The commenter you are replying to is a former Google employee; the description of the lock service sounds like Chubby (http://research.google.com/archive/chubby

The commenter you are replying to is a former Google employee; the description of the lock service sounds like Chubby (http://research.google.com/archive/chubby.html http://research.google.com/archive/chubby.html), App Engine likely uses some sort of distributed directory service for keeping track of things like quotas.