Details
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Bug
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Status: Closed
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Major
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Resolution: Duplicate
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5.10.0
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None
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None
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Patch Available
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Regression
Description
This issue is seen on the surface with the broker failing to remove a consumer:
2014-12-19 10:45:42,586 | WARN | Failed to remove consumer:
ID:hack-34927-1419007505006-2:3:0:0 |
org.apache.activemq.broker.TransportConnection | ActiveMQ
BrokerService[broker0] Task-6
java.lang.IllegalStateException: Timer already cancelled.
The full stack trace [STACK_TRACE] will be specified at the end of this report.
In this case, the race condition is exposed via some of the AdvisoryBroker code while trying to send an advisory message as part of the consumer/producer addition/removal code. Below are excerpts of code to explain this race condition:
activemq-broker/src/main/java/org/apache/activemq/advisory/AdvisoryBroker.java
Lines 605 - 637 [in fireAdvisory(...)]
if (getBrokerService().isStarted()) {
// code to create and populate an advisory message
next.send(producerExchange, advisoryMessage);
// send will trigger destination creation/addition for this advisory message topic
}
However, it can easily happen that a client (consumer or producer) connects and is added before getBrokerService().isStarted() is true, so in that case, the boolean expression in the block above will evaluate to false and hence skip the entire advisory message send and create/add destination process. At this point, the consumer/producer destination does not have its advisory message destination created. If no other consumer/producer connects on the same destination until the broker is shutting down, then no advisory destination pairing will be created for that consumer/producer. When the broker starts the shutdown process, the event that will trigger an advisory message will be the removal of a consumer/producer as part of the TransportConnection stopping process. The sequence of calls with line numbers can be seen within the STACK_TRACE.
Back to the above specified code block, when the broker is shutting down, the broker is still in the started state. Then, the boolean expression will evaluate to true and hence proceed with the advisory message creation/sending and destination creation/addition process. However, in the meantime, as part of the shutdown process, the Scheduler timer is being cancelled. Consider the following blocks of code:
activemq-broker/src/main/java/org/apache/activemq/broker/BrokerService.java
Lines 756 - 761 [in stop()]
// for each service
stopper.stop(service);
activemq-client/src/main/java/org/apache/activemq/util/ServiceSupport.java
Lines 67 - 84 [in stop()]
if (stopped.compareAndSet(false, true)) {
... some code ...
doStop(stopper);
... some code ...
}
activemq-client/src/main/java/org/apache/activemq/thread/Scheduler.java
Lines 69 - 71 [in doStop(...)]
if (this.timer != null) {
this.timer.cancel();
}
At this point, the timer is cancelled. Now, back to the thread removing the consumer. From the STACK_TRACE, it can be seen that after many calls related to the advisory message destination creation, it ends up in AbstractRegion’s addDestination method.
activemq-broker/src/main/java/org/apache/activemq/broker/region/AbstractRegion.java
Lines 132 - 145 [in addDestination(...)]
if (dest == null) {
... some code ...
dest = createDestination(context, destination);
... some code ...
dest.start();
... some code ...
