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https://issues.apache.org/jira/browse/AMQ-5263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16611946#comment-16611946
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Krzysztof Mackowiak commented on AMQ-5263:
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In my team we experienced the same issue with ActiveMQSession.close() and
ActiveMQSession.commit() methods running concurrently. In our case the bug
manifested not by NullPointerException, but by losing messages during failover
between 2 instances of ActiveMQ broker.
According to ActiveMQSession documentation calling close() method in another
thread than a thread which is handling messages should be thread-safe. This
method is called during failover from one instance of ActiveMQ broker to
another when the master is stopped.Unfortunately, it looks that close() method
is NOT safe to call from another thread. When it is called from another thread
we may end up with a situation when ActiveMQSession.commit() method ends
without any exception but underneath ‘rollback message’ (TransactionInfo with
type ROLLBACK) is sent to a broker. So a message is lost.
I've attached a test which simulates this situation.
> Method ActiveMQSession.close() is not thread safe as declared and required
> --------------------------------------------------------------------------
>
> Key: AMQ-5263
> URL: https://issues.apache.org/jira/browse/AMQ-5263
> Project: ActiveMQ
> Issue Type: Bug
> Components: JMS client
> Affects Versions: 5.9.1
> Environment: any operationg system, and any platform
> Reporter: Jiang Fuqiang
> Priority: Major
>
> If ActiveMQSession.close() and ActiveMQSession.dispose() run concurrently,
> the statements in close() method might throw NullPointerException。Just marked
> by the following code snippet.
> -------------------------------
> public void ActiveMQSession.close() throws JMSException {
> if (!closed) {
> if (getTransactionContext().isInXATransaction()) { // it might
> throw NullPointerException
> ...
> -------------------------------
> In my application, I call Session.close() when I detect JMSException, but
> Session.close() throws NullPointerException occasionally。I suspect that's
> because ActiveMQConnection called ActiveMQSession.dispose() in case of
> transport error, and ActiveMQSession.dispose() nullified
> ActiveMQSession.transactionContext before ActiveMQSession.closed is assigned
> to false. Since this NullPointerException error just happened once and can
> not be reproduced, it's only a suspection.
> It seems that close() and dispose() should be synchronized, and then sessions
> can be closed safely.
> I'm not good at English, but I hope this issue is demonstrated clearly enough.
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