Re: Optimize LISTEN/NOTIFY

> On Sep 26, 2025, at 17:32, Joel Jacobson <joel(at)compiler(dot)org> wrote:
>
> 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

I might miss the factor of holding an exclusive lock. I will revisit that part again.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/