Add random number generation to Runtime

[schreter]

Currently, openraft is using rand crate to generate random numbers and more concretely, the thread_rng().

Unfortunately, this allocates at suboptimal times, which prevents us from hardening openraft in our project.

The thread-local random number generator query (and its type) should be added to the runtime interface and implemented by default using rand crate.

Alternatively, the random number generator should be created in the local state and not in TLS, which would work as well.

Background: TLS with destructors allocate an entry for running the destructor at thread exit in a vector. This allocation cannot be properly masked in our accounting and we get random extra allocation and/or deallocation accounted making memory leak tests fail.

[github-actions]

👋 Thanks for opening this issue!

Get help or engage by:

• /help : to print help messages.
• /assignme : to assign this issue to you.

[drmingdrmer]

thread_rng() is only used once in the codebase, when Engine is created. It is called only upon startup. Does it affect the performance?

https://github.com/datafuselabs/openraft/blob/1e062d6d0b4b61f284d42936a56858bfccd839c0/openraft/src/engine/engine_config.rs#L45

[schreter]

Does it affect the performance?

No, it's not about performance. It's about the ability to run malfunction and correctness tests of the code.

You don't have to do anything here, I'll take care of it. Just a heads-up.

Maybe I'll do a work-around in our code by instantiating the thread generator manually in the test framework.

BTW, shouldn't it use a newly-generated random number for each election?

[drmingdrmer]

OK I see.

BTW, shouldn't it use a newly-generated random number for each election?

I'm not sure if it is necessary. At my POV, a random timeout for each node instead of for each round is good enough.
Do not know how to prove that 🤔

[schreter]

Completed by #995