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https://issues.apache.org/jira/browse/MAHOUT-1345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13830981#comment-13830981
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Dawid Weiss commented on MAHOUT-1345:
-------------------------------------
Frank, this means a thread was created in the scope of a test (or suite -- this
is configurable) and then wasn't cleaned up properly. The problem with thread
pools is that they use unnamed threads by default ("pool-154-thread-1"); if
possible it's always best to use a custom thread factory that names threads so
that they can be tracked back to their source (the pool that generates them).
In certain cases thread pools can be shut down and not wait for the forked
threads to perish. There is little one can do about it but wait -- there is an
annotation in rr that does just that (@@ThreadLeakLingering(linger = 2000)).
If you're looking for some advanced scenarios take a look at Lucene source code
(LuceneTestCase class).
> Enable randomised testing for all Mahout modules
> ------------------------------------------------
>
> Key: MAHOUT-1345
> URL: https://issues.apache.org/jira/browse/MAHOUT-1345
> Project: Mahout
> Issue Type: Improvement
> Affects Versions: 0.8
> Reporter: Isabel Drost-Fromm
> Priority: Minor
> Fix For: 0.9
>
> Attachments: MAHOUT-1345.diff, MAHOUT-1345.patch
>
>
> When enabling randomised testing for all modules I found a few tests became
> unstable or even fail deterministically due to lingering threads. The
> attached patch:
> * defines the randomised testing dependency in our parent pom
> * re-uses said dependencies in all depending modules (makes upgrading easier
> as the version number needs to be changed in just one place)
> * adds several code changes that fixed the failures due to lingering threads
> for me on my machine. I'd greatly appreciate input a) from those who wrote
> the respective code and b) others who ran the tests with these changes to
> make sure there are no other tests that suffer from the same issues.
> Warning: I touched quite a few bits and pieces I'm not intimately familiar
> with over the last few weeks (whenever I had a few spare minutes) - second
> pair of eyes needed.
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