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https://issues.apache.org/jira/browse/LANG-453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12735682#action_12735682
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Paul Martin commented on LANG-453:
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Can this be reopened? Or should I create a new issue (with a more detailed
explanation and code sample)?
In summary: I've just seen a memory leak caused by the fact that some values
passed to the ToStringBuilder were both lazily calculated and used by hashCode
and equals (meaning that the hashCode changes during the ToStringBuilder call).
This means that ToStringBuilder (actually ToStringStyle) is not able to remove
the object from the ThreadLocal (since the retrieval of the object's property
value has changed the object's hashCode), thus leaking memory.
Strictly speaking, a mutable object can change its hashCode if its values
change, and the documentation for ToStringBuilder does not require that the
object not change in this way.
I've got a few suggestions:
- Don't use a ThreadLocal - just pass around a Map directly.
- Always clear the ThreadLocal at the end of the call.
- Use an IdentityHashMap (though this would not catch dynamically-generated
proxied references to the same object)
- Document restrictions on the objects that can be passed to ToStringBuilder.
Changing the code would also fix otherwise innocuous memory leaks caused by
broken equals and hashCode methods.
I would be happy to provide more information or to work on a patch if required.
> ToStringBuilder can cause serious memory leaks
> ----------------------------------------------
>
> Key: LANG-453
> URL: https://issues.apache.org/jira/browse/LANG-453
> Project: Commons Lang
> Issue Type: Improvement
> Affects Versions: 2.3
> Environment: all
> Reporter: Olaf Tomczak
>
> ToStringBuilder's constructor registers object passed as argument in thread
> local static registry. This causes serious memory problems in applications
> that run for a long time, use thread pooling and process large amount of data
> (e.g. enterprise web applications). Each call to toString method on an object
> causes this object to be practically impossible to garbage collect.
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