I'd like to write a script that examines the incoming changesets on a push to a mercurial server and rejects the push if the changesets do not conform to a particular standard. It seems like my options are the prechangegroup, pre-changegroup, and pretxnchangegroup hooks. Unfortunately, the prechangegroup and pre-changegroup hooks do not appear to have access to the incoming changesets, so I would need pretxnchangegroup. But according to the documentation at http://hgbook.red-bean.com/read/handling-repository-events-with-hooks.html#sec:hook:pretxnchangegroup, this can lead to inconsistent state for people using the repository while the hook is executing:
"While this hook is running, if other Mercurial processes access this repository, they will be able to see the almost-added changesets as if they are permanent. This may lead to race conditions if you do not take steps to avoid them."
I'm really not crazy about random weirdness happening if someone does a pull while my script is in the process of rejecting a changeset. Is there another hook that I can use? If not, what are the "steps to avoid them" that I need to take? Is there a way I can lock the repository during my hook?
If you expand the comments for the quoted paragraph, Meister Geisler confirmed some users' observation that the issue was resolved since hg 1.2, such that the not-yet-permanent incoming changesets are not visible, thus will not be pulled.