[jboss-jira] [JBoss JIRA] Created: (JGRP-891) ConcurrentModificationException during JBoss AS 5.0.0.GA startup

[Paul Ferraro (JIRA)]

ConcurrentModificationException during JBoss AS 5.0.0.GA startup
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                 Key: JGRP-891
                 URL: https://jira.jboss.org/jira/browse/JGRP-891
             Project: JGroups
          Issue Type: Bug
    Affects Versions: 2.6.7
            Reporter: Paul Ferraro
            Assignee: Bela Ban


17:31:01,970 ERROR [UDP] failed handling incoming message
java.util.ConcurrentModificationException
	at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:365)
	at java.util.LinkedHashMap$KeyIterator.next(LinkedHashMap.java:376)
	at java.util.AbstractCollection.containsAll(AbstractCollection.java:285)
	at java.util.AbstractSet.equals(AbstractSet.java:76)
	at org.jgroups.protocols.pbcast.STABLE.allVotesReceived(STABLE.java:428)
	at org.jgroups.protocols.pbcast.STABLE.addVote(STABLE.java:423)
	at org.jgroups.protocols.pbcast.STABLE.handleStableMessage(STABLE.java:554)
	at org.jgroups.protocols.pbcast.STABLE.up(STABLE.java:238)
	at org.jgroups.protocols.UNICAST.up(UNICAST.java:299)
	at org.jgroups.protocols.pbcast.NAKACK.handleMessage(NAKACK.java:842)
	at org.jgroups.protocols.pbcast.NAKACK.up(NAKACK.java:705)
	at org.jgroups.protocols.VERIFY_SUSPECT.up(VERIFY_SUSPECT.java:167)
	at org.jgroups.protocols.FD.up(FD.java:284)
	at org.jgroups.protocols.FD_SOCK.up(FD_SOCK.java:308)
	at org.jgroups.protocols.MERGE2.up(MERGE2.java:144)
	at org.jgroups.protocols.Discovery.up(Discovery.java:263)
	at org.jgroups.protocols.PING.up(PING.java:270)
	at org.jgroups.protocols.TP$ProtocolAdapter.up(TP.java:2319)
	at org.jgroups.protocols.TP.passMessageUp(TP.java:1253)
	at org.jgroups.protocols.TP.access$100(TP.java:49)
	at org.jgroups.protocols.TP$IncomingPacket.handleMyMessage(TP.java:1830)
	at org.jgroups.protocols.TP$IncomingPacket.run(TP.java:1809)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
	at java.lang.Thread.run(Thread.java:595)

Here are the problematic lines in STABLE.java:

427:    private boolean allVotesReceived(Set<Address> votes) {
428:        return votes.equals(mbrs); // compares identity, size and element-wise (if needed)
429:    }

Internally, the Set.equals(...) method will iterate over the mbrs set.
The concurrent update is coming from the following code in STABLE.java:

330:    private void handleViewChange(View v) {
331:        Vector<Address> tmp=v.getMembers();
332:        synchronized(mbrs) {
333:            mbrs.clear();
334:            mbrs.addAll(tmp);
335:        }

There are several ways fix this, including, but not limited to:

* Wrap line 428 in a synchronized(mbrs) block

* Make mbrs volatile instead of final, and create a new LinkedHashSet in handleViewChange(...)
i.e.  Replace 332-335 with:
mbrs = new LinkedHashSet<Address>(tmp);

* Make mbrs a CopyOnWriteArraySet<Address>

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