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From "Andrew Wilson (JIRA)" <>
Subject [jira] Updated: (LANG-459) Issue in HashCodeBuilder which only shows up under high load multi-threaded usage.
Date Mon, 15 Sep 2008 16:13:44 GMT


Andrew Wilson updated LANG-459:


Here is the simple testcase for this problem.  If you run it with one thread everything is
fine.  If you run it with 1000 it starts blowing up!

> Issue in HashCodeBuilder which only shows up under high load multi-threaded usage.
> ----------------------------------------------------------------------------------
>                 Key: LANG-459
>                 URL:
>             Project: Commons Lang
>          Issue Type: Bug
>    Affects Versions: 2.4
>         Environment: All
>            Reporter: Andrew Wilson
>             Fix For: 3.0, Nightly Builds
>         Attachments:
>   Original Estimate: 0.08h
>  Remaining Estimate: 0.08h
> We found we were having problems with HashCodeBuilder under multi-threaded high load.
> I narrowed this down to the following attached test case.
> When I dug into the code, I found the problem was solved by commenting out the isRegistered
method (though this would break the infinite loop problem).
> ( I did a lot of other digging that I wont bore you with).
> So instead I replaced the HashSet with an ArrayList and just added the object, rather
than the toIdentityHashCodeInteger(object)
> This results in about 5 lines of change.  
> My suspicion is that System.identityHashCode does not return unique values (it is after
all a hashcode method).  The code assumes it will return a unique value and this causes the
problem at high loads.
> The downside is a List vs. a Set, but I believe this is necessary.
> I'd like to submit this fix and have it verified (and perhaps improved).  I am convinced
it is a necessary fix which we have seen show up under high loads.
> Kindest regards, 
> Andrew.

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