mutable-types.clj

(defprotocol Settable
  (set-val! [mutable newval]))

(deftype unsynchronized-raw-box [#^{:unsynchronized-mutable true} val]
  clojure.lang.IDeref
  (deref [] val)

  Settable
  (set-val! [newval] (set! val newval)))

(let [a 1
      b 2
      box (unsynchronized-raw-box a)]
  (dotimes [_ 10]
    (time (dotimes [_ 10000000]
            (set-val! box a)
            (set-val! box b)))))

"Elapsed time: 64.949612 msecs"
"Elapsed time: 33.790096 msecs"
"Elapsed time: 36.375978 msecs"
"Elapsed time: 31.626686 msecs"
"Elapsed time: 31.390412 msecs"
"Elapsed time: 33.930687 msecs"
"Elapsed time: 36.672316 msecs"
"Elapsed time: 33.789399 msecs"
"Elapsed time: 31.617536 msecs"
"Elapsed time: 31.929937 msecs"

(let [a 1
      b 2
      box (atom a)]
  (dotimes [_ 10]
    (time (dotimes [_ 10000000]
            (reset! box a)
            (reset! box b)))))

"Elapsed time: 394.484753 msecs"
"Elapsed time: 387.050261 msecs"
"Elapsed time: 406.516909 msecs"
"Elapsed time: 386.690437 msecs"
"Elapsed time: 349.206909 msecs"
"Elapsed time: 358.410415 msecs"
"Elapsed time: 364.278847 msecs"
"Elapsed time: 360.751779 msecs"
"Elapsed time: 433.286039 msecs"
"Elapsed time: 355.322019 msecs"

(let [a 1
      b 2
      box (clojure.lang.Box. a)]
  (dotimes [_ 10]
    (time (dotimes [_ 10000000]
            (set! (.val box) a)
            (set! (.val box) b)))))

"Elapsed time: 45.705549 msecs"
"Elapsed time: 47.722432 msecs"
"Elapsed time: 30.760789 msecs"
"Elapsed time: 32.69093 msecs"
"Elapsed time: 34.100332 msecs"
"Elapsed time: 31.004816 msecs"
"Elapsed time: 31.849479 msecs"
"Elapsed time: 34.290581 msecs"
"Elapsed time: 30.90627 msecs"
"Elapsed time: 33.529796 msecs"

(defmacro time-without-ret
  "Evaluates expr and prints the time it took.  Returns nil."
  [expr]
  `(let [start# (. System (nanoTime))]
     ~expr
     (prn (str "Elapsed time: " (/ (double (- (. System (nanoTime)) start#)) 1000000.0) " msecs"))))

(deftype Bench [#^{:unsynchronized-mutable true} val]

  Runnable
  (run [] (let [a 1 b 2]
            (set! val a)
            (dotimes [_ 10]
              (time-without-ret (dotimes [_ 10000000]
                                  (set! val a)
                                  (set! val b)))))))

(.run (Bench 1))

"Elapsed time: 29.30358 msecs"
"Elapsed time: 47.739091 msecs"
"Elapsed time: 37.177694 msecs"
"Elapsed time: 41.198596 msecs"
"Elapsed time: 40.169135 msecs"
"Elapsed time: 41.234703 msecs"
"Elapsed time: 39.963732 msecs"
"Elapsed time: 39.991809 msecs"
"Elapsed time: 40.180728 msecs"
"Elapsed time: 40.001725 msecs"