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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 39612] New: - Sudden Nullpointerexception in LRUCache
Date Thu, 18 May 2006 17:12:56 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=39612

           Summary: Sudden Nullpointerexception in LRUCache
           Product: Taglibs
           Version: 1.2.0
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: critical
          Priority: P2
         Component: Cache  Taglib
        AssignedTo: taglibs-dev@jakarta.apache.org
        ReportedBy: silentcrooner@gmail.com


After running the Cache Taglib successfully in a JBoss 4.x.x environment for
many months, I have suddenly experienced a very nasty NullpointerException on
the frontpage of our high volume site, where the tag is used to cache dynamic
list contents in session scope. 

I have not configured the tag using a CacheUtil class but using the default
parameters.

This happened for all users/sessions requesting the front page.

An immediate restart of JBoss solved the issue - but obviously this is highly
worrying. 

I have scoured bugzilla and tried to Google for something similar from CacheTag
users to no avail.

Looking into the LRUCache class and comparing to my stack trace it seems that in
same strange scenario the key can be null, but still return valid entries from
the cache. A NullPointerException then occurs when trying to update the LRU list
in the noteUsed method afterwords.

18:12:53,755 ERROR [Engine] StandardWrapperValve[jsp]: Servlet.service() for ser
                                                                            vlet
jsp threw exception
java.lang.NullPointerException
        at java.util.LinkedList.remove(LinkedList.java:220)
        at org.apache.taglibs.cache.LRUCache.noteUsed(LRUCache.java:199)
        at org.apache.taglibs.cache.LRUCache.get(LRUCache.java:115)
        at org.apache.taglibs.cache.CacheTag.doStartTag(CacheTag.java:49)
        at org.apache.jsp.index_jsp._jspService(index_jsp.java:528)

Could this be a threading issue or what?

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