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Re: Reducing redundant build at Travis?

On Fri, Jul 14, 2017 at 07:54:16AM -0700, Junio C Hamano wrote:

> > The "git test" script[1] uses this strategy with git-notes as the
> > storage, and I've found it quite useful. I don't think we can rely on
> > git-notes, but I think Travis gives us some storage options. Even just a
> > best-effort cache directory would probably be sufficient (this is an
> > optimization, after all).
> We do seem to use some persistence to order prove tests already, but
> I do not think it helps the common case, where my end-of-day push
> pushes out 'maint' and 'v2.13.3' at the same time, because the push
> is made with "git push --follow-tags $there maint master next pu"
> and the new tag happens to be at 'maint'.  It would be nice if
> Travis runs were sequential, but I often observe that it creates
> jobs for these multiple branches and tags pushed at the same time,
> and start running a few of them.

Ah, right, I didn't think about how these are racing. You'd need storage
which allows some kind of atomic operation to "claim" the tree as a
work-in-progress (and anybody who loses the race to get the lock would
have to spin waiting for the winner to tell them the real status).

I don't know if Travis's cache storage is up to that challenge. We could
probably build such a lock on top of third-party storage, but things are
rapidly getting more complex.