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Date: Fri, 2 Dec 2016 17:08:58 +0000 (UTC)
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Subject: [jira] [Commented] (CAMEL-10272) Aggregation is broken due to race
 condition in ParallelAggregateTask.doAggregateInternal()
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archived-at: Fri, 02 Dec 2016 17:09:00 -0000


    [ https://issues.apache.org/jira/browse/CAMEL-10272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15715672#comment-15715672 ] 

ASF GitHub Bot commented on CAMEL-10272:
----------------------------------------

Github user asfgit closed the pull request at:

    https://github.com/apache/camel/pull/1326


> Aggregation is broken due to race condition in ParallelAggregateTask.doAggregateInternal()
> ------------------------------------------------------------------------------------------
>
>                 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
>
> 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.
> However I tried to analyze the Camel Java code, to work out the problem. Please find below my findings.
> 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
> During the processing, Camel invokes {{MulticastProcessor.process()}}. Here the result object {{AtomicExchange}} is created which is shared during the whole processing.
> If the processing should be done in parallel (as it is the case for our route) then {{MulticastProcessor.doProcessParallel()}} is invoked. Here one instance of {{AggregateOnTheFlyTask}} is initialized and {{aggregateOnTheFly()}} is invoked -*asynchronously* via {{run()}}  for *every* target in the recipient list-. via {{aggregateExecutorService.submit}} ({{aggregationTaskSubmitted}} guarantees that this is only be done once)
> In {{aggregateOnTheFly()}}, a new instance of {{ParallelAggregateTask}} is generated, and if aggregation is not done in parallel (as it is the case in our route), {{ParallelAggregateTask.run()}}, {{ParallelAggregateTask.doAggregate()}} (this method is synchronized), and 
> {{ParallelAggregateTask.doAggregateInternal()}} is invoked 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, in {{ParallelAggregateTask.doAggregateInternal()}} there may occur a race condition as {{result}} is shared -by every instance of {{AggregateOnTheFlyTask}}- such that {{oldExchange = result.get()}} may be {{null}} more than once!
> Note: As a new instance of {{ParallelAggregateTask}} for every target in recipient list is created, the {{synchronized}} method {{ParallelAggregateTask.doAggregate()}} does not prevent the race condition!
> Does this sounds reasonably?


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