Re: Fix a race condition in ConditionVariableTimedSleep()

Hi,

On Mon, May 05, 2025 at 02:15:15PM +0300, Yura Sokolov wrote:
> Interestingly, our colleague stepped into same problem recently [1] . It
> happened because he attempted to make overcomplex timeout (SIGALARM) handler.
>
> But his solution was a bit different [2].
>
> [1] https://postgr.es/m/076eb7bd-52e6-4a51-ba00-c744d027b15c@postgrespro.ru
> [2]
> https://postgr.es/m/attachment/175030/0001-CV-correctly-handle-cv_sleep_target-change.patch
>
> And I believe, his solution is more elegant. Doesn't it?

I'm not sure as it'd not maintain the initial intent to re-add to the
wait list.

> But in first step, I doubt there should be any thing that cancels condition
> variable during WaitLatch.

I'm not 100% sure.

> Most probably you did wrong thing.

I "just" added an ereport(LOG,..) that has been enough to cancel the condition
variable and trigger the failed assertion. I agree that you could still consider
this as wrong thing if you think that we should not do anything that cancels
condition variable during WaitLatch though.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com