Function ExecAppendAsyncEventWait

src/backend/executor/nodeAppend.c:1059–1138

---------------------------------------------------------------- * ExecAppendAsyncEventWait * * Wait or poll for file descriptor events and fire callbacks. * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static void
ExecAppendAsyncEventWait(AppendState *node)
{
	int			nevents = node->as_nasyncplans + 1;
	long		timeout = node->as_syncdone ? -1 : 0;
	WaitEvent	occurred_event[EVENT_BUFFER_SIZE];
	int			noccurred;
	int			i;

	/* We should never be called when there are no valid async subplans. */
	Assert(node->as_nasyncremain > 0);

	node->as_eventset = CreateWaitEventSet(CurrentMemoryContext, nevents);
	AddWaitEventToSet(node->as_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
					  NULL, NULL);

	/* Give each waiting subplan a chance to add an event. */
	i = -1;
	while ((i = bms_next_member(node->as_asyncplans, i)) >= 0)
	{
		AsyncRequest *areq = node->as_asyncrequests[i];

		if (areq->callback_pending)
			ExecAsyncConfigureWait(areq);
	}

	/*
	 * No need for further processing if there are no configured events other
	 * than the postmaster death event.
	 */
	if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
	{
		FreeWaitEventSet(node->as_eventset);
		node->as_eventset = NULL;
		return;
	}

	/* We wait on at most EVENT_BUFFER_SIZE events. */
	if (nevents > EVENT_BUFFER_SIZE)
		nevents = EVENT_BUFFER_SIZE;

	/*
	 * If the timeout is -1, wait until at least one event occurs.  If the
	 * timeout is 0, poll for events, but do not wait at all.
	 */
	noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
								 nevents, WAIT_EVENT_APPEND_READY);
	FreeWaitEventSet(node->as_eventset);
	node->as_eventset = NULL;
	if (noccurred == 0)
		return;

	/* Deliver notifications. */
	for (i = 0; i < noccurred; i++)
	{
		WaitEvent  *w = &occurred_event[i];

		/*