}
As it can be seen in the STACK_TRACE below, dest.start() call will trigger the need for a timer to be scheduled on the same timer that has already been cancelled. Some debug prints to confirm the race condition:
1. Fail to send advisory message for this consumer advisory topic because getBrokerService().isStarted() is false:
2015-01-06 08:49:26,215 | INFO | patanasov: from AdvisoryBroker fireAdvisory would have sent advisoryMessage: topic ActiveMQ.Advisory.Consumer.Queue.2015.01.06-08.23.00.16401 | org.apache.activemq.advisory.AdvisoryBroker
2. Broker shutting down and cancelling timer:
2015-01-06 08:49:43,602 | INFO | Apache ActiveMQ 5.10.0 (broker0, ID:host-40197-1420555763149-0:1) is shutting down | org.apache.activemq.broker.BrokerService | ActiveMQ ShutdownHook
2015-01-06 08:49:43,603 | INFO | patanasov: from ServiceSupport calling doStop(stopper) | org.apache.activemq.util.ServiceSupport | ActiveMQ ShutdownHook
2015-01-06 08:49:43,603 | INFO | patanasov: from Scheduler doStop(ServiceStopper stopper) calling this.timer.cancel(): timer java.util.Timer@7df33bb0 | org.apache.activemq.thread.Scheduler | ActiveMQ ShutdownHook
3. Adding destination and scheduling on cancelled timer (7df33bb0):
2015-01-06 08:49:43,767 | INFO | patanasov: broker0 adding destination: qualified: topic://ActiveMQ.Advisory.Consumer.Queue.2015.01.06-08.23.00.16401, physical: ActiveMQ.Advisory.Consumer.Queue.2015.01.06-08.23.00.16401 | org.apache.activemq.broker.region.AbstractRegion | ActiveMQ BrokerService[broker0] Task-12
2015-01-06 08:49:43,782 | INFO | patanasov: from schedualPeriodically: timer: java.util.Timer@7df33bb0 | org.apache.activemq.thread.Scheduler | ActiveMQ BrokerService[broker0] Task-12
2015-01-06 08:49:43,785 | INFO | patanasov: caught an exception in schedualPeriodically: | org.apache.activemq.thread.Scheduler | ActiveMQ BrokerService[broker0] Task-12
java.lang.IllegalStateException: Timer already cancelled.
I will provide a patch to fix this issue. However, the bigger concern here is that advisory message destination creations fail for clients that connect while getBrokerService().isStarted() is false. If there is only one consumer/producer on one destination and if it connects while getBrokerService().isStarted() is false, then it will fail to create/send advisory message for that destination, at least until the producer/consumer is removed at the end. I will continue looking to learn more about this state of the broker and open a separate JIRA issue if needed.
STACK_TRACE:
java.lang.IllegalStateException: Timer already cancelled.
at java.util.Timer.sched(Timer.java:354)
at java.util.Timer.schedule(Timer.java:222)
at
org.apache.activemq.thread.Scheduler.schedualPeriodically(Scheduler.java:53)
at org.apache.activemq.broker.region.Topic.start(Topic.java:563)
at
org.apache.activemq.broker.region.AbstractRegion.addDestination(AbstractRegion.java:141)
at
org.apache.activemq.broker.region.RegionBroker.addDestination(RegionBroker.java:325)
at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:167)
at
org.apache.activemq.advisory.AdvisoryBroker.addDestination(AdvisoryBroker.java:184)
at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:167)
at
org.apache.activemq.broker.BrokerFilter.addDestination(BrokerFilter.java:167)
at
org.apache.activemq.broker.MutableBrokerFilter.addDestination(MutableBrokerFilter.java:172)
at
org.apache.activemq.broker.region.RegionBroker.send(RegionBroker.java:439)
at
org.apache.activemq.broker.jmx.ManagedRegionBroker.send(ManagedRegionBroker.java:297)
at
org.apache.activemq.advisory.AdvisoryBroker.fireAdvisory(AdvisoryBroker.java:615)
at
org.apache.activemq.advisory.AdvisoryBroker.fireConsumerAdvisory(AdvisoryBroker.java:564)
at
org.apache.activemq.advisory.AdvisoryBroker.fireConsumerAdvisory(AdvisoryBroker.java:550)
at
org.apache.activemq.advisory.AdvisoryBroker.removeConsumer(AdvisoryBroker.java:271)
at
org.apache.activemq.broker.BrokerFilter.removeConsumer(BrokerFilter.java:132)
at
org.apache.activemq.broker.BrokerFilter.removeConsumer(BrokerFilter.java:132)
at
org.apache.activemq.broker.MutableBrokerFilter.removeConsumer(MutableBrokerFilter.java:137)
at
org.apache.activemq.broker.TransportConnection.processRemoveConsumer(TransportConnection.java:651)
at
org.apache.activemq.broker.TransportConnection.processRemoveSession(TransportConnection.java:690)
at
org.apache.activemq.broker.TransportConnection.processRemoveConnection(TransportConnection.java:802)
at
org.apache.activemq.broker.TransportConnection.doStop(TransportConnection.java:1143)
at
org.apache.activemq.broker.TransportConnection$4.run(TransportConnection.java:1073)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
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