title: What is Clojure volatile?
body: <p>There has been an addition in the recent Clojure 1.7 release : <a href="http://clojuredocs.org/clojure.core/volatile!">volatile!</a></p>
  
  <p><code>volatile</code> is already used in many languages, including java, but what are the semantics in Clojure?</p>
  
  <p>What does it do? When is it useful?</p>