Re: Get rid of WALBufMappingLock

26.02.2025 11:52, Andrey Borodin wrote:
>> On 25 Feb 2025, at 20:19, Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
>>
>>
>
>
> Hi!
>
> One little piece of code looks suspicious to me. But I was not raising concern because I see similar code everywhere in the codebase. But know Kirill asked to me explain what is going on and I cannot.
>
> This seems to be relevant… so.
>
> + while (upto >= pg_atomic_read_u64(&XLogCtl->InitializedUpTo))
> // Assume ConditionVariableBroadcast() happened here, but before next line
> + ConditionVariableSleep(&XLogCtl->InitializedUpToCondVar, WAIT_EVENT_WAL_BUFFER_INIT);
> + ConditionVariableCancelSleep();
>
> Won’t this sleep wait forever?

Because ConditionVariableSleep doesn't sleep for the first time.
It just performs ConditionVariablePrepareToSleep and immediately returns.
So actual condition of `while` loop is checked at least twice before going
to sleep.

>
> I see about 20 other occurrences of similar code, so, perhaps, everything is fine. But I would greatly appreciate a little pointers on why it works.

-------
regards
Yura Sokolov aka funny-falcon