
@@ -25,20 +26,20 @@ thisThread = "TransferScanner"
 {- This thread waits until a remote needs to be scanned, to find transfers
  - that need to be made, to keep data in sync.
  -}
-transferScannerThread :: ThreadState -> ScanRemoteMap -> TransferQueue -> IO ()
-transferScannerThread st scanremotes transferqueue = do
+transferScannerThread :: ThreadState -> DaemonStatusHandle -> ScanRemoteMap -> TransferQueue -> IO ()
+transferScannerThread st dstatus scanremotes transferqueue = do
 	runEvery (Seconds 2) $ do
 		r <- getScanRemote scanremotes
 		liftIO $ debug thisThread ["starting scan of", show r]
-		scan st transferqueue r
+		scan st dstatus transferqueue r
 		liftIO $ debug thisThread ["finished scan of", show r]
 	where
 
 {- This is a naive scan through the git work tree.
  - 
  - The scan is blocked when the transfer queue gets too large. -}
-scan :: ThreadState -> TransferQueue -> Remote -> IO ()
-scan st transferqueue r = do
+scan :: ThreadState -> DaemonStatusHandle -> TransferQueue -> Remote -> IO ()
+scan st dstatus transferqueue r = do
 	g <- runThreadState st $ fromRepo id
 	files <- LsFiles.inRepo [] g
 	go files
@@ -63,7 +64,7 @@ scan st transferqueue r = do
 					| otherwise = return Nothing
 				
 		u = Remote.uuid r
-		enqueue f t = queueTransferAt smallsize Later transferqueue (Just f) t r
+		enqueue f t = queueTransferAt smallsize Later transferqueue dstatus (Just f) t r
 		smallsize = 10
 
 		{- Look directly in remote for the key when it's cheap;

Assistant/Threads/Transferrer.hs

@@ -34,12 +34,18 @@ transfererThread :: ThreadState -> DaemonStatusHandle -> TransferQueue -> Transf
 transfererThread st dstatus transferqueue slots = go
 	where
 		go = do
-			(t, info) <- getNextTransfer transferqueue
+			(t, info) <- getNextTransfer transferqueue dstatus
 			ifM (runThreadState st $ shouldTransfer dstatus t info)
 				( do
 					debug thisThread [ "Transferring:" , show t ]
+					notifyDaemonStatusChange dstatus
 					transferThread st dstatus slots t info
-				, debug thisThread [ "Skipping unnecessary transfer:" , show t ]
+				, do
+					debug thisThread [ "Skipping unnecessary transfer:" , show t ]
+					-- getNextTransfer added t to the
+					-- daemonstatus's transfer map.
+					void $ removeTransfer dstatus t
+					notifyDaemonStatusChange dstatus
 				)
 			go
 

Assistant/TransferQueue.hs

@@ -23,6 +23,7 @@ import Types.Remote
 import qualified Remote
 
 import Control.Concurrent.STM
+import qualified Data.Map as M
 
 {- The transfer queue consists of a channel listing the transfers to make;
  - the size of the queue is also tracked, and a list is maintained
@@ -58,8 +59,8 @@ stubInfo f r = TransferInfo
 
 {- Adds transfers to queue for some of the known remotes. -}
 queueTransfers :: Schedule -> TransferQueue -> DaemonStatusHandle -> Key -> AssociatedFile -> Direction -> Annex ()
-queueTransfers schedule q daemonstatus k f direction = do
-	rs <- knownRemotes <$> liftIO (getDaemonStatus daemonstatus)
+queueTransfers schedule q dstatus k f direction = do
+	rs <- knownRemotes <$> liftIO (getDaemonStatus dstatus)
 	mapM_ go =<< sufficientremotes rs
 	where
 		sufficientremotes rs
@@ -80,37 +81,48 @@ queueTransfers schedule q daemonstatus k f direction = do
 			, transferKey = k
 			, transferUUID = Remote.uuid r
 			}
-		go r = liftIO $ atomically $
-			enqueue schedule q (gentransfer r) (stubInfo f r)
+		go r = liftIO $
+			enqueue schedule q dstatus (gentransfer r) (stubInfo f r)
 
-enqueue :: Schedule -> TransferQueue -> Transfer -> TransferInfo -> STM ()
-enqueue schedule q t info
+enqueue :: Schedule -> TransferQueue -> DaemonStatusHandle -> Transfer -> TransferInfo -> IO ()
+enqueue schedule q dstatus t info
 	| schedule == Next = go unGetTChan (new:)
 	| otherwise = go writeTChan (\l -> l++[new])
 	where
 		new = (t, info)
 		go modqueue modlist = do
-			void $ modqueue (queue q) new
-			void $ modifyTVar' (queuesize q) succ
-			void $ modifyTVar' (queuelist q) modlist
+			atomically $ do
+				void $ modqueue (queue q) new
+				void $ modifyTVar' (queuesize q) succ
+				void $ modifyTVar' (queuelist q) modlist
+			void $ notifyDaemonStatusChange dstatus
 
 {- Adds a transfer to the queue. -}
-queueTransfer :: Schedule -> TransferQueue -> AssociatedFile -> Transfer -> Remote -> IO ()
-queueTransfer schedule q f t remote = atomically $
-	enqueue schedule q t (stubInfo f remote)
+queueTransfer :: Schedule -> TransferQueue -> DaemonStatusHandle -> AssociatedFile -> Transfer -> Remote -> IO ()
+queueTransfer schedule q dstatus f t remote =
+	enqueue schedule q dstatus t (stubInfo f remote)
 
 {- Blocks until the queue is no larger than a given size, and then adds a
  - transfer to the queue. -}
-queueTransferAt :: Integer -> Schedule -> TransferQueue -> AssociatedFile -> Transfer -> Remote -> IO ()
-queueTransferAt wantsz schedule q f t remote = atomically $ do
-	sz <- readTVar (queuesize q)
-	if sz <= wantsz
-		then enqueue schedule q t (stubInfo f remote)
-		else retry -- blocks until queuesize changes
+queueTransferAt :: Integer -> Schedule -> TransferQueue -> DaemonStatusHandle -> AssociatedFile -> Transfer -> Remote -> IO ()
+queueTransferAt wantsz schedule q dstatus f t remote = do
+	atomically $ do
+		sz <- readTVar (queuesize q)
+		if sz <= wantsz
+			then return ()
+			else retry -- blocks until queuesize changes
+	enqueue schedule q dstatus t (stubInfo f remote)
 
-{- Blocks until a pending transfer is available from the queue. -}
-getNextTransfer :: TransferQueue -> IO (Transfer, TransferInfo)
-getNextTransfer q = atomically $ do
+{- Blocks until a pending transfer is available from the queue.
+ - The transfer is removed from the transfer queue, and added to
+ - the daemon status currentTransfers map. This is done in a single STM
+ - transaction, so there is no window where an observer sees an
+ - inconsistent status. -}
+getNextTransfer :: TransferQueue -> DaemonStatusHandle -> IO (Transfer, TransferInfo)
+getNextTransfer q dstatus = atomically $ do
 	void $ modifyTVar' (queuesize q) pred
 	void $ modifyTVar' (queuelist q) (drop 1)
-	readTChan (queue q)
+	r@(t, info) <- readTChan (queue q)
+	adjustTransfersSTM dstatus $
+		M.insertWith' const t info
+	return r