Do I need to use locking with integers in c++ threads

Question

If I am accessing a single integer type (e.g. long, int, bool, etc...) in multiple threads, do I need to use a synchronisation mechanism such as a mutex to lock them. My un

Answer 1

Multithreading is hard and complex. The number of hard to diagnose problems that can come around is quite big. In particular, on intel architectures reads and writes from aligned 32bit integers is guaranteed to be atomic in the processor, but that does not mean that it is safe to do so in multithreaded environments.

Without proper guards, the compiler and/or the processor can reorder the instructions in your block of code. It can cache variables in registers and they will not be visible in other threads...

Locking is expensive, and there are different implementations of lock-less data structures to optimize for high performance, but it is hard to do it correctly. And the problem is a that concurrency bugs are usually obscure and difficult to debug.