use separate lock from content file in v9

Windows has always used a separate lock file, but on unix, the content
file itself was locked, and in v9 that changes to also use a separate
lock file.

This needs to be tested more. Eg, what happens after dropping a file;
does the the content lock file get deleted too, or linger around?

Sponsored-by: Dartmouth College's Datalad project

diff --git a/Annex/Content.hs b/Annex/Content.hs
index 68d21506f12da7d745e4288f100ee3ef6bf2ee64..d56d2f88241a08c2a961edb54dbd13ac66c2c5cb 100644 (file)
--- a/Annex/Content.hs
+++ b/Annex/Content.hs
@@ -115,8 +115,8 @@ lockContentShared key a = lockContentUsing lock key notpresent $
   where
        notpresent = giveup $ "failed to lock content: not present"
 #ifndef mingw32_HOST_OS
-       lock contentfile Nothing = tryLockShared Nothing contentfile
        lock _ (Just lockfile) = posixLocker tryLockShared lockfile
+       lock contentfile Nothing = tryLockShared Nothing contentfile
 #else
        lock = winLocker lockShared
 #endif
@@ -126,21 +126,25 @@ lockContentShared key a = lockContentUsing lock key notpresent $
  -
  - If locking fails, throws an exception rather than running the action.
  -
- - But, if locking fails because the the content is not present, runs the
- - fallback action instead.
+ - If locking fails because the the content is not present, runs the
+ - fallback action instead. However, the content is not guaranteed to be
+ - present when this succeeds.
  -}
 lockContentForRemoval :: Key -> Annex a -> (ContentRemovalLock -> Annex a) -> Annex a
 lockContentForRemoval key fallback a = lockContentUsing lock key fallback $ 
        a (ContentRemovalLock key)
   where
 #ifndef mingw32_HOST_OS
-       {- Since content files are stored with the write bit disabled, have
-        - to fiddle with permissions to open for an exclusive lock. -}
-       lock contentfile Nothing = bracket_
-               (thawContent contentfile)
-               (freezeContent contentfile)
-               (tryLockExclusive Nothing contentfile)
        lock _ (Just lockfile) = posixLocker tryLockExclusive lockfile
+       {- No lock file, so the content file itself is locked. 
+        - Since content files are stored with the write bit
+        - disabled, have to fiddle with permissions to open
+        - for an exclusive lock. -}
+       lock contentfile Nothing = 
+               bracket_
+                       (thawContent contentfile)
+                       (freezeContent contentfile)
+                       (tryLockExclusive Nothing contentfile)
 #else
        lock = winLocker lockExclusive
 #endif
@@ -170,7 +174,7 @@ winLocker _ _ Nothing = return Nothing
 {- The fallback action is run if the ContentLocker throws an IO exception
  - and the content is not present. It's not guaranteed to always run when
  - the content is not present, because the content file is not always
- - the file that is locked eg on Windows a different file is locked. -}
+ - the file that is locked. -}
 lockContentUsing :: ContentLocker -> Key -> Annex a -> Annex a -> Annex a
 lockContentUsing locker key fallback a = do
        contentfile <- calcRepo (gitAnnexLocation key)

diff --git a/Annex/Content/Presence.hs b/Annex/Content/Presence.hs
index 07f77ec59d946ee85ca67b00ccc0a7258636bdbd..df57716220e63c30674a52f6a19b24d68d328633 100644 (file)
--- a/Annex/Content/Presence.hs
+++ b/Annex/Content/Presence.hs
@@ -24,6 +24,7 @@ import Annex.Content.Presence.LowLevel
 import Annex.Common
 import qualified Annex
 import Annex.LockPool
+import Annex.Version
 import qualified Database.Keys
 import Annex.InodeSentinal
 import Utility.InodeCache
@@ -115,13 +116,19 @@ inAnnexSafe key = inAnnex' (fromMaybe True) (Just False) go key
                        )
 #endif
 
-{- Windows has to use a separate lock file from the content, since
- - locking the actual content file would interfere with the user's
- - use of it. -}
 contentLockFile :: Key -> Annex (Maybe RawFilePath)
 #ifndef mingw32_HOST_OS
-contentLockFile _ = pure Nothing
+{- Older versions of git-annex locked content files themselves, but newer
+ - versions use a separate lock file, to better support repos shared
+ - amoung users in eg a group. -}
+contentLockFile key = ifM (versionNeedsWritableContentFiles <$> getVersion)
+       ( pure Nothing
+       , Just <$> calcRepo (gitAnnexContentLock key)
+       )
 #else
+{- Windows always has to use a separate lock file from the content, since
+ - locking the actual content file would interfere with the user's
+ - use of it. -}
 contentLockFile key = Just <$> calcRepo (gitAnnexContentLock key)
 #endif