Benchmark between HashMap with lock vs. persistent map with atom

gistfile1.clj

(defn map-incr-unsafe []
  (let [m (java.util.HashMap.)]
	  (.put m "a" 0)
	  (doseq [i (range 1000000)]
	    (let [a (.get m "a")]
		  (.put m "a" (inc a))
		  ))))

(defn map-incr-safe []
  (let [o (Object.)
        m (java.util.HashMap.)]
	  (.put m "a" 0)
	  (doseq [i (range 1000000)]
	    (locking o
	      (let [a (.get m "a")]
		    (.put m "a" (inc a))
		    )))))

(defn map-incr-atom []
  (let [m (atom {"a" 0})]
	  (doseq [i (range 1000000)]
	    (swap! m (fn [m] (assoc m "a" (inc (m "a")))))
	    )))

user> (time (map-incr-unsafe))
"Elapsed time: 49.981 msecs"

user> (time (map-incr-safe))
"Elapsed time: 190.859 msecs"

user> (time (map-incr-atom))
"Elapsed time: 101.537 msecs"