Re: Optimize LISTEN/NOTIFY

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