Function ExecAggPlainTransByRef

src/backend/executor/execExprInterp.c:4553–4604

implementation of transition function invocation for byref types */

/* implementation of transition function invocation for byref types */
static pg_attribute_always_inline void
ExecAggPlainTransByRef(AggState *aggstate, AggStatePerTrans pertrans,
					   AggStatePerGroup pergroup,
					   ExprContext *aggcontext, int setno)
{
	FunctionCallInfo fcinfo = pertrans->transfn_fcinfo;
	MemoryContext oldContext;
	Datum		newVal;

	/* cf. select_current_set() */
	aggstate->curaggcontext = aggcontext;
	aggstate->current_set = setno;

	/* set up aggstate->curpertrans for AggGetAggref() */
	aggstate->curpertrans = pertrans;

	/* invoke transition function in per-tuple context */
	oldContext = MemoryContextSwitchTo(aggstate->tmpcontext->ecxt_per_tuple_memory);

	fcinfo->args[0].value = pergroup->transValue;
	fcinfo->args[0].isnull = pergroup->transValueIsNull;
	fcinfo->isnull = false;		/* just in case transfn doesn't set it */

	newVal = FunctionCallInvoke(fcinfo);

	/*
	 * For pass-by-ref datatype, must copy the new value into aggcontext and
	 * free the prior transValue.  But if transfn returned a pointer to its
	 * first input, we don't need to do anything.  Also, if transfn returned a
	 * pointer to a R/W expanded object that is already a child of the
	 * aggcontext, assume we can adopt that value without copying it.
	 *
	 * It's safe to compare newVal with pergroup->transValue without regard
	 * for either being NULL, because ExecAggTransReparent() takes care to set
	 * transValue to 0 when NULL. Otherwise we could end up accidentally not
	 * reparenting, when the transValue has the same numerical value as
	 * newValue, despite being NULL.  This is a somewhat hot path, making it
	 * undesirable to instead solve this with another branch for the common
	 * case of the transition function returning its (modified) input
	 * argument.
	 */
	if (DatumGetPointer(newVal) != DatumGetPointer(pergroup->transValue))
		newVal = ExecAggTransReparent(aggstate, pertrans,
									  newVal, fcinfo->isnull,
									  pergroup->transValue,
									  pergroup->transValueIsNull);

	pergroup->transValue = newVal;
	pergroup->transValueIsNull = fcinfo->isnull;

	MemoryContextSwitchTo(oldContext);
}