[jboss-jira] [JBoss JIRA] Resolved: (JGRP-876) ConcurrentModificationException during startup of JBoss AS 5.0.0.GA

[Bela Ban (JIRA)]

     [ https://jira.jboss.org/jira/browse/JGRP-876?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bela Ban resolved JGRP-876.
---------------------------

    Resolution: Done


Made 'members' a CopyOnWriteArrayList

> ConcurrentModificationException during startup of JBoss AS 5.0.0.GA
> -------------------------------------------------------------------
>
>                 Key: JGRP-876
>                 URL: https://jira.jboss.org/jira/browse/JGRP-876
>             Project: JGroups
>          Issue Type: Bug
>    Affects Versions: 2.6.7
>         Environment: JBoss AS 5.0.0.GA
>            Reporter: Paul Ferraro
>            Assignee: Bela Ban
>             Fix For: 2.6.8, 2.7
>
>
> I encountered a rare ConcurrentModificationException while starting the all profile of JBoss AS 5.0.0.GA:
> 10:34:45,077 ERROR [AbstractKernelController] Error installing to Start: name=HAPartition state=Create
> org.jgroups.ChannelException: connect() failed
> 	at org.jgroups.JChannel.connect(JChannel.java:374)
> 	at org.jboss.ha.framework.server.ClusterPartition$ChannelConnectTask.run(ClusterPartition.java:167)
> 	at org.jboss.util.threadpool.RunnableTaskWrapper.run(RunnableTaskWrapper.java:147)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
> 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
> 	at java.lang.Thread.run(Thread.java:595)
> Caused by: java.util.ConcurrentModificationException
> 	at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
> 	at java.util.AbstractList$Itr.next(AbstractList.java:420)
> 	at java.util.Collections$UnmodifiableCollection$1.next(Collections.java:1010)
> 	at java.util.AbstractCollection.addAll(AbstractCollection.java:318)
> 	at org.jgroups.protocols.TP.handleDownEvent(TP.java:1575)
> 	at org.jgroups.protocols.TP.down(TP.java:1148)
> 	at org.jgroups.protocols.TP$ProtocolAdapter.down(TP.java:2308)
> 	at org.jgroups.protocols.Discovery.down(Discovery.java:354)
> 	at org.jgroups.protocols.MERGE2.down(MERGE2.java:153)
> 	at org.jgroups.protocols.FD_SOCK.down(FD_SOCK.java:370)
> 	at org.jgroups.protocols.FD.down(FD.java:294)
> 	at org.jgroups.protocols.VERIFY_SUSPECT.down(VERIFY_SUSPECT.java:95)
> 	at org.jgroups.protocols.pbcast.NAKACK.down(NAKACK.java:672)
> 	at org.jgroups.protocols.UNICAST.down(UNICAST.java:462)
> 	at org.jgroups.protocols.pbcast.STABLE.down(STABLE.java:299)
> 	at org.jgroups.protocols.pbcast.GMS.installView(GMS.java:545)
> 	at org.jgroups.protocols.pbcast.GMS.installView(GMS.java:453)
> 	at org.jgroups.protocols.pbcast.ClientGmsImpl.becomeSingletonMember(ClientGmsImpl.java:356)
> 	at org.jgroups.protocols.pbcast.ClientGmsImpl.join(ClientGmsImpl.java:86)
> 	at org.jgroups.protocols.pbcast.ClientGmsImpl.join(ClientGmsImpl.java:39)
> 	at org.jgroups.protocols.pbcast.GMS.down(GMS.java:832)
> 	at org.jgroups.protocols.FC.down(FC.java:430)
> 	at org.jgroups.protocols.FRAG2.down(FRAG2.java:158)
> 	at org.jgroups.protocols.pbcast.STATE_TRANSFER.down(STATE_TRANSFER.java:200)
> 	at org.jgroups.protocols.pbcast.FLUSH.down(FLUSH.java:272)
> 	at org.jgroups.stack.ProtocolStack.down(ProtocolStack.java:475)
> 	at org.jgroups.JChannel.downcall(JChannel.java:1478)
> 	at org.jgroups.JChannel.connect(JChannel.java:370)
> Looking at the source, here are the problematic lines:
> 1573: ProtocolAdapter ad=(ProtocolAdapter)prot;
> 1574: List<Address> tmp=ad.getMembers();
> 1575: members.addAll(tmp);
> Looking now at ProtocolAdapter.getMembers(), I see that it does this:
> public List<Address> getMembers() {
>     return Collections.unmodifiableList(members);
> }
> While Collections.unmodifiableList(...) ensures that the caller of getMembers() cannot modify the list, it can still iterate over it (e.g. line 1575).  The offending mutation code is probably in ProtocolAdapter.down(Event):
> case Event.VIEW_CHANGE:
>     View view=(View)evt.getArg();
>     Vector<Address> tmp=view.getMembers();
>     members.clear();
>     members.addAll(tmp);
>     break;
> There are several ways fix this, including, but not limited to:
> * Make ProtocolAdapter.members volatile, and create a new member list on view change
> * Make ProcotolAdapter.members a CopyOnWriteArrayList

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