Rails 3 ActionView is not thread-safe

Hey,

no, what you are describing would be the worst case scenario if Hash were thread-safe. The only guarantees for example JRuby makes for concurrent modification of Hashes is that you shouldn't be able to segfault JVM.

Otherwise worst-case scenarios right now are IndexOutOfBound exceptions or some threads stuck in an infinite loops resizing corrupted Hash instances. Of course you need to be pretty unlucky to run into these issues, but that's how it is with threads.

I agree with @thedarkone on this one. JRuby's hash implementation requires synchronization around a shared data structure like a hash or array. The worst that can happen in JRuby's case is that we will raise a ConcurrencyError if the hash is modified by two different threads in a short timeframe. Unfortunately, the code is probably not prepared for this possibility and the error may end up blowing up the whole request.

I haven't looked at the code and am not prepared to suggest an alternative. I'd like to think that there's a way to do this without using a mutex around cache accesses, but I'm not sure. At the very least protecting against errors while reading and/or modifying the cache would be a good start.

No, ConcurencyError exception is unfortunately not the worst thing that can happen on JRuby (or on any Ruby VM with real threads for that matter). Modifying non thread-safe data structures in parallel threads is like parsing HTML with regular expressions. I wouldn't be surprised that it's possible to even get it to mix-up key-value pairs (I haven't read the source code, so I might be wrong). My simple testing however showed threads stuck in infinite loops are nothing out of the ordinary.