Re: [PoC] Federated Authn/z with OAUTHBEARER - Mailing list pgsql-hackers

On Sat, May 20, 2023 at 10:01 AM Jacob Champion <jchampion@timescale.com> wrote:
> - The client implementation is currently epoll-/Linux-specific. I think
> kqueue shouldn't be too much trouble for the BSDs, but it's even more
> code to maintain.

I guess you also need a fallback that uses plain old POSIX poll()?  I
see you're not just using epoll but also timerfd.  Could that be
converted to plain old timeout bookkeeping?  That should be enough to
get every other Unix and *possibly* also Windows to work with the same
code path.

> - Unless someone is aware of some amazing Winsock magic, I'm pretty sure
> the multiplexed-socket approach is dead in the water on Windows. I think
> the strategy there probably has to be a background thread plus a fake
> "self-pipe" (loopback socket) for polling... which may be controversial?

I am not a Windows user or hacker, but there are certainly several
ways to multiplex sockets.  First there is the WSAEventSelect() +
WaitForMultipleObjects() approach that latch.c uses.  It has the
advantage that it allows socket readiness to be multiplexed with
various other things that use Windows "events".  But if you don't need
that, ie you *only* need readiness-based wakeup for a bunch of sockets
and no other kinds of fd or object, you can use winsock's plain old
select() or its fairly faithful poll() clone called WSAPoll().  It
looks a bit like that'd be true here if you could kill the timerfd?

It's a shame to write modern code using select(), but you can find
lots of shouting all over the internet about WSAPoll()'s defects, most
famously the cURL guys[1] whose blog is widely cited, so people still
do it.  Possibly some good news on that front:  by my reading of the
docs, it looks like that problem was fixed in Windows 10 2004[2] which
itself is by now EOL, so all systems should have the fix?  I suspect
that means that, finally, you could probably just use the same poll()
code path for Unix (when epoll is not available) *and* Windows these
days, making porting a lot easier.  But I've never tried it, so I
don't know what other problems there might be.  Another thing people
complain about is the lack of socketpair() or similar in winsock which
means you unfortunately can't easily make anonymous
select/poll-compatible local sockets, but that doesn't seem to be
needed here.

[1] https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/
[2] https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsapoll