fix liveupdate locking

This fixes the build on windows.

Changed it to use lock pools, which will behave better if two threads
call getLiveRepoSizes at the same time.

Also this should make it work when annex.pidlock is set. In that case,
once the current process locks this file, or anything, any other process
will have to wait on the pid lock. So checkStaleSizeChanges will
correctly identify any other live changes in the database as stale,
since there can only be one git-annex process running.

Annex/LockFile.hs

@@ -1,6 +1,6 @@
 {- git-annex lock files.
  -
- - Copyright 2012-2020 Joey Hess <id@joeyh.name>
+ - Copyright 2012-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -16,6 +16,7 @@ module Annex.LockFile (
 	withExclusiveLock,
 	takeExclusiveLock,
 	tryExclusiveLock,
+	trySharedLock,
 ) where
 
 import Annex.Common
@@ -111,3 +112,16 @@ tryExclusiveLock lockfile a = debugLocks $ do
 	unlock = maybe noop dropLock
 	go Nothing = return Nothing
 	go (Just _) = Just <$> a
+
+{- Tries to take a shared lock, without blocking.
+ -
+ - Does not create the lock directory or lock file if it does not exist,
+ - taking an exclusive lock will create them.
+ -}
+trySharedLock :: RawFilePath -> Annex (Maybe LockHandle)
+trySharedLock lockfile = debugLocks $
+#ifndef mingw32_HOST_OS
+	tryLockShared Nothing lockfile
+#else
+	liftIO $ lockShared lockfile
+#endif

Annex/RepoSize/LiveUpdate.hs

@@ -177,7 +177,7 @@ checkStaleSizeChanges h@(RepoSizeHandle (Just _) livev) = do
 
 	checkstale livedir lockfile pid =
 		let f = livedir P.</> toRawFilePath lockfile
-		in tryLockShared Nothing f >>= \case
+		in trySharedLock f >>= \case
 			Nothing -> return Nothing
 			Just lck -> do
 				return $ Just