In a vanilla Rails 3 app, which objects are not thread safe i.e. have serialized access?

In a generic Rails 3 application that uses mysql, what parts of the framework are not t开发者_如何学编程hread safe?

I belief the actual sql connection to the database is serialized? If not that I guess I read something incorrectly.

What areas are not thread safe? Or rather are global references that all requests might share?

All of Rails has been thread safe ever since the 2.2.2 release.