How to make subprocesses wait for join right after start in python?

Question

Python

I need to process a certain array of data:
{ item1: [str, str, str], item2: ... , ... }
Before passing to the values ​​in item2, the algorithm must process and save the data where it should be, and only then proceed to processing data in item2.
In each thread, str is just processed.
I think that I have a race and before the join is executed, the algorithm runs away to item2.
How is it guaranteed to make the entire group of child threads wait for join (which, as I understand it, is needed to make the algorithm in the parent process wait for the child processes to complete)?

Answer 1

Use some kind of synchronization primitive. barrier, for example.