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https://issues.apache.org/activemq/browse/CAMEL-1650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=51943#action_51943
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Claus Ibsen commented on CAMEL-1650:
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Thanks for the unit test.
The problem is a bit chicken and egg. Should you add the id before you start
process the message or afterwards?
If you do it before then you have the issue what if the processing failed?
Should the id be removed or should it stay?
Maybe we should expose options so end user can configure
- before
- after
- and if id should be removed in case of failure
> Race condition in IdempotentConsumer
> ------------------------------------
>
> Key: CAMEL-1650
> URL: https://issues.apache.org/activemq/browse/CAMEL-1650
> Project: Apache Camel
> Issue Type: Bug
> Components: camel-core
> Affects Versions: 2.0-M1
> Reporter: Oliver Hecker
> Attachments: IdempotentConsumerTest.java
>
>
> A possible possible race condition exists in the IdempotentConsumer
> implementation:
> The code first checks in the MessageIdRepository if the message was already
> processed. If not then it processes the message and
> afterwards adds the id to the repository. (See also
> http://issues.apache.org/activemq/browse/CAMEL-1451). There is no locking
> between the check with "contains" and the insert with "add". So if multiple
> threads/instances try this in parallel for the same id, then
> it might happen that more than one finds the id not yet contained in the
> repository and the same message is processed multiple
> times.
> I enclose an extended version of IdempotentConsumerTest which illustrates the
> problem.
> It is important to note that even if the test demonstrates the issue with an
> MemoryIdempotentRepository a solution should also
> address the case of a database based respository in a clustered environment.
> So this might imply that some locking mechanism on the
> database is required.
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