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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