My understanding was that if the ruby VM has parallel threads running and dynamic class definition/alteration is occurring, that is VM-wide and therefore the threads can collide and screw each other up. Zed Shaw wrote the following in “Katana Suicide Concurrency” on Jun 5 2006. “I resisted doing this, but it’s going to come down sooner or later now that François SIMOND figured it out. Mongrel was