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bug#21383: Static revisions in vc-working-revision


From: Jonathan H
Subject: bug#21383: Static revisions in vc-working-revision
Date: Thu, 3 Sep 2015 10:34:08 -0700

> Indeed, mode-line updates are *very* frequent (more than once per
> command), so we really want to avoid running processes at that point.

I though the new implementation of the vc-git mode line doesn't use vc-working-revision, so in this specific case, making vc-working-revision slower won't hurt us there.

> I wonder if that's true. Caching in a property is obviously fast, and process calls are
necessarily an order of magnitude slower (and slower still on certain platforms).

True, but you have to check that the cache is invalid somehow. If you want to be super correct, a rev-parse is probably the fastest way. I suppose it would be pretty fast to check the mtime of the .git directory inside emacs and invalidate that when it changes. Although filesystem timestamps usually make me nervous, it's probably okay in this instance?



On Thu, Sep 3, 2015 at 9:17 AM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> Maybe you should write a patch and test it on Windows (or have someone else
> do it), and see whether the mode-line updates don't become
> perceptibly slower.

Indeed, mode-line updates are *very* frequent (more than once per
command), so we really want to avoid running processes at that point.


        Stefan


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