Need of thread local

Question

Hi

I have global variable gi. Each thread tries to access and may result a data race. So value could be 3 or lesser at the end.

I do have then atomic and it is thread safe. So value at the end will be 3 for sure.

Now , confustion is for thread local. As it is per thread each thread will be having own variable. So, value will be 1 only.

Here comes my question as I am confused on thread local. If it is needed per thread, we can have it as function stack variable inside function body. It will also be same thing. So, whats the use of thread local ?
https://code.sololearn.com/cay35570Md57/?ref=app

Answer 1

In your perticular case, it won't matter if the variable was thread_local or a local variable inside function.
You would see the difference when your thread calls a function which inturn calls display() function multiple times.

Answer 2

Why gi will always be 3 ? If so, we would never need mutex or any locking mechanism...isn't it or i am missing something ?

Answer 3

Thanks Arsenic .. sounds good...facing hard time to think of some example

Answer 4

FYI in your code gi will always be 3 by the end

Answer 5

Locking is very usefu…but in your example your calling the same function so after the 3 joins you basically did a for loop

Answer 6

Raul Ramirez , could not agree more. I still feel that gi can be mismanipulated without lock..isnt it ?