Function ExecMakeFunctionResultSet

src/backend/executor/execSRF.c:500–693

* ExecMakeFunctionResultSet * * Evaluate the arguments to a set-returning function and then call the * function itself. The argument expressions may not contain set-returning * functions (the planner is supposed to have separated evaluation for those). * * This should be called in a short-lived (per-tuple) context, argContext * needs to live until all rows have been returned (i.e. *isDone

 * This is used by nodeProjectSet.c.
 */
Datum
ExecMakeFunctionResultSet(SetExprState *fcache,
						  ExprContext *econtext,
						  MemoryContext argContext,
						  bool *isNull,
						  ExprDoneCond *isDone)
{
	List	   *arguments;
	Datum		result;
	FunctionCallInfo fcinfo;
	PgStat_FunctionCallUsage fcusage;
	ReturnSetInfo rsinfo;
	bool		callit;
	int			i;

restart:

	/* Guard against stack overflow due to overly complex expressions */
	check_stack_depth();

	/*
	 * If a previous call of the function returned a set result in the form of
	 * a tuplestore, continue reading rows from the tuplestore until it's
	 * empty.
	 */
	if (fcache->funcResultStore)
	{
		TupleTableSlot *slot = fcache->funcResultSlot;
		MemoryContext oldContext;
		bool		foundTup;

		/*
		 * Have to make sure tuple in slot lives long enough, otherwise
		 * clearing the slot could end up trying to free something already
		 * freed.
		 */
		oldContext = MemoryContextSwitchTo(slot->tts_mcxt);
		foundTup = tuplestore_gettupleslot(fcache->funcResultStore, true, false,
										   fcache->funcResultSlot);
		MemoryContextSwitchTo(oldContext);

		if (foundTup)
		{
			*isDone = ExprMultipleResult;
			if (fcache->funcReturnsTuple)
			{
				/* We must return the whole tuple as a Datum. */
				*isNull = false;
				return ExecFetchSlotHeapTupleDatum(fcache->funcResultSlot);
			}
			else
			{
				/* Extract the first column and return it as a scalar. */
				return slot_getattr(fcache->funcResultSlot, 1, isNull);
			}
		}
		/* Exhausted the tuplestore, so clean up */
		tuplestore_end(fcache->funcResultStore);