Use concurrent-ruby

[svenfuchs]

I'm not 100% certain, but my understanding is that Concurrent:: AtomicReference provides what Atomic used to be.

[eric]

Were you running into problems with this? I was trying to not remove 1.8 support unless it was nessesary, and the new concurrent gem doesn't support 1.8.

[svenfuchs]

@eric sorry, totally missed your response before :/

not actual problems, but atomic is deprecated/eol, and not tested against >= 2.3 any more https://github.com/ruby-concurrency/atomic/blob/master/.travis.yml

not a lot of development has happened between late 2014 and today, which seems to indicate that things are pretty stable?

would you consider releasing 1.0.0 from the current version/master (to have something stable enough supported for versions < 1.9.3) and then go to 1.1.0 for removing the deprecated dependency?

[svenfuchs]

forgot to mention that, IIRC, what triggered this on our side were deprecation warnings about constant ::Fixnum is deprecated (would have to verify this though)