Question

I have several threads running concurrently and each of them must generate random numbers. I want to understand if there is a pattern to follow, to understand if it is correct to initialize the random generator with srand in the main thread or if every thread must initialize its own random generator. It seems that rand/srand have not been designed to be used with threads and I’m wondering how I can deal with threads and random numbers together.
Thanks

EDIT: I need pure random numbers, but I’m also interested in generating a deterministic sequence for testing purposes. I’m on linux, but I prefer to write code as portable as possible.

Answer 1

On Linux you can use the rand_r() for a mediocre generator or the drand48_r() function for a much better one. Both are thread safe replacements for rand() and drand48(), by taking a single argument consisting of the current state, instead of using global state.

With regard to your question on initialization, both of the generators above allow you to seed at whatever point you desire, so you are not forced to seed them before spawning your threads.