fun-with-future.clj

(defn polling [fun]                                                            
  (println "[polling] started")                                                
  (loop []                                                                     
    (if (not (realized? fun))                                                  
      (recur)))                                                                
  (println "[polling] result: " (deref fun))                                   
  (println "[polling] end")                                                    
  (deref fun))                                                                 
                                                                               
(do                                                                            
  (println "[Main] calculus")                                                  
  (def what-is-the-answer                                                      
    (future                                                                    
      (println "[Future] started")                                             
      (Thread/sleep 10000)                                                     
      (println "[Future] completed")                                           
      42))                                                                     
                                                                               
  (def answer-in-future                                                        
    (future                                                                    
      (println "[Future2] started")                                            
      (polling what-is-the-answer)                                             
      (println "[Future2] completed")                                          
      @what-is-the-answer))                                                    
                                                                               
  (println "[Main] created future")                                            
  (println "[Main] do other things, waiting for answer")                       
  (Thread/sleep 1000)                                                          
  (println "[Main] get the answer")                                            
  (println "[Main] result: " @what-is-the-answer)                              
  (println "[Main] get answer2")                                               
  (println "[Main] result: " @answer-in-future)                                
  (println "[Main] shutdown agents")                                           
  (shutdown-agents)                                                            
  (println "[Main] @what-is" @what-is-the-answer)                              
  (println "[Main] end"))