Function ExecAppendAsyncRequest

src/backend/executor/nodeAppend.c:1005–1051

---------------------------------------------------------------- * ExecAppendAsyncRequest * * Request a tuple asynchronously. * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static bool
ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
{
	Bitmapset  *needrequest;
	int			i;

	/* Nothing to do if there are no async subplans needing a new request. */
	if (bms_is_empty(node->as_needrequest))
	{
		Assert(node->as_nasyncresults == 0);
		return false;
	}

	/*
	 * If there are any asynchronously-generated results that have not yet
	 * been returned, we have nothing to do; just return one of them.
	 */
	if (node->as_nasyncresults > 0)
	{
		--node->as_nasyncresults;
		*result = node->as_asyncresults[node->as_nasyncresults];
		return true;
	}

	/* Make a new request for each of the async subplans that need it. */
	needrequest = node->as_needrequest;
	node->as_needrequest = NULL;
	i = -1;
	while ((i = bms_next_member(needrequest, i)) >= 0)
	{
		AsyncRequest *areq = node->as_asyncrequests[i];

		/* Do the actual work. */
		ExecAsyncRequest(areq);
	}
	bms_free(needrequest);

	/* Return one of the asynchronously-generated results if any. */
	if (node->as_nasyncresults > 0)
	{
		--node->as_nasyncresults;
		*result = node->as_asyncresults[node->as_nasyncresults];
		return true;
	}

	return false;
}

/* ----------------------------------------------------------------
 *		ExecAppendAsyncEventWait