[PATCH V2] revset: fix generatorset race condition

[David Soria Parra]

Durham Goode <durham at fb.com> writes:

> # HG changeset patch
> # User Durham Goode <durham at fb.com>
> # Date 1395789007 25200
> #      Tue Mar 25 16:10:07 2014 -0700
> # Node ID c28ab989810ae838379b8964dbdd53a300a53c92
> # Parent  9a09a625bc93ab69248613abcbea041b785f1a0e
> revset: fix generatorset race condition
>
> If two things were iterating over a generatorset at the same time, they could
> miss out on the things the other was generating, resulting in incomplete
> results. This fixes it by making it possible for two things to iterate at once,
> by always checking the _genlist at the beginning of each iteration.
>
> I was only able to repro it with pending changes from my other commits, but they
> aren't ready yet. So I'm unable to add a test for now.
>

this looks good to me, but I'll leave it for matt or crew to queue it.