transfer canceling

Should work (untested) for transfers being run by other processes.

Not yet by transfers being run by the assistant. killThread does not
kill processes forked off by a thread. To fix this, will probably
need to make `git annex getkey` and `git annex sendkey` commands that
operate on keys, and write their own transfer info. Then the assistant
can run them, and kill them, as needed.

Assistant/TransferQueue.hs

@@ -13,7 +13,8 @@ module Assistant.TransferQueue (
 	queueTransfers,
 	queueTransfer,
 	queueTransferAt,
-	getNextTransfer
+	getNextTransfer,
+	dequeueTransfer,
 ) where
 
 import Common.Annex
@@ -30,7 +31,7 @@ import qualified Data.Map as M
  - in parallel to allow for reading. -}
 data TransferQueue = TransferQueue
 	{ queue :: TChan (Transfer, TransferInfo)
-	, queuesize :: TVar Integer
+	, queuesize :: TVar Int
 	, queuelist :: TVar [(Transfer, TransferInfo)]
 	}
 
@@ -104,7 +105,7 @@ queueTransfer schedule q dstatus f t remote =
 
 {- Blocks until the queue is no larger than a given size, and then adds a
  - transfer to the queue. -}
-queueTransferAt :: Integer -> Schedule -> TransferQueue -> DaemonStatusHandle -> AssociatedFile -> Transfer -> Remote -> IO ()
+queueTransferAt :: Int -> Schedule -> TransferQueue -> DaemonStatusHandle -> AssociatedFile -> Transfer -> Remote -> IO ()
 queueTransferAt wantsz schedule q dstatus f t remote = do
 	atomically $ do
 		sz <- readTVar (queuesize q)
@@ -132,3 +133,12 @@ getNextTransfer q dstatus acceptable = atomically $ do
 				M.insertWith' const t info
 			return $ Just r
 		else return Nothing
+
+{- Removes a transfer from the queue, if present, and returns True if it
+ - was present. -}
+dequeueTransfer :: TransferQueue -> Transfer -> IO Bool
+dequeueTransfer q t = atomically $ do
+	(l, removed) <- partition (\i -> fst i /= t) <$> readTVar (queuelist q)
+	void $ writeTVar (queuesize q) (length l)
+	void $ writeTVar (queuelist q) l
+	return $ not $ null removed

Assistant/TransferSlots.hs

@@ -27,7 +27,8 @@ newTransferSlots :: IO TransferSlots
 newTransferSlots = newQSemN numSlots
 
 {- Waits until a transfer slot becomes available, and runs a transfer
- - action in the slot, in its own thread. -}
+ - action in the slot, in its own thread. Note that this thread is
+ - subject to being killed when the transfer is canceled. -}
 inTransferSlot :: TransferSlots -> ThreadState -> Annex a -> IO ThreadId
 inTransferSlot s st a = do
 	waitQSemN s 1

Assistant/WebApp/DashBoard.hs

@@ -29,6 +29,7 @@ import Yesod
 import Text.Hamlet
 import qualified Data.Map as M
 import Control.Concurrent
+import System.Posix.Signals (signalProcess, sigTERM, sigKILL)
 
 {- A display of currently running and queued transfers.
  -
@@ -161,4 +162,21 @@ startTransfer :: Transfer -> Handler ()
 startTransfer t = liftIO $ putStrLn "start"
 
 cancelTransfer :: Transfer -> Handler ()
-cancelTransfer t = liftIO $ putStrLn "cancel"
+cancelTransfer t = do
+	webapp <- getYesod
+	{- Remove if queued. -}
+	void $ liftIO $ dequeueTransfer (transferQueue webapp) t
+	{- When the transfer is running, don't directly remove it from the
+	 - map, instead signal to end the transfer, and rely on the 
+	 - TransferWatcher to notice it's done and update the map. -}
+	mi <- liftIO $ M.lookup t . currentTransfers
+		<$> getDaemonStatus (daemonStatus webapp)
+	case mi of
+		Just (TransferInfo { transferTid = Just tid } ) -> do
+			-- TODO
+			error "TODO"
+		Just (TransferInfo { transferPid = Just pid } ) -> liftIO $ do
+			signalProcess sigTERM pid
+			threadDelay 500000 -- half a second grace period
+			signalProcess sigKILL pid
+		_ -> noop