public inbox for [email protected]  

help / color / mirror / Atom feed

From: Joel Jacobson <[email protected]>
To: Chao Li <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Rishu Bagga <[email protected]>
Subject: Re: Optimize LISTEN/NOTIFY
Date: Fri, 26 Sep 2025 11:32:29 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<CAK80=jhmE40KVqQ3ho37MArS7cAED1p9m7uikDxcnDmqdW7t8A@mail.gmail.com>
	<[email protected]>
	<[email protected]>
	<CA+hUKGLrMGkWDB0cwTa0RqD+AF7O-Ywgck8aVYKwOQnZgYRRug@mail.gmail.com>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

On Fri, Sep 26, 2025, at 04:26, Chao Li wrote:

> I think what you explained is partially correct.
>
> Based on my understanding, any backend process may call 
> SignalBackends(), which means that it’s possible that multiple backend 
> processes may call SignalBackends() concurrently.
>
> Looking at your code, between checking 
> QUEUE_BACKEND_WAKEUP_PENDING_FLAG(i) and set the flag to true, there is 
> a block of code (the “if-else”) to run, so that it’s possible that 
> multiple backend processes have passed the 
> QUEUE_BACKEND_WAKEUP_PENDING_FLAG(i) check, then multiple signals will 
> be sent to a process, which will lead to duplicate timeout enabled in 
> the receiver process.

I don't see how that can happen; we're checking wakeup_pending_flag
while holding an exclusive lock, so I don't see how multiple backend
processes could be within the region where we check/set
wakeup_pending_flag, at the same time?

/Joel

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected]
  Subject: Re: Optimize LISTEN/NOTIFY
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox