Function assign_simple_var

src/pl/plpgsql/src/pl_exec.c:8397–8459

* assign_simple_var --- assign a new value to any VAR datum. * * This should be the only mechanism for assignment to simple variables, * lest we do the release of the old value incorrectly (not to mention * the detoasting business). */

 * the detoasting business).
 */
static void
assign_simple_var(PLpgSQL_execstate *estate, PLpgSQL_var *var,
				  Datum newvalue, bool isnull, bool freeable)
{
	Assert(var->dtype == PLPGSQL_DTYPE_VAR ||
		   var->dtype == PLPGSQL_DTYPE_PROMISE);

	/*
	 * In non-atomic contexts, we do not want to store TOAST pointers in
	 * variables, because such pointers might become stale after a commit.
	 * Forcibly detoast in such cases.  We don't want to detoast (flatten)
	 * expanded objects, however; those should be OK across a transaction
	 * boundary since they're just memory-resident objects.  (Elsewhere in
	 * this module, operations on expanded records likewise need to request
	 * detoasting of record fields when !estate->atomic.  Expanded arrays are
	 * not a problem since all array entries are always detoasted.)
	 */
	if (!estate->atomic && !isnull && var->datatype->typlen == -1 &&
		VARATT_IS_EXTERNAL_NON_EXPANDED(DatumGetPointer(newvalue)))
	{
		MemoryContext oldcxt;
		Datum		detoasted;

		/*
		 * Do the detoasting in the eval_mcontext to avoid long-term leakage
		 * of whatever memory toast fetching might leak.  Then we have to copy
		 * the detoasted datum to the function's main context, which is a
		 * pain, but there's little choice.
		 */
		oldcxt = MemoryContextSwitchTo(get_eval_mcontext(estate));
		detoasted = PointerGetDatum(detoast_external_attr((struct varlena *) DatumGetPointer(newvalue)));
		MemoryContextSwitchTo(oldcxt);
		/* Now's a good time to not leak the input value if it's freeable */
		if (freeable)
			pfree(DatumGetPointer(newvalue));
		/* Once we copy the value, it's definitely freeable */
		newvalue = datumCopy(detoasted, false, -1);
		freeable = true;
		/* Can't clean up eval_mcontext here, but it'll happen before long */
	}

	/* Free the old value if needed */
	if (var->freeval)
	{
		if (DatumIsReadWriteExpandedObject(var->value,
										   var->isnull,
										   var->datatype->typlen))
			DeleteExpandedObject(var->value);
		else
			pfree(DatumGetPointer(var->value));
	}
	/* Assign new value to datum */
	var->value = newvalue;
	var->isnull = isnull;
	var->freeval = freeable;

	/*
	 * If it's a promise variable, then either we just assigned the promised