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https://issues.apache.org/jira/browse/CAMEL-10272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15717708#comment-15717708
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Peter Keller commented on CAMEL-10272:
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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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