Add synchronization around use of @cluster and other variables Fix #332

[hydrogen18]

This class has the correct primitives to be thread safe, but it was missing a synchronize block.
Fix #332

[pezra]

Please rebase and i'll merge this.

[hydrogen18]

This has no conflicts now.

[pezra]

Thanks for the improvement.

[bernardobarreto]

Hi @pezra, @hydrogen18.
Could you guys, explain why I'm getting this error sometimes and what does it mean?:

Thanks in advance.

[pezra]

@bernardofire, that is pretty interesting. Given the if defined? @cluster guard it implies that multiple threads are running this method at the same time. Cequel is not thread safe, though we are working in that direction. Are you running this in a multi-threaded setup?

[lxbrito]

Hi @pezra,
@bernardofire asked me to answer you. Yes, definitely. We are running some instances of Sidekiq with 12 threads each. Do you think that doubling the sidekiq instances while halving the thread count would make us see less @cluster errors?

[pezra]

I suspect you would see less of that issue with more processes and fewer threads.

Another option would be to submit a PR to convert that variable into a thread variable or synchronize access to that variable. I would love to get Cequel fully thread safe. If you choose this route I will do everything i can to support your effort.

[hydrogen18]

@lxbrito @bernardofire You're using 2.0.2 which does not contain the fix for this issue, upgrade to 2.0.3

[lxbrito]

@hydrogen18 Do you mean git master? I couldn't find 2.0.3 release.

[pezra]

I haven't released 2.0.3 yet. I am getting a couple more tiny PRs in. It should be out today.

[pezra]

Released in 2.0.3. Thanks, again, for the improvement.