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From <Jan.Mate...@rzf.fin-nrw.de>
Subject AW: Ant 1.7 build, high CPU use, possible solution
Date Tue, 24 Apr 2007 05:03:16 GMT
And Mike,

I invite you to make some performance tests with your project in our next 1.7.1 release phase
;-)


Jan

>-----Urspr√ľngliche Nachricht-----
>Von: Matt Benson [mailto:gudnabrsam@yahoo.com] 
>Gesendet: Dienstag, 24. April 2007 00:45
>An: Ant Users List; m5@works.com
>Betreff: Re: Ant 1.7 build, high CPU use, possible solution
>
>
>--- Mike McNally <m5@works.com> wrote:
>
>> I've been using Ant to build a fairly large web
>> application (about
>> twelve thousand .class files and various other
>> things in a multi-phase
>> build) for several years.  We've generally been
>> pretty happy with Ant
>> performance.  Recently, however, we noticed that if
>> we ran Ant 1.7 on
>> the same build configuration the process was very
>> noticeably slower, and
>> involved long (many seconds) periods of high CPU
>> load.  Through some
>> poking it appeared that the <copy> task was
>> incurring the load, which
>> seemed odd.
>> 
>> So today I ran a build with JMP (Java Memory
>> Profiler) just out of
>> curiosity, after having downloaded and built the
>> source.  At the point
>> of the large copy, I noticed that the "contains"
>> method on
>> java.util.ArrayList was being called very many
>> times, and that that was
>> resulting in a tremendous number of calls to compare
>> Resource instances.
>> 
>
>Hi, Mike--the code in Union in Ant 1.7 is similar to
>that used to cull dupes from Paths in earlier
>versions, except that a Vector was used.  I am
>perfectly willing to believe it might not be as
>clueful as it could be.  What would be great is if you
>could concoct a harmless example build--maybe a
>buildfile that could create whatever structure is
>needed--or at least a description of how to create
>such a structure, that would allow us to run Ant 1.6.5
>and Ant 1.7 and easily see the altered timings,
>attaching to a bug report containing the text of your
>email here.
>
>Thanks,
>Matt
>
>> It seems to me that the code in
>> Union.getCollection() is the culprit.
>> For reasons unknown to me it builds up its result
>> with an obviously n^2
>> loop to avoid duplicates in the result collection. 
>> By experimentally
>> replacing the "ArrayList" with "LinkedHashSet", the
>> excessive CPU load
>> is completely cured.
>> 
>> I realize that there might be some issue using
>> LinkedHashSet, because
>> it's from a fairly recent Java version, but the code
>> could also work by
>> just keeping an explicit java.util.HashSet around in
>> parallel with the
>> ArrayList being assembled.
>> 
>> 
>> 
>> For comparison, a build on an already-built source
>> tree (i.e., something
>> that just runs through the <copy> task without
>> ending up doing anything)
>> takes 15 seconds with my "fixed" Ant 1.7, 45 seconds
>> without the fix,
>> and 15 seconds with Ant 1.6.5.  (My machine is a
>> fairly modern
>> dual-processor P4 with lots of memory, running
>> Linux.)
>> 
>> 
>> (If this is a known and solved problem, my
>> apologies; I can't find any
>> mention of it on the web.)
>> 
>> --
>> [ I love pre-moistened towelettes ] Mike McNally --
>> m5@works.com
>> 
>>
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>
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