This patches some of the deficiencies in actionpack which allows Rails to be run with concurrent threads.
I've been doing some testing by applying heavy load on a single mongrel that has been patched to obey ActionController::Base.allow_concurrency. It is not production ready as I have seen Route recognition get confused under heavy load, especially if your routes contain the 'default route' (map.connect ':controller/:action/:id'). At the very least this is a good starting point for anyone who wants to see multithreaded rails at some point in the near future.
To enable, add the following to config/environments/production.rb
ActionController::Base.allow_concurrency = true
ActiveRecord::Base.allow_concurrency = true
This does NOT work in development mode (nor does it make sense for it to work in any environment where config.cache_classes = false).
