geoserver/geoserver — pull request #488 by Konstantin-Surzhin (2014-02-19 18:18:53+00:00)
Title: Geo server http session listener proxy

"This method may contain an instance of double-checked locking. This idiom is not correct according to the semantics of the Java memory model. For more information, see the web page http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html." - findbugs

It seems to me
protected Set listeners()
is used in public class GeoServerHttpSessionListenerProxy
only.
And Where do you use the class GeoServerHttpSessionListenerProxy?