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https://issues.apache.org/jira/browse/LOG4J2-1142?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14940632#comment-14940632
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Remko Popma commented on LOG4J2-1142:
-------------------------------------
I confirmed (in Tomcat 7.0.50) that it made no difference whether the
ThreadLocal field static or non-static in AbstractStringLayout; both generated
the warning
{quote}
SEVERE: The web application [/threadlocal] created a ThreadLocal with key of
type [org.apache.logging.log4j.core.layout.AbstractStringLayout$1] (value
[org.apache.logging.log4j.core.layout.AbstractStringLayout$1@5339ea5b]) and a
value of type [java.lang.StringBuilder] (value []) but failed to remove it when
the web application was stopped. Threads are going to be renewed over time to
try and avoid a probable memory leak.
{quote}
The warning goes away if we avoid creating an inner class, so instead of this:
{code}
// tomcat generates warning
protected static final ThreadLocal<StringBuilder> strBuilder = new
ThreadLocal<StringBuilder>(){
@Override
protected StringBuilder initialValue() {
return new StringBuilder(DEFAULT_STRING_BUILDER_SIZE);
}
};
{code}
Use this:
{code}
// no warning
protected static final ThreadLocal<StringBuilder> strBuilder = new
ThreadLocal<StringBuilder>();
{code}
I will look at the pool next.
> ThreadLocals in Layout implementations should be non-static to prevent memory
> leaks in web containers
> -----------------------------------------------------------------------------------------------------
>
> Key: LOG4J2-1142
> URL: https://issues.apache.org/jira/browse/LOG4J2-1142
> Project: Log4j 2
> Issue Type: Improvement
> Components: Layouts
> Affects Versions: 2.4
> Reporter: Dmitri Blinov
> Assignee: Remko Popma
> Fix For: 2.4.1
>
> Attachments: LOG4J2-1142.patch
>
>
> As discussed in LOG4J2-1125, storing ThreadLocal<StringBuilder> in a static
> field may not interact well with the thread pools and class loaders of some
> web containers and may result in memory leaks, especially in older web
> containers.
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