assistant: Detect stale git lock files at startup time, and remove them.

Extends the index.lock handling to other git lock files. I surveyed
all lock files used by git, and found more than I expected. All are
handled the same in git; it leaves them open while doing the operation,
possibly writing the new file content to the lock file, and then closes
them when done.

The gc.pid file is excluded because it won't affect the normal operation
of the assistant, and waiting for a gc to finish on startup wouldn't be
good.

All threads except the webapp thread wait on the new startup sanity checker
thread to complete, so they won't try to do things with git that fail
due to stale lock files. The webapp thread mostly avoids doing that kind of
thing itself. A few configurators might fail on lock files, but only if the
user is explicitly trying to run them. The webapp needs to start
immediately when the user has opened it, even if there are stale lock
files.

Arranging for the threads to wait on the startup sanity checker was a bit
of a bear. Have to get all the NotificationHandles set up before the
startup sanity checker runs, or they won't see its signal. Perhaps
the NotificationBroadcaster is not the best interface to have used for
this. Oh well, it works.

This commit was sponsored by Michael Jakl

Assistant/NamedThread.hs

@@ -16,6 +16,7 @@ import Assistant.Types.DaemonStatus
 import Assistant.Types.UrlRenderer
 import Assistant.DaemonStatus
 import Assistant.Monad
+import Utility.NotificationBroadcaster
 
 import Control.Concurrent
 import Control.Concurrent.Async
@@ -34,7 +35,7 @@ import qualified Data.Text as T
  - Named threads are run by a management thread, so if they crash
  - an alert is displayed, allowing the thread to be restarted. -}
 startNamedThread :: UrlRenderer -> NamedThread -> Assistant ()
-startNamedThread urlrenderer namedthread@(NamedThread name a) = do
+startNamedThread urlrenderer (NamedThread afterstartupsanitycheck name a) = do
 	m <- startedThreads <$> getDaemonStatus
 	case M.lookup name m of
 		Nothing -> start
@@ -44,14 +45,24 @@ startNamedThread urlrenderer namedthread@(NamedThread name a) = do
 				Right Nothing -> noop
 				_ -> start
   where
-	start = do
+	start
+		| afterstartupsanitycheck = do
+			status <- getDaemonStatus
+			h <- liftIO $ newNotificationHandle False $
+				startupSanityCheckNotifier status
+			startwith $ runmanaged $
+				liftIO $ waitNotification h
+		| otherwise = startwith $ runmanaged noop
+	startwith runner = do
 		d <- getAssistant id
-		aid <- liftIO $ runmanaged $ d { threadName = name }
-		restart <- asIO $ startNamedThread urlrenderer namedthread
+		aid <- liftIO $ runner $ d { threadName = name }
+		restart <- asIO $ startNamedThread urlrenderer (NamedThread False name a)
 		modifyDaemonStatus_ $ \s -> s
 			{ startedThreads = M.insertWith' const name (aid, restart) (startedThreads s) }
-	runmanaged d = do
-		aid <- async $ runAssistant d a
+	runmanaged first d = do
+		aid <- async $ runAssistant d $ do
+			void first
+			a
 		void $ forkIO $ manager d aid
 		return aid
 	manager d aid = do
@@ -75,7 +86,7 @@ startNamedThread urlrenderer namedthread@(NamedThread name a) = do
 #endif
 
 namedThreadId :: NamedThread -> Assistant (Maybe ThreadId)
-namedThreadId (NamedThread name _) = do
+namedThreadId (NamedThread _ name _) = do
 	m <- startedThreads <$> getDaemonStatus
 	return $ asyncThreadId . fst <$> M.lookup name m