I think the remaining overhead of clojure sample code is that operators in
java such as '++' and '<" etc.They are just an instrument of JVM -- iinc
and if_icmpge. But they are both functions in clojure,and they will be
called by invokevirtual instrument.It cost much more performance.
2014-03-01 20:07 GMT+08:00 dennis zhuang <killme2...@gmail.com>:
> I forgot to note hat i test the java sample and clojure sample code with
> the same jvm options '-server'.
>
>
>
> 2014-03-01 20:03 GMT+08:00 dennis zhuang <killme2...@gmail.com>:
>
> The "String a=i+"another word";" is also compiled into using
>> StringBuilder, see the byte code by javap -v:
>>
>> Code:
>> stack=5, locals=5, args_size=1
>> 0: invokestatic #2 // Method
>> java/lang/System.nanoTime:()J
>> 3: lstore_1
>> 4: iconst_0
>> 5: istore_3
>> 6: iload_3
>> 7: ldc #3 // int 10000000
>> 9: if_icmpge 39
>> 12: new #4 // class
>> java/lang/StringBuilder
>> 15: dup
>> 16: invokespecial #5 // Method
>> java/lang/StringBuilder."<init>":()V
>> 19: iload_3
>> 20: invokevirtual #6 // Method
>> java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
>> 23: ldc #7 // String another word
>> 25: invokevirtual #8 // Method
>> java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
>> 28: invokevirtual #9 // Method
>> java/lang/StringBuilder.toString:()Ljava/lang/String;
>> 31: astore 4
>> 33: iinc 3, 1
>> 36: goto 6
>> 39: getstatic #10 // Field
>> java/lang/System.out:Ljava/io/PrintStream;
>> 42: invokestatic #2 // Method
>> java/lang/System.nanoTime:()J
>> 45: lload_1
>> 46: lsub
>> 47: l2d
>> 48: ldc2_w #11 // double 1.0E9d
>> 51: ddiv
>> 52: invokevirtual #13 // Method
>> java/io/PrintStream.println:(D)V
>>
>>
>> I think the performance hotspot in this simple example is the object
>> allocate/gc and function calling overhead.The str function create
>> an anonymous function every time to concat argument strings:
>>
>> (^String [x & ys]
>> ((fn [^StringBuilder sb more]
>> (if more
>> (recur (. sb (append (str (first more)))) (next more))
>> (str sb)))
>> (new StringBuilder (str x)) ys)))
>>
>> And we all know that a function in clojure is a java object allocated in
>> heap.And another overhead is calling the function,it's virtual method.
>>
>> By watching the gc statistics using 'jstat -gcutil <pid> 2000', i found
>> that the clojure sample ran about 670 minor gc,but the java sample is only
>> 120 minor gc.
>>
>> A improved clojure version,it's performance is closed to java sample:
>>
>> user=> (time (dotimes [n 10000000] (-> (StringBuilder.) (.append n)
>> (.append "another word") (.toString))))
>> "Elapsed time: 1009.942 msecs"
>>
>>
>>
>>
>> 2014-03-01 18:02 GMT+08:00 bob <wee....@gmail.com>:
>>
>> 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.
>>>
>>> Thanks
>>>
>>>
>>>
>>> On Saturday, March 1, 2014 1:26:38 PM UTC+8, Shantanu Kumar wrote:
>>>>
>>>> I have seen (and I keep seeing) a ton of Java code that performs
>>>> poorly. Empirically, it's equally easy to write a slow Java app. You always
>>>> need a discerning programmer to get good performance from any
>>>> language/tool.
>>>>
>>>> Numbers like 1/4 or 1/10 can be better discussed in presence of the
>>>> use-cases and perf test cases. Most of the problems you listed can be
>>>> mitigated by `-server` JIT, avoiding reflection, transients, loop-recur,
>>>> arrays, perf libraries and some Java code.
>>>>
>>>> Shantanu
>>>>
>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "Clojure" group.
>>> To post to this group, send email to clojure@googlegroups.com
>>> Note that posts from new members are moderated - please be patient with
>>> your first post.
>>> To unsubscribe from this group, send email to
>>> clojure+unsubscr...@googlegroups.com
>>> For more options, visit this group at
>>> http://groups.google.com/group/clojure?hl=en
>>> ---
>>> You received this message because you are subscribed to the Google
>>> Groups "Clojure" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to clojure+unsubscr...@googlegroups.com.
>>> For more options, visit https://groups.google.com/groups/opt_out.
>>>
>>
>>
>>
>> --
>> 庄晓丹
>> Email: killme2...@gmail.com xzhu...@avos.com
>> Site: http://fnil.net
>> Twitter: @killme2008
>>
>>
>>
>
>
> --
> 庄晓丹
> Email: killme2...@gmail.com xzhu...@avos.com
> Site: http://fnil.net
> Twitter: @killme2008
>
>
>
--
庄晓丹
Email: killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
