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From "Michael McCandless (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-3841) CloseableThreadLocal does not work well with Tomcat thread pooling
Date Sun, 11 Mar 2012 17:18:59 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-3841?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael McCandless updated LUCENE-3841:
---------------------------------------

    Attachment: LUCENE-3841.patch

Patch.

I cutover to WeakHashMap for the hard refs, and now purge periodically
from both set and get.  The purge frequency is 20X the number of
threads in the map, so that the amortized cost remains linear.

I also stopped using CTL in PagedBytes, and added some additional
tests for it.


                
> CloseableThreadLocal does not work well with Tomcat thread pooling
> ------------------------------------------------------------------
>
>                 Key: LUCENE-3841
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3841
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/other
>    Affects Versions: 3.5
>         Environment: Lucene/Tika/Snowball running in a Tomcat web application
>            Reporter: Matthew Bellew
>            Assignee: Michael McCandless
>             Fix For: 3.6, 4.0
>
>         Attachments: LUCENE-3841.patch
>
>
> We tracked down a large memory leak (effectively a leak anyway) caused
> by how Analyzer users CloseableThreadLocal.
> CloseableThreadLocal.hardRefs holds references to Thread objects as
> keys.  The problem is that it only frees these references in the set()
> method, and SnowballAnalyzer will only call set() when it is used by a
> NEW thread.
> The problem scenario is as follows:
> The server experiences a spike in usage (say by robots or whatever)
> and many threads are created and referenced by
> CloseableThreadLocal.hardRefs.  The server quiesces and lets many of
> these threads expire normally.  Now we have a smaller, but adequate
> thread pool.  So CloseableThreadLocal.set() may not be called by
> SnowBallAnalyzer (via Analyzer) for a _long_ time.  The purge code is
> never called, and these threads along with their thread local storage
> (lucene related or not) is never cleaned up.
> I think calling the purge code in both get() and set() would have
> avoided this problem, but is potentially expensive.  Perhaps using 
> WeakHashMap instead of HashMap may also have helped.  WeakHashMap 
> purges on get() and set().  So this might be an efficient way to
> clean up threads in get(), while set() might do the more expensive
> Map.keySet() iteration.
> Our current work around is to not share SnowBallAnalyzer instances
> among HTTP searcher threads.  We open and close one on every request.
> Thanks,
> Matt

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