Commits on Dec 20, 2019

1. gvfs-helper: better support for concurrent packfile fetches …

   Teach gvfs-helper to better support the concurrent fetching of the
   same packfile by multiple instances.
   
   If 2 instances of gvfs-helper did a POST and requested the same set of
   OIDs, they might receive the exact same packfile (same checksum SHA).
   Both processes would then race to install their copy of the .pack and
   .idx files into the ODB/pack directory.
   
   This is not a problem on Unix (because of filesystem semantics).
   
   On Windows, this can cause an EBUSY/EPERM problem for the loser while
   the winner is holding a handle to the target files.  (The existing
   packfile code already handled simple the existence and/or replacement
   case.)
   
   The solution presented here is to silently let the loser claim
   victory IIF the .pack and .idx are already present in the ODB.
   (We can't check this in advance because we don't know the packfile
   SHA checksum until after we receive it and run index-pack.)
   
   We avoid using a per-packfile lockfile (or a single lockfile for
   the `vfs-` prefix) to avoid the usual issues with stale lockfiles.
   
   Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

   

   jeffhostetler committed Dec 20, 2019
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