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From Christian Kohlschütter (JIRA) <>
Subject [jira] Commented: (LUCENE-1186) [PATCH] Clear ThreadLocal instances in close()
Date Mon, 25 Feb 2008 14:34:51 GMT


Christian Kohlschütter commented on LUCENE-1186:

This issue is rather a prophylactic one -- until now, I have not encountered an OutOfMemoryError
or slowdown etc.

However, I think it is a good practice to release all resources as soon as an object is not
used anymore. For SegmentReader, this is the case when #close() is called. More, as noted
in LUCENE-436, some VMs (also recent ones) indeed seem to have problems when ThreadLocal values
are not released, so I think it is not just a cosmetic issue.

> [PATCH] Clear ThreadLocal instances in close()
> ----------------------------------------------
>                 Key: LUCENE-1186
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>    Affects Versions: 2.3, 2.3.1, 2.4
>         Environment: any
>            Reporter: Christian Kohlschütter
>            Priority: Minor
>         Attachments: LUCENE-1186-SegmentReader.patch
> As already found out in LUCENE-436, there seems to be a garbage collection problem with
ThreadLocals at certain constellations, resulting in an OutOfMemoryError.
> The resolution there was to remove the reference to the ThreadLocal value when calling
the close() method of the affected classes (see FieldsReader and TermInfosReader).
> For Java < 5.0, this can effectively be done by calling threadLocal.set(null); for
Java >= 5.0, we would call threadLocal.remove()
> Analogously, this should be done in *any* class which creates ThreadLocal values
> Right now, two classes of the core API make use of ThreadLocals, but do not properly
remove their references to the ThreadLocal value
> 1. org.apache.lucene.index.SegmentReader
> 2. org.apache.lucene.analysis.Analyzer
> For SegmentReader, I have attached a simple patch.
> For Analyzer, there currently is no patch because Analyzer does not provide a close()
method (future to-do?)

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