When Iterator invalidation is occurred in observer pattern with single process single thread environment

I'm implementing an observer pattern that the subject notifies observers and I knew it has a issue as bellow.

• Issue : iterator for notify() can be invalid, when container for observers like std::vector, std::list is modified on being notified.

But as I think, in single thread single process environment, invalid iterator issue never be happen except in as bellow situation.

• situation 1 : some observers modify observer container when it notified.


• situation 2: loop for notify() modify observer container on being notified.

I know, situation 1,2 make iterator invalid, but I want to know concrete case.

Hope some advice. Thanks.