Function MakeTupleTableSlot

src/backend/executor/execTuples.c:1128–1179

-------------------------------- * MakeTupleTableSlot * * Basic routine to make an empty TupleTableSlot of given * TupleTableSlotType. If tupleDesc is specified the slot's descriptor is * fixed for its lifetime, gaining some efficiency. If that's * undesirable, pass NULL. * -------------------------------- */

 * --------------------------------
 */
TupleTableSlot *
MakeTupleTableSlot(TupleDesc tupleDesc,
				   const TupleTableSlotOps *tts_ops)
{
	Size		basesz,
				allocsz;
	TupleTableSlot *slot;

	basesz = tts_ops->base_slot_size;

	/*
	 * When a fixed descriptor is specified, we can reduce overhead by
	 * allocating the entire slot in one go.
	 */
	if (tupleDesc)
		allocsz = MAXALIGN(basesz) +
			MAXALIGN(tupleDesc->natts * sizeof(Datum)) +
			MAXALIGN(tupleDesc->natts * sizeof(bool));
	else
		allocsz = basesz;

	slot = palloc0(allocsz);
	/* const for optimization purposes, OK to modify at allocation time */
	*((const TupleTableSlotOps **) &slot->tts_ops) = tts_ops;
	slot->type = T_TupleTableSlot;
	slot->tts_flags |= TTS_FLAG_EMPTY;
	if (tupleDesc != NULL)
		slot->tts_flags |= TTS_FLAG_FIXED;
	slot->tts_tupleDescriptor = tupleDesc;
	slot->tts_mcxt = CurrentMemoryContext;
	slot->tts_nvalid = 0;

	if (tupleDesc != NULL)
	{
		slot->tts_values = (Datum *)
			(((char *) slot)
			 + MAXALIGN(basesz));
		slot->tts_isnull = (bool *)
			(((char *) slot)
			 + MAXALIGN(basesz)
			 + MAXALIGN(tupleDesc->natts * sizeof(Datum)));

		PinTupleDesc(tupleDesc);
	}

	/*
	 * And allow slot type specific initialization.
	 */
	slot->tts_ops->init(slot);

	return slot;
}

/* --------------------------------
 *		ExecAllocTableSlot