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https://issues.apache.org/jira/browse/CAMEL-11750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16156805#comment-16156805
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Önder Sezgin commented on CAMEL-11750:
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hmm, i see what you mean but i still think that putting 1 second delay to each
item in the queue incrementally did not seem right to me.
there must be better solution. because such change may break short running
tasks as my initial look to your PR. [~davsclaus] can better comment on this.
> Camel route with multicast (parallel) generate huge CPU load
> ------------------------------------------------------------
>
> Key: CAMEL-11750
> URL: https://issues.apache.org/jira/browse/CAMEL-11750
> Project: Camel
> Issue Type: Bug
> Components: camel-core
> Reporter: Nazar Vishka
> Priority: Critical
>
> I've created simple [Spring Camel Route
> application|https://github.com/leofromgroza/camel-long-term-route] that can
> be used for issue reproducing. Here we have very simple route:
> {code}
> public void configure() throws Exception {
> from("direct:start").routeId("start")
> .multicast().parallelProcessing()
> .to("direct:very-long-task", "direct:long-task")
> .end();
> from("direct:long-task").routeId("long-task")
> .log("Started long-task")
> .process(exchange -> Thread.sleep(5000))
> .log("Finished long-task")
> .end();
> from("direct:very-long-task").routeId("very-long-task")
> .log("Started very-long-task")
> .process(exchange -> Thread.sleep(35000))
> .log("Finished very-long-task")
> .end();
> }{code}
> From our main route 'start' we are starting in parallel two sub-routes:
> 'long-task' and 'very-long-task'. They are just doing something for some
> period of time and do not generate any load to the system.
> But I found that when one task finished earlier than other one, route start
> to make a huge CPU load. Here you can see a CPU usage during executiong of
> Camel route that was mentioned earlier (after finishing of 'long-task' usage
> of CPU uncreased from 0 to 12.5%):
> !https://content.screencast.com/users/NazarV/folders/Jing/media/830268f0-d184-4c57-adb1-b782ea63fa6d/2017-09-06_1241.png!
> Screenshot was made when I was running route on my Windows PC with 4 physical
> CPU cores + 4 HT. On Unix systems we found that after end of 'long-task' it
> used 100% of one core till the end of work.
> One more interesting thing that i've found is that the main load on the
> system was generated by the thread MulticastProcessor-AggregateTask that was
> spending a lot of time in the method
> java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject#awaitNanos
> that was called from java.util.concurrent.DelayQueue#poll(long,
> java.util.concurrent.TimeUnit):
> {code}"Camel (camel-1) thread #2 - MulticastProcessor-AggregateTask" #29
> daemon prio=5 os_prio=0 tid=0x00000000215e3000 nid=0x7a0 runnable
> [0x0000000022eaf000]
> java.lang.Thread.State: RUNNABLE
> at java.lang.Thread.isInterrupted(Native Method)
> at java.lang.Thread.interrupted(Thread.java:944)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.checkInterruptWhileWaiting(AbstractQueuedSynchronizer.java:2002)
> at
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2079)
> at java.util.concurrent.DelayQueue.poll(DelayQueue.java:273)
> at
> org.apache.camel.util.concurrent.SubmitOrderedCompletionService.poll(SubmitOrderedCompletionService.java:127)
> at
> org.apache.camel.processor.MulticastProcessor$AggregateOnTheFlyTask.aggregateOnTheFly(MulticastProcessor.java:463)
> at
> org.apache.camel.processor.MulticastProcessor$AggregateOnTheFlyTask.run(MulticastProcessor.java:418)
> at
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> at java.util.concurrent.FutureTask.run(FutureTask.java:266)
> at
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
> at
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> at java.lang.Thread.run(Thread.java:745){code}
> In DelayQueue#poll(long, java.util.concurrent.TimeUnit) we have a piece of
> code:
> {code}E first = q.peek();
> if (first == null) {
> ...
> } else {
> long delay = first.getDelay(NANOSECONDS);
> ...
> long timeLeft = available.awaitNanos(delay) {code}
> During debugging I found that E first is object of class
> [org.apache.camel.util.concurrent.SubmitOrderedCompletionService.SubmitOrderFutureTask|https://github.com/apache/camel/blob/camel-2.19.2/camel-core/src/main/java/org/apache/camel/util/concurrent/SubmitOrderedCompletionService.java]
> and it's very interesting [getDelay(TimeUnit)
> method|https://github.com/apache/camel/blob/camel-2.19.2/camel-core/src/main/java/org/apache/camel/util/concurrent/SubmitOrderedCompletionService.java#L64]
> always return 1. I thing that is a source of current issue:
> {code} public long getDelay(TimeUnit unit) {
> // if the answer is 0 then this task is ready to be taken
> return id - index.get();
> }{code}
> So when delay is 1, AggregateTask thread is not sleeping at all and generates
> a huge CPU load all the time when it is waiting for the end of the last task.
> I think that [getDelay(TimeUnit)
> method|https://github.com/apache/camel/blob/camel-2.19.2/camel-core/src/main/java/org/apache/camel/util/concurrent/SubmitOrderedCompletionService.java#L64]
> should be somehow re-implemented.
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