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From Mark Thomas <>
Subject Re: Threadlocal problem
Date Tue, 02 Feb 2010 13:44:55 GMT
On 02/02/2010 13:31, Malcolm Warren wrote:
> SEVERE: A web application created a ThreadLocal with key of type
> [org.apache.commons.lang.builder.ToStringStyle$1] (value
> [org.apache.commons.lang.builder.ToStringStyle$1@66a37d72]) and a value
> of type [java.util.HashSet] (value [[]]) but failed to remove it when
> the web application was stopped. To prevent a memory leak, the
> ThreadLocal has been forcibly removed.
> I get this message with every hot redeploy, which is a little worrying.
> Anybody know what it's about?

The message says it all. Something created a ThreadLocal but didn't
clean it up. Tomcat cleaned it up to prevent a memory leak.

> This started with the latest Tomcat 6 version: 6.0.24.
> I'm pleased with this new version because it also pointed out politely
> that I hadn't closed a thread I'd opened.

This is all part of the new memory leak protection added for 6.0.24. It
is good to hear that people are finding it useful.

> I've fixed my Thread but I still get the message shown at the beginning
> of this email.
> I don't use ThreadLocal in my code at all, so it's Tomcat who's creating
> this ThreadLocal for some reason, but since it's not mine it's something
> I can't do much about, presumably.

It isn't Tomcat's (Tomcat doesn't ship with commons-lang) so I am pretty
sure it is yours. Chances are it isn't something you are doing directly
but maybe something a library you are using is doing?

If a library is adding a ThreadLocal to a request processing thread it
*must* remove it before the request completes to avoid a potential
memory leak. If it doesn't, I would argue that is a bug in the library.
At a stretch, if the library provides a mechanism to clean these up on
web app shutdown that is just about OK but that could would need to be
carefully coded.


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