function_utils.clj

;; Various Operators on Pure Functions
;;
;; Open source Liscence and all that
(ns 
  
   "Collection of Operators on Pure Functions"
    {:author "Robert McIntyre"}

  mobius.utils.function-utils
  (:use [clojure.contrib.profile]))


(comment

  "Please help me out here.  I'm trying to make a higher order function that takes
   pure functions that are mathmaticaly the same but have different times and returns another
   function that runs them both and returns the resut of the one that finishes first."


  "here's a repl session:

mobius> " (time (dotimes [_ 500]((mix-futures + +) 40 3 3 3 3 3))) "
Elapsed time: 85.792995 msecs
nil
mobius> " (time (dotimes [_ 500](+ 40 3 3 3 3 3))) "
Elapsed time: 6.956338 msecs
nil
mobius> " (time (dotimes [_ 500]((mix-threads + +) 40 3 3 3 3 3))) "
Elapsed time: 706.227065 msecs
nil


mobius> " (defn fast-five [& args] 5) "
#'mobius/fast-five

mobius> " (defn slow-five [& args] (Thread/sleep 5000) (println "Oh YEAH!!!!") 5) "
#'mobius/slow-five

mobius> " (profile (time (dotimes [_ 5000] (thread-five)))) "
\"Elapsed time: 12187.981587 msecs\"
          Name      mean       min       max     count       sum
   create-atom      9621      2025   4433928      5000  48106830
create-threads      5156      2724   2880268      5000  25783796
  kill-threads     91313     27866  11175718      5000  456567066
          loop   2124249     38482  18470781      5000  10621249899
        return      1242       838      5309      5000   6212626
 start-threads    252985    110348  12272835      5000  1264927953
nil

mobius> " (profile (time (dotimes [_ 5000] (future-five)))) "
\"Elapsed time: 607.266671 msecs\"
          Name      mean       min       max     count       sum
   create-atom      1472      1047     31708      5000   7363139
create-futures     30539      2514   1330660      5000  152697998
  kill-threads     54158      2444   3938833      5000  270792897
          loop     81117      8800   6083059      5000  405587516
        return      1215       838    618782      5000   6078146
nil



What can I improve here, and why is the future version sooo much faster than the
thread version? Is there a better way than using loop?
"

)



(defn mix-futures
  " Takes any number mathematically identical pure functions and returns a function 
   that runs each in a separate thread, returns the result from the first thread which finishes,
   and cancels the other threads. Uses futures which are more elegant."

  [& functions]
  (fn [& args]
    (let [result (prof :create-atom (atom ::void))
	  futures (prof :create-futures (doall (map
				 (fn [fun](future
					   (reset! result (apply fun args)))) functions)))]
      
      (prof :loop (loop []
	(if (=  (deref result) void)
	  (recur)
	  (do (prof :future-cancel (dorun (map future-cancel futures)))
	      (prof :return (deref result)))
	  ))))))


(defn mix-threads
  " Takes any number of pure functions that take the same arguments and
   compute the same value and returns a function that runs each in a separate
   thread, returns the result from the first thread which finshes, and cancels 
   the other threads. Explicitly uses nasty Threads.

   For example: 
   (do
   (defn fun1 [] (Thread/sleep 5000) 5)
   (defn fun2 [] (Thread/sleep 700000) 5)
   (time ((mix fun1 fun2))))
   
   Returns: 
    | Elapsed time: 5000.66214 msecs
   5"
  [& functions]
  (fn [& args]
    (let [result (prof :create-atom (atom ::void))
	  threads
	   (prof :create-threads (map 
	   (fn [fun] 
	     (Thread. 
	      (fn [] 
		(try (let [answer (apply fun args)]
		       (reset! result answer))
		     (catch Exception _ nil)))))
	   functions))]
      
      (prof :start-threads (dorun (map #(.start %) threads)))
      (prof :loop (loop []
	(if (=  (deref result) void)
	  (recur)
	  (do (prof :kill-threads (dorun (map #(.stop %) threads)))
	      (prof :return (deref result)))
	  ))))))

(defmacro defmix
  " Defines a function from any number of pure functions that take the same 
   arguments and compute the same value which:

   Runs each in a separate thread.
   Returns the result from the first thread which finshes.
   Cancels the other threads.
           
   Use this whenever you want to combine two pure functions that
   compute the same thing, but use different algorithms with different
   run times for various inputs.

   For example: 
     (do
     (defn fun1 [] (Thread/sleep 5000) 5)
     (defn fun2 [] (Thread/sleep 700000) 5)
     (defmix fun3 \"combination of fun1 and fun2\" fun1 fun2)
     (time (fun3))
   
   Returns: 
     | Elapsed time: 5000.66214 msecs
     5"

{:arglists '([name doc-string? functions*])}

  [name & functions]
  (let [doc-string (if (string? (first functions)) (first functions) "")
	functions (if (string? (first functions)) (rest functions) functions)
	arglists (:arglists (meta (resolve (eval `(quote ~(first functions))))))
	name (with-meta name (assoc (meta name) :arglists `(quote ~arglists) :doc doc-string))]   
    `(def ~name (mix ~@functions))))



;I'm thinking this will be the docstring for mix eventually.

  ;; " Takes any number of pure functions that take the same arguments and
  ;;  compute the same value and returns a function that runs each in a separate
  ;;  thread, returns the result from the first thread which finshes, and cancels 
  ;;  the other threads.

  ;;  For example: 
  ;;  (do
  ;;  (defn fun1 [] (Thread/sleep 5000) 5)
  ;;  (defn fun2 [] (Thread/sleep 700000) 5)
  ;;  (time ((mix fun1 fun2))))
   
  ;;  Returns: 
  ;;   | Elapsed time: 5000.66214 msecs
  ;;  5"