Function ProcessIncomingNotify

src/backend/commands/async.c:2252–2295

* ProcessIncomingNotify * * Scan the queue for arriving notifications and report them to the front * end. The notifications might be from other sessions, or our own; * there's no need to distinguish here. * * If "flush" is true, force any frontend messages out immediately. * * NOTE: since we are outside any transaction, we must create our own. */

 *		NOTE: since we are outside any transaction, we must create our own.
 */
static void
ProcessIncomingNotify(bool flush)
{
	bool		client_wait_timeout_enabled;

	/* We *must* reset the flag */
	notifyInterruptPending = false;

	/* Do nothing else if we aren't actively listening */
	if (listenChannels == NIL)
		return;

	client_wait_timeout_enabled = DisableClientWaitTimeoutInterrupt();

	if (Trace_notify)
		elog(DEBUG1, "ProcessIncomingNotify");

	set_ps_display("notify interrupt");

	/*
	 * We must run asyncQueueReadAllNotifications inside a transaction, else
	 * bad things happen if it gets an error.
	 */
	StartTransactionCommand();

	asyncQueueReadAllNotifications();

	CommitTransactionCommand();

	/*
	 * If this isn't an end-of-command case, we must flush the notify messages
	 * to ensure frontend gets them promptly.
	 */
	if (flush)
		pq_flush();

	set_ps_display("idle");

	if (Trace_notify)
		elog(DEBUG1, "ProcessIncomingNotify: done");

	if (client_wait_timeout_enabled)
		EnableClientWaitTimeoutInterrupt();
}

/*
 * Send NOTIFY message to my front end.