semaphore demo

demo.clj

(defn wrap-parallel [f n]
  (let [-sem (new java.util.concurrent.Semaphore (int n))]
    (fn [& args]
      (.acquire -sem)
      (try
        (apply f args)
        (finally
          (.release -sem))))))

(def wrapped
  (wrap-parallel
   (fn [x]
     (let [id (.threadId (Thread/currentThread))]
       (println (format "thread: %s, x: %s" id x))
       (Thread/sleep 2000)))
   2))

(doseq [x (range 16)]
  (future
    (wrapped x)))