Rayon multiple par_iter one after the other

I was wondering how rayon handles multiple parallel iterators one after the other, just to clarify:

vec1.par_iter()...;
vec2.par_iter()...;
vec3.par_iter()...;

Are new threads being launched everytime?, and if so, is there a way to tell rayon to maintain a thread pool on standby without having to resort to other methods in order to do work in parallel? (i.e. I would prefer to retain the simple syntax of several parallel iterators)

Rayon does keep a global thread pool, initialized on first use.

That's perfect!, Thanks for the quick response