While reading the release notes, I was also surprised, that they finally have this kind of multi-threading. I knew about places, but they were kind of inflexible, as you couldn't easily send a lambda in Racket, and serializable-lambda was infectious, so one ended up having to pre-define all logic and at runtime only sending data not functions to other places, which was a shame. One could not really build a thing that distributes work via multiple places with that. Or at least no one managed to do that and no one could tell me how to do it. I hope that with the new concurrency stuff this is now possible, even if it may not be as conceptually clean as places were supposed to be.

Ultimately, multi-threading is one reason, why I mostly used GNU Guile, instead of Racket in recent years. Guile's story of using multiple cores is much more solid, using its futures and possibly fibers via a library. I have used futures, which are backed by a pool of threads underneath, to implement a toy parallelized decision tree algorithm/model, that had linear (or close to) speedup.