Function AnyTable_GetNextTuple

src/backend/executor/nodeTableFunction.c:499–530

* Get the next tuple from anytable * * will alloc memory in caller's memory context. * caller need to release the memory using pfree() */

 * caller need to release the memory using pfree()
 */
HeapTuple
AnyTable_GetNextTuple(AnyTable t)
{
	MemoryContext oldcontext;
	TupleTableSlot *slot;

	if (t == NULL)
	{
		ereport(ERROR, 
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("invalid null value for anytable type")));
	}

	/* Fetch the next tuple into the tuple slot */
	oldcontext = MemoryContextSwitchTo(t->econtext->ecxt_per_query_memory);
	t->econtext->ecxt_outertuple = ExecProcNode(t->subplan);
	MemoryContextSwitchTo(oldcontext);
	if (TupIsNull(t->econtext->ecxt_outertuple))
	{
		return (HeapTuple) NULL;
	}

	/* ----------------------------------------
	 * 1) Fetch the tuple from the tuple slot
	 * 2) apply resjunk filtering
	 * 3) copy result into a HeapTuple
	 * ----------------------------------------
	 */

	slot = ExecFilterJunk(t->junkfilter, t->econtext->ecxt_outertuple);
	return ExecCopySlotHeapTuple(slot);
}

/*
 * tf_set_userdata_internal