b4cf22a388
I tend to prefer moving toward explicit exception handling, not away from it, but in this case, I think there are good reasons to let checkPresent throw exceptions: 1. They can all be caught in one place (Remote.hasKey), and we know every possible exception is caught there now, which we didn't before. 2. It simplified the code of the Remotes. I think it makes sense for Remotes to be able to be implemented without needing to worry about catching exceptions inside them. (Mostly.) 3. Types.StoreRetrieve.Preparer can only work on things that return a Bool, which all the other relevant remote methods already did. I do not see a good way to generalize that type; my previous attempts failed miserably.
102 lines
3 KiB
Haskell
102 lines
3 KiB
Haskell
{- Adds hooks to remotes.
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-
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- Copyright 2012 Joey Hess <joey@kitenet.net>
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-
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- Licensed under the GNU GPL version 3 or higher.
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-}
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{-# LANGUAGE CPP #-}
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module Remote.Helper.Hooks (addHooks) where
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import qualified Data.Map as M
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import Common.Annex
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import Types.Remote
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import Types.CleanupActions
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import qualified Annex
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import Annex.LockFile
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#ifndef mingw32_HOST_OS
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import Annex.Perms
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#else
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import Utility.WinLock
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#endif
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{- Modifies a remote's access functions to first run the
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- annex-start-command hook, and trigger annex-stop-command on shutdown.
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- This way, the hooks are only run when a remote is actively being used.
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-}
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addHooks :: Remote -> Remote
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addHooks r = addHooks' r
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(remoteAnnexStartCommand $ gitconfig r)
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(remoteAnnexStopCommand $ gitconfig r)
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addHooks' :: Remote -> Maybe String -> Maybe String -> Remote
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addHooks' r Nothing Nothing = r
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addHooks' r starthook stophook = r'
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where
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r' = r
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{ storeKey = \k f p -> wrapper $ storeKey r k f p
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, retrieveKeyFile = \k f d p -> wrapper $ retrieveKeyFile r k f d p
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, retrieveKeyFileCheap = \k f -> wrapper $ retrieveKeyFileCheap r k f
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, removeKey = wrapper . removeKey r
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, checkPresent = wrapper . checkPresent r
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}
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where
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wrapper = runHooks r' starthook stophook
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runHooks :: Remote -> Maybe String -> Maybe String -> Annex a -> Annex a
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runHooks r starthook stophook a = do
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dir <- fromRepo gitAnnexRemotesDir
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let lck = dir </> remoteid ++ ".lck"
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whenM (notElem lck . M.keys <$> getLockPool) $ do
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liftIO $ createDirectoryIfMissing True dir
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firstrun lck
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a
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where
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remoteid = show (uuid r)
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run Nothing = noop
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run (Just command) = void $ liftIO $
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boolSystem "sh" [Param "-c", Param command]
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firstrun lck = do
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-- Take a shared lock; This indicates that git-annex
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-- is using the remote, and prevents other instances
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-- of it from running the stophook. If another
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-- instance is shutting down right now, this
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-- will block waiting for its exclusive lock to clear.
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lockFileShared lck
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-- The starthook is run even if some other git-annex
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-- is already running, and ran it before.
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-- It would be difficult to use locking to ensure
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-- it's only run once, and it's also possible for
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-- git-annex to be interrupted before it can run the
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-- stophook, in which case the starthook
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-- would be run again by the next git-annex.
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-- So, requiring idempotency is the right approach.
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run starthook
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Annex.addCleanup (StopHook $ uuid r) $ runstop lck
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runstop lck = do
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-- Drop any shared lock we have, and take an
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-- exclusive lock, without blocking. If the lock
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-- succeeds, we're the only process using this remote,
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-- so can stop it.
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unlockFile lck
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#ifndef mingw32_HOST_OS
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mode <- annexFileMode
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fd <- liftIO $ noUmask mode $
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openFd lck ReadWrite (Just mode) defaultFileFlags
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v <- liftIO $ tryIO $
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setLock fd (WriteLock, AbsoluteSeek, 0, 0)
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case v of
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Left _ -> noop
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Right _ -> run stophook
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liftIO $ closeFd fd
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#else
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v <- liftIO $ lockExclusive lck
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case v of
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Nothing -> noop
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Just lockhandle -> do
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run stophook
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liftIO $ dropLock lockhandle
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#endif
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