Function rayon::join

pub fn join<A, B, RA, RB>(oper_a: A, oper_b: B) -> (RA, RB) where A: FnOnce() -> RA + Send, B: FnOnce() -> RB + Send, RA: Send, RB: Send

The join function takes two closures and potentially runs them in parallel but is not guaranteed to. However, the call to join incurs low overhead and is much different compared to spawning two separate threads.