add a comment about checkSaneLock

See commit 8c2dd7d8ee814614bf3c871903b5d4d2aba193f4 for original
introduction of it, but needing to spelunk that far back to understand
the code is not good.

diff --git a/Annex/Transfer.hs b/Annex/Transfer.hs
index 119c91b1af1de223abcfaca1a968cda0004a115b..315033d21908e39f7afc970f42378a004c705bf7 100644 (file)
--- a/Annex/Transfer.hs
+++ b/Annex/Transfer.hs
@@ -151,6 +151,11 @@ runTransfer' ignorelock t afile stalldetection retrydecider transferaction =
                createAnnexDirectory $ P.takeDirectory lck
                tryLockExclusive (Just mode) lck >>= \case
                        Nothing -> return (Nothing, True)
+                       -- Since the lock file is removed in cleanup,
+                       -- there's a race where different processes
+                       -- may have a deleted and a new version of the same
+                       -- lock file open. checkSaneLock guards against
+                       -- that.
                        Just lockhandle -> ifM (checkSaneLock lck lockhandle)
                                ( do
                                        createtfile