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<td style="vertical-align: top;; padding: 0px; border-collapse: collapse; padding-right: 5px; font-size: 20px; line-height: 30px; mso-line-height-rule: exactly" class="page-title-pattern-header-container"> <span class="page-title-pattern-header" style="font-family: Arial, sans-serif; padding: 0; font-size: 20px; line-height: 30px; mso-text-raise: 2px; mso-line-height-rule: exactly; vertical-align: middle"> <a href="https://issues.shibboleth.net/jira/browse/OSJ-328" style="color: #3b73af; text-decoration: none">Re: NPE in IndexedXMLObjectChildrenList</a> </span> </td>
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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0px; border-collapse: collapse; padding: 0 0 10px 0"> <p style="margin: 10px 0 0 0; margin-top: 0">Yes, I think the <tt>checkAndCreateIndex</tt> method is the culprit. Looks like the simple, classic race condition of "if map doesn't contain key, create a new instance and add it". The person who wrote this code like 15 years ago (!!) consistently didn't grok this concurrency idiom, and I constantly had to fix it. Apparently I missed this one.</p> <p style="margin: 10px 0 0 0">I also am surprised that we haven't seen this more, but I guess it's b/c most of our <tt>XMLObject</tt> usage really is single-threaded. The big exception is metadata, as you say, and you have to be doing the <tt>sublist(QName)</tt> case, which I imagine hasn't been common over the years, at least in metadata. Maybe we're seeing it more now because people are starting to actually use extensions more, for entity attributes and metadata-driven config, etc.</p> <p style="margin: 10px 0 0 0">To be fair, <tt>IndexedXMLObjectChildrenList</tt> is actually marked as <tt>@NotThreadSafe</tt>. But that's non-sensical in terms of how it's used. It at least has to be thread-safe for <b>reading</b>, otherwise it doesn't make any sense. Callers of the public methods of <tt>XMLObject</tt> types don't know anything about the internal impl and that they'd need to lock around a simple get(...) call.</p> <p style="margin: 10px 0 0 0">Off-hand I think the simple solution is to just make that method <tt>synchronized</tt>. But I'll think on it and also examine that whole class again.</p> </td>
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