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https://issues.apache.org/jira/browse/AMQ-5198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14041896#comment-14041896
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Enrico Musuruana commented on AMQ-5198:
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Hi Timothy,
As I mentioned the problem is not related to the Session, but the Connection
itself not being thread safe. We currently make use of a single Session per
thread.
We both agree that an 'in frequently triggered' race condition doesnt exactly
lend itself to a simple junit, but I believe that the test case I provided you
with the actual patch should be quite straight-forward to test.
> MessageConsumer and Producer are not thread safe
> ------------------------------------------------
>
> Key: AMQ-5198
> URL: https://issues.apache.org/jira/browse/AMQ-5198
> Project: ActiveMQ
> Issue Type: Bug
> Affects Versions: 5.9.0
> Reporter: Enrico Musuruana
> Attachments: ActiveMq.zip
>
>
> We currently have an object that acts both as a consumer and as a producer
> over the same queue.
> Lazy initialization of the scheduler is not 100% thread safe when a consumer
> and a producer are created sharing the same connection.
> We encountered the following sporadic NPE when a rollback() is invoked:
> Caused by: java.lang.NullPointerException
> at
> org.apache.activemq.thread.Scheduler.executeAfterDelay(Scheduler.java:64)
> at
> org.apache.activemq.ActiveMQMessageConsumer.rollback(ActiveMQMessageConsumer.java:1278)
> at
> org.apache.activemq.ActiveMQMessageConsumer$5.afterRollback(ActiveMQMessageConsumer.java:1054)
> at
> org.apache.activemq.TransactionContext.afterRollback(TransactionContext.java:157)
> ... 11 more
> We believe that the lazy initialized getScheduler() is open for a race
> condition when a publish and rollback are happening concurrently.
> try {
> result = scheduler = new
> Scheduler("ActiveMQConnection["+info.getConnectionId().getValue()+"]
> Scheduler");
> scheduler.start();
> } catch(Exception e) {
> throw JMSExceptionSupport.create(e);
> }
> The suggested fix is to simply invoke the start within the constructor of the
> Scheduler class.
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