Access static constant variable from multiple threads in C

Question

I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated.

I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask.

I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

Answer 1

If you're only reading and not modifying you shouldn't need any locks

Answer 2

If you initialize them on just one thread and then never modify them, it should be ok to read them concurrently from multiple threads without mutexes etc.

Answer 3

I don't know about other architectures, but intel guarantees that all reads are atomic, however, if you do feel like adding some, use something like value = atomic_add(&variable,0);, this will force all writes then add 0 to the value then return the old value, which doesn't get changed