Thread-safety in a rails app

I've been hearing a lot about thread safety lately in Ruby. My question is, how do I determine whether or not my rails app (actually the open source project refinerycms开发者_StackOverflow) is thread safe or not?

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There is no easy way to determine whether the application is thread-sage or not.

But if there are class variables, Threads are used then it is very likely that the app is not because it requires proper synchronization (which many developers just ignore).

Additionally, the question is impossible to objectively answer because you are concerned about thread-safety in Ruby, but asking about a particular application which are totally different things.