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https://issues.apache.org/jira/browse/AMQ-3276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13017640#comment-13017640
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Daniel Kulp commented on AMQ-3276:
----------------------------------


Just a note that while testing CXF with 5.5.0, I also run into this 
occasionally.   The CXF test suite will need to remain on 5.4.2 for now.

> ConcurrentModificationException in embedded 5.5.0 broker
> --------------------------------------------------------
>
>                 Key: AMQ-3276
>                 URL: https://issues.apache.org/jira/browse/AMQ-3276
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.5.0
>         Environment: jdk 1.6.0_24, Spring 3.0.5, ActiveMQ 5.5.0, Camel 2.7.0, 
> slf4j 1.6.1
>            Reporter: Dan Checkoway
>            Assignee: Gary Tully
>             Fix For: 5.6.0
>
>
> We just migrated from ActiveMQ 5.4.2 to ActiveMQ 5.5.0.  So far so good, with 
> one exception (pun not intended).  In one case where we have an embedded 
> broker, we're seeing this exception get logged on occasion:
> WARNING; 08-Apr-2011 11:11:41; tid:45931; TransportConnection stopAsync; 
> cannot create async transport stopper thread.. not waiting for stop to 
> complete, reason:
> java.util.ConcurrentModificationException
>         at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
>         at java.util.HashMap$EntryIterator.next(HashMap.java:834)
>         at java.util.HashMap$EntryIterator.next(HashMap.java:832)
>         at java.util.HashMap.putAllForCreate(HashMap.java:435)
>         at java.util.HashMap.<init>(HashMap.java:225)
>         at 
> org.slf4j.helpers.BasicMDCAdapter.getCopyOfContextMap(BasicMDCAdapter.java:130)
>         at org.slf4j.MDC.getCopyOfContextMap(MDC.java:182)
>         at 
> org.apache.activemq.util.MDCHelper.getCopyOfContextMap(MDCHelper.java:30)
>         at 
> org.apache.activemq.broker.TransportConnection.stopAsync(TransportConnection.java:946)
>         at 
> org.apache.activemq.broker.TransportConnection.processShutdown(TransportConnection.java:353)
>         at 
> org.apache.activemq.command.ShutdownInfo.visit(ShutdownInfo.java:35)
>         at 
> org.apache.activemq.broker.TransportConnection.service(TransportConnection.java:306)
>         at 
> org.apache.activemq.broker.TransportConnection$1.onCommand(TransportConnection.java:179)
>         at 
> org.apache.activemq.transport.ResponseCorrelator.onCommand(ResponseCorrelator.java:116)
>         at 
> org.apache.activemq.transport.TransportFilter.onCommand(TransportFilter.java:69)
>         at 
> org.apache.activemq.transport.vm.VMTransport.iterate(VMTransport.java:218)
>         at 
> org.apache.activemq.thread.PooledTaskRunner.runTask(PooledTaskRunner.java:127)
>         at 
> org.apache.activemq.thread.PooledTaskRunner$1.run(PooledTaskRunner.java:48)
>         at 
> java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
>         at 
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
>         at java.lang.Thread.run(Thread.java:662)
> Up until this morning, I had only seen that logged during shutdown of the app 
> context.  But just now, it popped out independently, out of the blue.
> For what it's worth, here's the app context config:
>  
>   <broker xmlns="http://activemq.apache.org/schema/core";
>           id="embeddedActivemqBroker"
>           useJmx="true"
>           persistent="true"
>           schedulerSupport="false"
>           advisorySupport="false"
>           enableStatistics="true">
>     <destinationPolicy>
>       <policyMap>
>         <policyEntries>
>           <policyEntry queue=">" producerFlowControl="false" 
> memoryLimit="20mb"/>
>         </policyEntries>
>       </policyMap>
>     </destinationPolicy>
>     <persistenceAdapter>
>       <kahaDB directory="${EmbeddedBroker.dataDirectory}"
>               concurrentStoreAndDispatchQueues="false"/>
>     </persistenceAdapter>
>   </broker>
> Has anybody else seen this ConcurrentModificationException happening with 
> 5.5.0 (or otherwise)?  Any ideas?
> I suppose I should also mention that we're using slf4j 1.6.1.  Not sure if 
> that has anything to do with this, since the stack trace does show it 
> happening in slf4j land...
>     <dependency>
>       <groupId>org.slf4j</groupId>
>       <artifactId>slf4j-api</artifactId>
>       <version>1.6.1</version>
>       <scope>runtime</scope>
>     </dependency>
>     <dependency>
>       <groupId>org.slf4j</groupId>
>       <artifactId>slf4j-jdk14</artifactId>
>       <version>1.6.1</version>
>       <scope>runtime</scope>
>     </dependency> 

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