git-annex/Assistant/Threads/DaemonStatus.hs
Joey Hess 1d0b692198 webapp: Fix a race that sometimes caused alerts or other notifications to be missed if they occurred while a page was loading.
When a page is loaded, the javascript requests an notification url, and
does long polling on the url to be informed of changes. But if a change
occured before the notification url was requested, it would not be notified
of that change, and so the page display would not update.

I fixed this by *always* updating the page display after it gets
the notification url. This is extra work, but the overhead is not noticable
in the other overhead of loading a page.

(A nicer way would be to somehow record the version of a page initially
loaded, and then compare it with the current version when getting the
notification url, and only force an update if it's changed. But getting
the "version" of the different parts of the page that use long polling
is difficult.)
2013-03-27 14:56:20 -04:00

29 lines
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Haskell

{- git-annex assistant daemon status thread
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Assistant.Threads.DaemonStatus where
import Assistant.Common
import Assistant.DaemonStatus
import Utility.ThreadScheduler
import Utility.NotificationBroadcaster
{- This writes the daemon status to disk, when it changes, but no more
- frequently than once every ten minutes.
-}
daemonStatusThread :: NamedThread
daemonStatusThread = namedThread "DaemonStatus" $ do
notifier <- liftIO . newNotificationHandle False
=<< changeNotifier <$> getDaemonStatus
checkpoint
runEvery (Seconds tenMinutes) <~> do
liftIO $ waitNotification notifier
checkpoint
where
checkpoint = do
file <- liftAnnex $ fromRepo gitAnnexDaemonStatusFile
liftIO . writeDaemonStatusFile file =<< getDaemonStatus