tree 8451d55f29c57191f7c8f9ac3f3b7de1534838ab
parent cf9e3fad524f5c4a47144decd9091c84c3f07849
author Dave Borowitz <dborowitz@google.com> 1499276739 -0400
committer Dave Borowitz <dborowitz@google.com> 1501002890 -0400

Implement atomic BatchRefUpdates for RefDirectory

The existing packed-refs file provides a mechanism for implementing
atomic multi-ref updates without any changes to the on-disk format or
lockfile protocol. We just need to make sure that there are no loose
refs involved in the transaction, which we can achieve by packing the
refs while holding locks on all loose refs. Full details of the
algorithm are in the PackedBatchRefUpdate javadoc.

This change does not implement reflog support, which will come in a
later change.

Change-Id: I09829544a0d4e8dbb141d28c748c3b96ef66fee1