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I did not look into deadlock details but it mentions org.netbeans.spi.project.support.LookupProviderSupport$DelegatingLookupImpl so I'm passing it to projs infra.
Created attachment 92485 [details] thread dump and env dump
I get this deadlock almost always (in couple of seconds) after I start casually using Maven based project. I've started Product Version = NetBeans IDE Dev (Build 091211-96442b6aecaf) (#96442b6aecaf) Operating System = Linux version 2.6.24-24-generic running on i386 Java; VM; Vendor = 1.6.0_17; Java HotSpot(TM) Client VM 14.3-b01; Sun Microsystems Inc. Runtime = Java(TM) SE Runtime Environment 1.6.0_17-b04 Java Home = /usr/lib/jvm/java-6-sun-1.6.0.17/jre with fresh userdir and opened Maven project 'equinox-jsf-spring-jdbc-1.7.1' (downloaded from https://equinox.dev.java.net/servlets/ProjectDocumentList?folderID=7074&expandFolder=7074&folderID=0). I wait for scanning to finish and then I for example open applicationContext.xml from Web Pages/WEB-INF folder and using Control+Left-Mouse-Click I opened source of org.appfuse.service.impl.UserManagerImpl. At this stage deadlock may have happened or usually happens in next couple of seconds. If it does not try Ctrl+Shift+1 to focus Java file in project's logical view or right click project node to see project's actions. That always triggers this deadlock for me.
Created attachment 92559 [details] two more deadlock dumps
*** This bug has been marked as a duplicate of bug 178869 ***