tree 91e2313caf8a34f2edfa8fd8a6826dadaa3c4b66
parent 6f23210781666506bde36b48cf00ffc9506348b0
author Dave Borowitz <dborowitz@google.com> 1501253305 -0400
committer Dave Borowitz <dborowitz@google.com> 1501254212 -0400

RefDirectory: Add in-process fair lock for atomic updates

In a server scenario such as Gerrit Code Review, there may be many
atomic BatchRefUpdates contending for locks on both the packed-refs file
and some subset of loose refs. We already retry lock acquisition to
improve this situation slightly, but we can do better by using an
in-process lock. This way, instead of retrying and potentially exceeding
their timeout, different threads sharing the same Repository instance
can wait on a fair lock without having to touch the disk lock. Since a
server is probably already using RepositoryCache anyway, there is a high
likelihood of reusing the Repository instance.

Change-Id: If5dd1dc58f0ce62f26131fd5965a0e21a80e8bd3