> People said you can’t write a financial trading system in a garbage collected language
People have been writing HFT systems in GC languages (Java, OCaml) for a while, and as you mentioned, you need to know when to pause/unpause/prevent collection in the critical section.
This [1] is an excerpt from a talk with Dave Lauer [1], who has done it in Java - it took his system ~40 μs from receiving data to producing market order, and he explains in great detail what amount of work the system had to do. And this was >10 years ago.