[Rails] Is active record 3.1.1 supposed to be threadsafe?

Hi There

Is active record 3.1.1 supposed to be threadsafe?
In other words, should the following (concurrent access to a model)
work?

Thread.new do MyModel.where(some_condition).first end
Thread.new do MyModel.where(some_condition).first end

I ask because upon the answer, it depends which component should handle
synchronization, and in consequence, which component to patch/fix.

A bit of background: We stumbled over a concurrency issue when using
capybara-webkit with rails3.1. We traced the issue down to one thread
querying and trying to accessing the cache while another thread cleared
the same cache.
Assuming active record 3.1.1 is supposed to be threadsafe, then the
culprit for the issue would be
ActiveRecord::ConnectionAdapters::QueryCache, which doesn't synchronize
access to its @query_cache. See
https://github.com/awd-switzerland/rails/commit/22aeda0f0553fdcabca156012b67f2aa2add293c
for a possible way to resolve that. However, I'm not sure in which layer
the rails team wants to handle synchronization.
Also notice that the patch is naive in that it simply assumes thread
support in ruby to be enabled.

Best regards
Stefan Rusterholz

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