RE: [Proposal] Add foreign-server health checks infrastructure

Dear Horiguchi-san,

Thank you for checking! The patch will be attached to another mail.

> At Fri, 27 Jan 2023 06:57:01 +0000, "Hayato Kuroda (Fujitsu)"
> <kuroda(dot)hayato(at)fujitsu(dot)com> wrote in
> > I found cfbot failure, PSA fixed version.
>
> + Unlike <xref linkend="libpq-PQstatus"/>, this function checks socket
> + health. This check is performed by polling the socket. This function is
> + currently available only on systems that support the non-standard
> + <symbol>POLLRDHUP</symbol> extension to the
> <symbol>poll</symbol> system
>
> I find it quite confusing that we have pqSocketCheck and PQconnCheck,
> that does almost the same thing.. Since pqSocketCheck is a static
> function, we can modify the function as we like.

Renamed to pqSocketIsReadableOrWritableOrValid(), but seemed very bad...

> I still don't understand why we need pqconnCheck_internal separate
> from pqSocketPoll(), and PQconnCheck from pqSocketCheck.

pqconnCheck_internal() was combined into pqSocketPoll(), but PQconnCheck() still
exists. libpq-fe.h, did not include standard header files except stdio.h. I'm not
sure whether we can add an inclusion of time.h, because it may break the compatibility
that some platform may not have the header. If there are not such a system, we may
able to export pqSocketCheck() and remove PQconnCheck().

The side effect of this changes is that codes become dirty when we add kqueue() support...

> https://www.postgresql.org/message-id/flat/TYAPR01MB58665BF23D38EDF1
> 0028DE2AF5299%40TYAPR01MB5866.jpnprd01.prod.outlook.com#47d21431bf9
> fa94f763c824f6e81fa54
> > IIUC, pqSocketCheck () calls pqSocketPoll(),
> > and in the pqSocketPoll() we poll()'d the POLLIN or POLLOUT event.
> > But according to [1], we must wait POLLRDHUP event,
> > so we cannot reuse it straightforward.
>
> Yeah, I didn't suggest to use the function as-is. Couldn't we extend
> the fucntion by letting it accept end_time = 0 && !forRead &&
> !forWrite, not causing side effects?

Modified accordingly. Is it what you expected?

Best Regards,
Hayato Kuroda
FUJITSU LIMITED