Igor Karpov created LOG4J2-1538:
-----------------------------------
Summary: dynamic addition 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
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:
@PerformanceSensitive
private boolean isFilteredByAppenderControl(LogEvent event) {
return this.getFilter() != null && Result.DENY ==
this.getFilter().filter(event);
}
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:
@PerformanceSensitive
private boolean isFilteredByAppenderControl(LogEvent event) {
Filter filter = this.getFilter(); // do not inline, filter is volatile
return filter != null && Result.DENY == filter.filter(event);
}
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