How are you running these tests? The "correct" way to benchmark such things
is via a real benchmark framework (such as criterium) then compile your
clojure app to a jar (perhaps via lein uberjar) and finally run it via a
bare java invocation: java -jar my.jar.
Lein for example sometimes uses sub-par JVM settings, trading runtime
performance for startup speed.
Timothy
On Sun, Mar 2, 2014 at 4:59 AM, Luc Prefontaine <lprefonta...@softaddicts.ca
> wrote:
> I cannot agree with this...
> Not at 100% at least.
>
> String manipulations are frequent
> enough to mandate some tuning
> if the need is obvious.
>
> Looks to me that this is the case here.
>
> Other core fns went through rewrites
> to improve performance.
>
> Simplicity has nothing to do with
> internal implementations.
>
> If someone comes up with a better
> implementation while providing
> the same behaviours as the current
> str fn, then it should make it's way
> maybe in clojure.string.
>
> "fast-strings" ? Whatever it may be
> named.
>
> Luc P.
>
> > Core fns should be simple, unsurprising, and general.
> >
> > 'Improving' str may hurt simplicity, make behavior more surprising and
> > unexpected, and less general unless proven otherwise.
> >
> > On Sat, Mar 1, 2014 at 7:02 PM, bob <wee....@gmail.com> wrote:
> >
> > >
> > > Good point, Thanks a lot.
> > >
> > > Shall we improve the str fn in the core lib? From my point of view, the
> > > core fns should be performance sensitive.
> > >
> > >
> > >
> > > On Sunday, March 2, 2014 12:03:21 AM UTC+8, Shantanu Kumar wrote:
> > >>
> > >>
> > >>
> > >> On Saturday, 1 March 2014 15:32:41 UTC+5:30, bob wrote:
> > >>>
> > >>> Case :
> > >>>
> > >>> clojure verison:
> > >>>
> > >>> (time (dotimes [n 10000000] (str n "another word"))) ;; take about
> > >>> 5000msec
> > >>>
> > >>> java version
> > >>>
> > >>> long time = System.nanoTime();
> > >>>
> > >>> for(int i=0 ; i<10000000 ;i++){
> > >>> String a=i+"another word";
> > >>> }
> > >>> System.out.println(System.nanoTime()-time);
> > >>>
> > >>>
> > >>> The java version take about 500 msecs, I thought it might be caused
> by
> > >>> the str implementation which is using string builder, and it might
> not be
> > >>> the best choice in the case of no much string to concat, and then I
> replace
> > >>> "another word" with 5 long strings as the parameter, however no
> surprise.
> > >>>
> > >>> I just wonder what make the difference, or how to find the
> difference.
> > >>>
> > >>
> > >> Others have added useful points to this thread. Java string
> concatenation
> > >> internally uses StringBuilder, so if you replace (str n "another
> word")
> > >> with the following:
> > >>
> > >> (let [sb (StringBuilder.)]
> > >> (.append sb n)
> > >> (.append sb "another word")
> > >> (.toString sb))
> > >>
> > >> ..then the perf improves 1/4 to 1/3. Further, with the following
> tweak:
> > >>
> > >> (let [sb (StringBuilder. 20)] ; because StringBuilder allocates only
> 16
> > >> chars by default on Oracle JRE
> > >> (.append sb n)
> > >> (.append sb "another word")
> > >> (.toString sb))
> > >>
> > >> ..the perf improves from 1/3 to less than 1/2. Here we simply avoid
> > >> double allocation in StringBuilder.
> > >>
> > >> Other things I made sure were:
> > >>
> > >> 1. I used Criterium to measure
> > >> 2. I used `-server` option
> > >> 3. Made sure reflection warning was on
> > >>
> > >> Shantanu
> > >>
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> Luc Prefontaine<lprefonta...@softaddicts.ca> sent by ibisMail!
>
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