cache: move open to thread pool

[Ka-Hing Cheung]

Unfortunately our test colo is not setup to do performance testing
(the traffic it receives varies too much). We do intend to merge this
to our production colos but there's no timeline yet.

Yuchen (CC'ed) will be the main contact from now on as today is my
last day at Cloudflare.

- Ka-Hing

On Thu, Feb 7, 2019 at 5:39 AM Maxim Konovalov <maxim at nginx.com> wrote:
>
> Great.  Thanks for the testing!
>
> Did you see any measurable perf. metrics changes comparing to your
> aio open implementation or comparing to nginx without aio open support?
>
> We are still waiting for additional input from another tester, who
> expressed interest before.
>
> Thanks,
>
> Maxim
>
> On 07/02/2019 00:19, Ka-Hing Cheung wrote:
> > This has been running in our test colo for the past week with no ill effects.
> >
> > On Wed, Jan 23, 2019 at 4:39 AM Maxim Konovalov <maxim at nginx.com> wrote:
> >>
> >> Hi Ka-Hing,
> >>
> >> Roman told me that the delta is because of your changes.
> >>
> >> Thanks for your time on that.  Waiting for your testing results.
> >>
> >> Maxim
> >>
> >> On 22/01/2019 22:34, Ka-Hing Cheung via nginx-devel wrote:
> >>> I spoke too soon, just realized our test colo is running the patches
> >>> without aio_open on. Flipping that switch now.
> >>>
> >>> Also, including the patch that we applied on top in addition to the
> >>> massaging we did to resolve conflicts. I haven't dug too deep to see
> >>> if stock nginx also requires similar changes or they are only
> >>> necessary because of our other nginx changes:
> >>>
> >> [...]
> >>
> >> --
> >> Maxim Konovalov
>
>
> --
> Maxim Konovalov