infinitered/cdq — pull request #45 by katsuyoshi (2014-08-12 15:18:10+00:00)
Title: add test for multi threading.

It seems to need to pass a parent context between threads.

The current context is nil when initializing context in the gcd concurrent queue.
Then it create a store in the gcd concurrent queue and rise exception or etc..

Adding a parent argument seems to work.
```def new(concurrency_type, parent = nil, &block)```