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</o:shapelayout></xml><![endif]--></head><body lang=SV link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>Sending this to the Hotspot-GC-dev group as well.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'>/Markus<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Markus Grönlund <br><b>Sent:</b> den 23 juni 2014 17:03<br><b>To:</b> hotspot-runtime-dev; serviceability-dev<br><b>Subject:</b> RFR(S): 8047812: Ensure ClassLoaderDataGraph::classes_unloading_do only delivers klasses from CLDs with non-reclaimed class loader oops<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US>Greetings,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Kindly asking for reviews for the following change:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Bug: <a href="https://bugs.openjdk.java.net/browse/JDK-8047812">https://bugs.openjdk.java.net/browse/JDK-8047812</a><o:p></o:p></span></p><p class=MsoNormal>Webrev: <a href="http://cr.openjdk.java.net/~mgronlun/8047812/webrev01">http://cr.openjdk.java.net/~mgronlun/8047812/webrev01</a> <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-US>Description:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>The "8038212: Method::is_valid_method() check has performance regression <br> impact for stackwalking" - changeset introduced a change in how the ClassLoaderDataGraph::_unloading list of ClassLoaderData's is purged. <br><br>This change to the purging of the CLD’s work the same as before for most GC's, but when using CMS GC, SystemDictionary::do_unloading() is called twice with no explicit purge call in between. On the second call (post-sweep), we can now get stale class loader oops delivered as part of the Klass closure callbacks from the _unloading list. Again, this is because there is no explicit purge call in between these two entries to SystemDictionary::do_unloading() - and being CMS and concurrent, it is very hard to accommodate a timely and proper purge call here.<br><br>The first do_unloading call comes after CMS concurrent marking, and the second comes from a Full GC triggered while sweeping the CMS heap. <br><br>This fix ensures the unloading purge mechanism to work correctly also for the CMS collector, in that only CLDs with non-reclaimed class loader oops will deliver klasses from the _unloading list. In addition, this will ensure a single "logical" pass is achieved when iterating the unloading list in-between purges (avoiding the processing of the same data twice). <br><br>This fix is precipitated by nightly testing failures with CMS after the introduction of 8038212: Method::is_valid_method() check has performance regression <br> impact for stackwalking" - for example "nsk/sysdict/vm/stress/jck12a//sysdictj12a008" which is crashing because of following up stale klass loader oop's from the ClassLoaderDataGraph::_unloading list.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Thanks<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Markus<o:p></o:p></span></p></div></body></html>