MIME-Version: 1.0
References: 
 <CAOYmi+nDZxJHaWj9_jRSyf8uMToCADAmOfJEggsKW-kY7aUwHA@mail.gmail.com>
 <CAOYmi+mRhhzGUvrcdickepAnsdaGbqhNcboNe4-YvgtkSzGNbQ@mail.gmail.com>
 <CA+hUKGLyS-GK_rkENaVbFVTa4VJ+reJxWtt+q4gmgNUXhptfYA@mail.gmail.com>
 <CAOYmi+k1q3feeMxfbaJA=+hx+XnOFQA0z2JU+0igA7fTUZTmoA@mail.gmail.com>
 <CA+hUKG+H1gwDh96jn5jB6Q3HyXrSC9x2y=uQJAthT8NLs6GN_Q@mail.gmail.com>
In-Reply-To: 
 <CA+hUKG+H1gwDh96jn5jB6Q3HyXrSC9x2y=uQJAthT8NLs6GN_Q@mail.gmail.com>
From: Jacob Champion <jacob.champion@enterprisedb.com>
Date: Wed, 6 Aug 2025 09:13:32 -0700
Message-ID: 
 <CAOYmi+n1xRNCDnwZzigXVk8V=+sr7ZzuGpJ0tAyozX-zQT19Gg@mail.gmail.com>
Subject: Re: [PATCH] OAuth: fix performance bug with stuck multiplexer events
To: Thomas Munro <thomas.munro@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Daniel Gustafsson <daniel@yesql.se>,
	Peter Eisentraut <peter@eisentraut.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: 
 <https://www.postgresql.org/message-id/CAOYmi%2Bn1xRNCDnwZzigXVk8V%3D%2Bsr7ZzuGpJ0tAyozX-zQT19Gg%40mail.gmail.com>
Precedence: bulk

On Wed, Aug 6, 2025 at 8:04=E2=80=AFAM Thomas Munro <thomas.munro@gmail.com=
> wrote:
>  * If it returns 1, then it stopped on the first level-triggered event
> that it rechecked and found to be still true.  Who cares if there are
> more that didn't get rechecked?  poll(fd) will report POLLIN either
> way, and that's what you want.

I think the weaker guarantee might be sufficient. I was trying to get
a stronger primitive in place so that we wouldn't have to worry about
it down the line, but it is a lot of code to pay...

One sharp edge of that strategy is caught by the new tests, which is
that if you call drain_socket_events() and then unset the timer, your
multiplexer is still readable until you call drain_socket_events() yet
again. At the moment, our code only ever calls those two in the
opposite order (due to the race condition pointed out in 0002); we'd
just have to keep that in mind. Maybe "drain" would no longer be the
verb to use there.

--Jacob