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Date: Wed, 22 Nov 2023 11:29:42 -0600
Message-Id: <CX5IOLTR8MAD.1UUDEG0X673Z4@neon.tech>
Subject: Re: psql not responding to SIGINT upon db reconnection
To: "Heikki Linnakangas" <hlinnaka@iki.fi>
From: "Tristan Partin" <tristan@neon.tech>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>, <pgsql-hackers@postgresql.org>, "Shlok
 Kyal" <shlok.kyal.oss@gmail.com>
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On Thu Nov 16, 2023 at 8:33 AM CST, Heikki Linnakangas wrote:
> On 06/11/2023 19:16, Tristan Partin wrote:
> >>> That sounds like a much better solution. Attached you will find a v4
> >>> that implements your suggestion. Please let me know if there is
> >>> something that I missed. I can confirm that the patch works.
>
> This patch is missing a select(). It will busy loop until the connection=
=20
> is established or cancelled.

If I add a wait (select, poll, etc.), then I can't control-C during the=20
blocking call, so it doesn't really solve the problem. On Linux, we have=20
signalfds which seem like the perfect solution to this problem, "wait on=20
the pq socket or SIGINT." But that doesn't translate well to other=20
operating systems :(.

> tristan957=3D> \c
> NOTICE:  Welcome to Neon!
> Authenticate by visiting:
>     https://console.neon.tech/psql_session/XXXX
>=20
>=20
> ^CTerminated

You can see here that I can't terminate the command. Where you see=20
"Terminated" is me running `kill $(pgrep psql)` in another terminal.

> Shouldn't we also clear CancelRequested after we have cancelled the=20
> attempt? Otherwise, any subsequent attempts will immediately fail too.

After switching to cancel_pressed, I don't think so. See this bit of=20
code in the psql main loop:

> /* main loop to get queries and execute them */
> while (successResult =3D=3D EXIT_SUCCESS)
> {
> 	/*
> 	 * Clean up after a previous Control-C
> 	 */
> 	if (cancel_pressed)
> 	{
> 		if (!pset.cur_cmd_interactive)
> 		{
> 			/*
> 			 * You get here if you stopped a script with Ctrl-C.
> 			 */
> 			successResult =3D EXIT_USER;
> 			break;
> 		}
>=20
> 		cancel_pressed =3D false;
> 	}

> Should we use 'cancel_pressed' here rather than CancelRequested? To be=20
> honest, I don't understand the difference, so that's a genuine question.=
=20
> There was an attempt at unifying them in the past but it was reverted in=
=20
> commit 5d43c3c54d.

The more I look at this, the more I don't understand... I need to look=20
at this harder, but wanted to get this email out. Switched to=20
cancel_pressed though. Thanks for pointing it out. Going to wait to send=20
a v2 while more discussion occurs.

--=20
Tristan Partin
Neon (https://neon.tech)