Re: Optimize LISTEN/NOTIFY

On Wed, Jul 23, 2025 at 1:39 PM Joel Jacobson <joel(at)compiler(dot)org> wrote:
> In their patch, in asyn.c's SignalBackends(), they do
> SendInterrupt(INTERRUPT_ASYNC_NOTIFY, procno) instead of
> SendProcSignal(pid, PROCSIG_NOTIFY_INTERRUPT, procnos[i]). They don't
> seem to check if the backend is already signalled or not, but maybe
> SendInterrupt() has signal coalescing built-in so it would be a noop
> with almost no cost?

Yeah:

+ old_pending = pg_atomic_fetch_or_u32(&proc->pendingInterrupts, interruptMask);
+
+ /*
+ * If the process is currently blocked waiting for an interrupt to arrive,
+ * and the interrupt wasn't already pending, wake it up.
+ */
+ if ((old_pending & (interruptMask | SLEEPING_ON_INTERRUPTS)) ==
SLEEPING_ON_INTERRUPTS)
+ WakeupOtherProc(proc);