git-annex/Logs/Presence.hs
Joey Hess f9adb905fc
Avoid unncessary write to the location log when a file is unlocked and then added back with unchanged content.
Implemented with no additional overhead of compares etc.

This is safe to do for presence logs because of their locality of change;
a given repo's presence logs are only ever changed in that repo, or in a
repo that has just been actively changing the content of that repo.

So, we don't need to worry about a split-brain situation where there'd
be disagreement about the location of a key in a repo. And so, it's ok to
not update the timestamp when that's the only change that would be made
due to logging presence info.
2015-10-12 14:46:47 -04:00

72 lines
2.1 KiB
Haskell

{- git-annex presence log
-
- This is used to store presence information in the git-annex branch in
- a way that can be union merged.
-
- A line of the log will look like: "date N INFO"
- Where N=1 when the INFO is present, 0 otherwise.
-
- Copyright 2010-2014 Joey Hess <id@joeyh.name>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Logs.Presence (
module X,
addLog,
maybeAddLog,
readLog,
logNow,
currentLog,
currentLogInfo,
historicalLogInfo,
) where
import Data.Time.Clock.POSIX
import Logs.Presence.Pure as X
import Common.Annex
import qualified Annex.Branch
import Git.Types (RefDate)
{- Adds a LogLine to the log, removing any LogLines that are obsoleted by
- adding it. -}
addLog :: FilePath -> LogLine -> Annex ()
addLog file line = Annex.Branch.change file $ \s ->
showLog $ compactLog (line : parseLog s)
{- When a LogLine already exists with the same status and info, but an
- older timestamp, that LogLine is preserved, rather than updating the log
- with a newer timestamp.
-}
maybeAddLog :: FilePath -> LogLine -> Annex ()
maybeAddLog file line = Annex.Branch.maybeChange file $ \s -> do
m <- insertNewStatus line $ logMap $ parseLog s
return $ showLog $ mapLog m
{- Reads a log file.
- Note that the LogLines returned may be in any order. -}
readLog :: FilePath -> Annex [LogLine]
readLog = parseLog <$$> Annex.Branch.get
{- Generates a new LogLine with the current date. -}
logNow :: LogStatus -> String -> Annex LogLine
logNow s i = do
now <- liftIO getPOSIXTime
return $ LogLine now s i
{- Reads a log and returns only the info that is still in effect. -}
currentLogInfo :: FilePath -> Annex [String]
currentLogInfo file = map info <$> currentLog file
currentLog :: FilePath -> Annex [LogLine]
currentLog file = filterPresent <$> readLog file
{- Reads a historical version of a log and returns the info that was in
- effect at that time.
-
- The date is formatted as shown in gitrevisions man page.
-}
historicalLogInfo :: RefDate -> FilePath -> Annex [String]
historicalLogInfo refdate file = map info . filterPresent . parseLog
<$> Annex.Branch.getHistorical refdate file