TzTime thread safe?

The implementation of TzTime uses:

class TzTime
   class <<self
        attr_accessor :zone
<snip>

and then recommends doing this:

class ApplicationController < ActionController::Base
  around_filter :set_timezone

  private
    def set_timezone
      TzTime.zone = current_user.time_zone
      yield
      TzTime.reset!
    end
end

Won't this cause problems with concurrent requests for two users with
different timezones?

AFAIK Rails doesn't do concurrent requests.

Rails is not thread safe. Thats why we have to use mongrel_cluster . I
believe Merb IS threaded if you're worried about concurrency. It is
also a lot faster!