non-blocking example

[codefromthecrypt]

Hi, your code looks neat.

This might not end up being a change here, but in our zipkin library we are working on a non-blocking rate limited implementation of sampling. For example, it returns true 1 time per second. I'm not sure if you have ambition for non-blocking. Also, we couldn't make a strict dependency, but it would be neat to get your input anyway. openzipkin/brave#819

[cap5lut]

For the moment I do not plan to implement a non-blocking way. Plan for now was just to get rid of the busy wait in the blocking method and refactoring the state stuff to create less instance.

But once I'm going to think about that, I will give you a note.

[codefromthecrypt]

thanks very much. incidentally, our server is also looking for a rate limiter solution :P openzipkin/zipkin#2169

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