This is the article you speak of: http://githubengineering.com/git-concurrency-in-github-deskt...
The AsyncReaderWriterLock mentioned in blog does not directly show up in Google, but it appears to be based on the one in this blog post: http://blogs.msdn.com/b/pfxteam/archive/2012/02/12/building-...
I also remember some blog post going into sync/async details of git.exe vs libgit2 stuff. Will try to google it.