Message-ID: <de93d338-fc4d-4184-856a-b2c19eca0499@iki.fi>
Date: Tue, 7 Jul 2026 01:12:57 +0300
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Don't use the deprecated and insecure PQcancel in our frontend
 tools anymore
To: Jelte Fennema-Nio <postgres@jeltef.nl>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Alvaro Herrera <alvherre@alvh.no-ip.org>,
 Jacob Champion <jacob.champion@enterprisedb.com>
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 <DG9TD0OX13DP.2JAB9LIS2HTLO@jeltef.nl>
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 <9d7ba3ac-d660-483e-8f68-9096a2464e90@iki.fi>
 <DH3G8Z262WNH.DMDDI1DM95OG@jeltef.nl>
 <d102a894-409b-43cd-a164-eaf416077ff4@iki.fi>
 <DH4ZKYOWSPRN.2L0Z3WDBG9FC8@jeltef.nl>
 <b0e6a640-5aed-469f-867a-cc820b046798@iki.fi>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
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On 04/07/2026 01:28, Jelte Fennema-Nio wrote:
> On Tue, 7 Apr 2026 at 02:18, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>> The cancel handling in wait_on_slots() in parallel_slot.c is surprising
>> in a different way. It already uses async libpq calls and has a select()
>> loop, but it still relies on the signal handler to do the cancellation.
>> And it arbitrarily PQcancel()s only one of the connections it waits on.
> 
> Addressed this in 0002

This relies on the signal to interrupt select(), but I'm afraid that's 
not guaranteed on all platforms. Also, there's a race condition if the 
signal arrives *just* before you call select(). That's what the 
"self-pipe hack" is for, see comments at waiteventset.c.

- Heikki