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https://issues.apache.org/jira/browse/LOG4J2-1538?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gary Gregory resolved LOG4J2-1538.
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Resolution: Fixed
Fix Version/s: 2.7
Igor,
Thank you for your report and fix.
This was the only place where getFilter() was called more than once from in one
method.
Keep' em coming!
Gary
> Dynamic removal of filter may cause NPE
> ---------------------------------------
>
> Key: LOG4J2-1538
> URL: https://issues.apache.org/jira/browse/LOG4J2-1538
> Project: Log4j 2
> Issue Type: Bug
> Components: Core
> Affects Versions: 2.6.2
> Reporter: Igor Karpov
> Fix For: 2.7
>
> Original Estimate: 1m
> Remaining Estimate: 1m
>
> In my application, I need to add and remove a filter dynamically.
> The problem is, that it occasionally causes NPE because of the subtle bug in
> AppenderControl.isFilteredByAppenderControl:
> {code:java}
> @PerformanceSensitive
> private boolean isFilteredByAppenderControl(LogEvent event) {
> return this.getFilter() != null && Result.DENY ==
> this.getFilter().filter(event);
> }
> {code}
> here, this.getFilter() is called twice.
> getFilter() is defined in superclass, AbstractFilterable:
> private volatile Filter filter;
> so, it's volatile, and in my case, when I dynamically remove the filter it
> becomes null, and in certain cases it happens right between the two calls to
> getFilter().
> The first call to getFilter() returns non-null, so the secand call is
> performed, which returns null and it causes NPE.
> The easy fix for this is not to call getFilter() twice:
> {code:java}
> @PerformanceSensitive
> private boolean isFilteredByAppenderControl(LogEvent event) {
> Filter filter = this.getFilter(); // do not inline, filter is volatile
> return filter != null && Result.DENY == filter.filter(event);
> }
> {code}
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