Re: Unportable implementation of background worker start

On 2017-04-21 23:50:41 -0400, Tom Lane wrote:
> Attached are a couple of patches that represent a plausible Plan B.
> The first one changes the postmaster to run its signal handlers without
> specifying SA_RESTART. I've confirmed that that seems to fix the
> select_parallel-test-takes-a-long-time problem on gaur/pademelon.

> The second one uses pselect, if available, to replace the unblock-signals/
> select()/block-signals dance in ServerLoop. On platforms where pselect
> exists and works properly, that should fix the race condition I described
> previously. On platforms where it doesn't, we're no worse off than
> before.

We probably should note somewhere prominently that pselect isn't
actually race-free on a number of platforms.

> I think that these patches represent something we could back-patch
> without a lot of trepidation, unlike the WaitEventSet-based approach.
> Therefore, my proposal is to apply and backpatch these changes, and
> call it good for v10. For v11, we could work on changing the postmaster
> to not do work in signal handlers, as discussed upthread. That would
> supersede these two patches completely, though I'd still advocate for
> keeping the change in maybe_start_bgworker.

Not yet having looked at your patches, that sounds like a reasonable
plan. I'd still like to get something like your CLOEXEC patch applied
independently however.

< patches >

Looks reasonable on a quick skim.

Greetings,

Andres Freund