git-annex/Assistant/Threads/TransferPoller.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

56 lines
1.8 KiB
Haskell

{- git-annex assistant transfer polling thread
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Assistant.Threads.TransferPoller where
import Assistant.Common
import Assistant.DaemonStatus
import Logs.Transfer
import Utility.NotificationBroadcaster
import qualified Assistant.Threads.TransferWatcher as TransferWatcher
import Control.Concurrent
import qualified Data.Map as M
{- This thread polls the status of ongoing transfers, determining how much
- of each transfer is complete. -}
transferPollerThread :: NamedThread
transferPollerThread = namedThread "TransferPoller" $ do
g <- liftAnnex gitRepo
tn <- liftIO . newNotificationHandle True =<<
transferNotifier <$> getDaemonStatus
forever $ do
liftIO $ threadDelay 500000 -- 0.5 seconds
ts <- currentTransfers <$> getDaemonStatus
if M.null ts
-- block until transfers running
then liftIO $ waitNotification tn
else mapM_ (poll g) $ M.toList ts
where
poll g (t, info)
{- Downloads are polled by checking the size of the
- temp file being used for the transfer. -}
| transferDirection t == Download = do
let f = gitAnnexTmpLocation (transferKey t) g
sz <- liftIO $ catchMaybeIO $
fromIntegral . fileSize <$> getFileStatus f
newsize t info sz
{- Uploads don't need to be polled for when the TransferWatcher
- thread can track file modifications. -}
| TransferWatcher.watchesTransferSize = noop
{- Otherwise, this code polls the upload progress
- by reading the transfer info file. -}
| otherwise = do
let f = transferFile t g
mi <- liftIO $ catchDefaultIO Nothing $
readTransferInfoFile Nothing f
maybe noop (newsize t info . bytesComplete) mi
newsize t info sz
| bytesComplete info /= sz && isJust sz =
alterTransferInfo t $ \i -> i { bytesComplete = sz }
| otherwise = noop