Fixes can't add a new key into hash during iteration error

[ankane]

This adds thread-safety to the MemoryStore. Here's code to reproduce the current issue.

Thread.abort_on_exception = true

$store = Makara::Cache::MemoryStore.new

workers = 10.times.map do
  Thread.new do
    loop do
      $store.write(rand(100), true, expires_in: 1)
      sleep(rand / 100)
    end
  end
end

workers.map(&:join)

[bleonard]

Thanks @ankane - Think you could add the test case to the cache_spec?

[ankane]

Hey @bleonard, thanks for the response. Added a test case.

[bleonard]

@ankane - I've added you as a member if you'd like to participate with makara. Seems like a good idea if you are depending on it.

If so, want to test out master and tag a new release, etc?

[ankane]

Yeah, happy to help out. I'll defer to you on when to release new versions. We'll try to get on master in the near future.

[ankane]

Hey @bleonard, looks like I was invited to join org rather than this specific project.

[bleonard]

It was a team that was only on makara projects. Now given project access if that's better for you.

[ankane]

Ah, gotcha. All good now. Thanks.

[bleonard]

Interesting that Ruby 2 is freaking out (no log) on Travis. https://travis-ci.org/taskrabbit/makara/builds/280541383

Some sort of Mutex or thread difference?

[ankane]

That's odd. Can you try restarting the jobs?

[bleonard]

Actually the nextval one (#173) failed first all in Ruby 2. Then this one, so likely not this one. Likely not that one either based on it's simplicity.

[bleonard]

https://travis-ci.org/taskrabbit/makara/jobs/280541385 bundler failing to install in that ruby. tried similar setup locally and it worked.

[ankane]

@bleonard fixed in #176