c++ - How to synchronise threads without using any synchronisation methods?

Question

I was asked in an interview that it is required to print numbers 1 to 3 in a sequential order by 3 threads without using any synchronisation techniques.

I think that we can access the thread id to find out which thread it is and keep a flag associated with this thread in a structure which can be set to true this thread in currently accessing the data.

Interviewer laughed at this idea. So obviously it is wrong.

What can be the way to achieve this task?

Answer 1

Create thread A
Thread A prints '1'
Thread A creates thread B and exits
Thread B prints '2'
Thread B creates thread C and exits
Thread C prints '3' and
exits

No explicit synchro required, prints 1,2,3 in order using three threads, is a totally pointless exercise.