Re: Optimize LISTEN/NOTIFY

On Sep 26, 2025, at 17:32, Joel Jacobson <joel@compiler.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