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Posted to issues@camel.apache.org by "Peter Keller (JIRA)" <ji...@apache.org> on 2016/12/03 08:28:58 UTC
[jira] [Commented] (CAMEL-10272) Unexpected behaviour in aggregator
if recipient list is processed in parallel
[ https://issues.apache.org/jira/browse/CAMEL-10272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15717708#comment-15717708 ]
Peter Keller commented on CAMEL-10272:
--------------------------------------
Alex thank you for the patch.
I updated the title and the description of the issue so that it better suits to the actual problem. I hope that everybody is fine with this.
The analysis of our problem showed that a {{java.util.ConcurrentModificationException}} was thrown in the aggregator. A non thread safe collection was accessed concurrently in every route of the recipient list as well as in the aggregator. This explains properly the unpredictable behaviour.
Thinking about the solution I think the correct way is to pass the exception to the error handler of the main route, even if this brakes the old behaviour. Perhaps this could be controlled by a new option?
> Unexpected behaviour in aggregator if recipient list is processed in parallel
> -----------------------------------------------------------------------------
>
> Key: CAMEL-10272
> URL: https://issues.apache.org/jira/browse/CAMEL-10272
> Project: Camel
> Issue Type: Bug
> Components: camel-core
> Affects Versions: 2.16.3, 2.17.3
> Environment: MacOS 10.11.6, JRE 1.7.0_79
> Reporter: Peter Keller
>
> h3. Problem
> The {{oldExchange}} is {{null}} more than once in the aggregator if a recipient list is processed in parallel.
> h3. Camel route
> In my Camel route, a recipient list is worked of in parallel:
> {code}
> from("direct:start")
> .to("direct:pre")
> .recipientList().method(new MyRecipientListBuilder())
> .stopOnException()
> .aggregationStrategy(new MyAggregationStrategy())
> .parallelProcessing()
> .end()
> .bean(new MyPostProcessor());
> {code}
> Snippet of {{MyAggregationStrategy}}:
> {code}
> @Override
> @SuppressWarnings("unchecked")
> public Exchange aggregate(final Exchange oldExchange, final Exchange newExchange) {
> if (oldExchange == null) {
> // this is the case more than once which is not expected!
> }
> // ...
> {code}
> {{oldExchange}} is null more than once which is not expected and which contradicts the contract with Camel.
> h3. Analysis
> Unfortunately, I am not able to provide a (simple) unit test for comprehending the problem. Furthermore our (complex) unit tests are not deterministic due to the root cause of the problem.
> During the processing, Camel invokes {{ParallelAggregateTask.doAggregateInternal()}}. If aggregation is not done in parallel (as it is the case in our route), this is supposed to be done synchronously:
> {code}
> protected void doAggregateInternal(AggregationStrategy strategy, AtomicExchange result, Exchange exchange) {
> if (strategy != null) {
> // prepare the exchanges for aggregation
> Exchange oldExchange = result.get();
> ExchangeHelper.prepareAggregation(oldExchange, exchange);
> result.set(strategy.aggregate(oldExchange, exchange));
> }
> }
> {code}
> However, is it possible that we face a race condition in {{doAggregateInternal}} even if this method is supposed to be invoked synchronously?
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