I use Common Lisp and Scheme at work, and have written and maintained several systems heavily relied on class redefinition and run-time code loading. They're g

I use Common Lisp and Scheme at work, and have written and maintained several systems heavily relied on class redefinition and run-time code loading. They're great. OTOH, I feel Common Lisp's concurrent process handling is rather weak, and I envy Erlang for that (Not that CL can't do the trick, but usually what implementations offer is fairly low-level and I had to roll my own higher-level IPC.) For example, how well CL's class redefintion and instance reinitialization work with preemptive threads? It isn't obvious how each implementation address this issue by skimming docs, so I'm curious if anybody with direct experience. When I implemented CLOS/MOP style OO in my Scheme, I ended up using a global lock during class redefinition, for it need to modify lots of places. It's MT-safe now, but I'm still wary to run class redefinition on a system written in my Scheme, which is busy handling requests.