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Seweryn Habdank-Wojewodzki commented on KAFKA-4366:
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Questions:
* If I will use close(...) with timeout, could it be the case, that I am losing messages?
* What exactly is happening, when timeout is reached?
* What are the consequences of calling close(...) with timeout?
* I had also problems with hanging close(), which in background is calling close(0), but why
it can hangs?
Thanks in advance for ansers :-).
> KafkaStreams.close() blocks indefinitely
> ----------------------------------------
>
> Key: KAFKA-4366
> URL: https://issues.apache.org/jira/browse/KAFKA-4366
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 0.10.0.1, 0.10.1.0
> Reporter: Michal Borowiecki
> Assignee: Damian Guy
> Fix For: 0.10.2.0
>
> Attachments: threadDump.log
>
>
> KafkaStreams.close() method calls join on all its threads without a timeout, meaning
indefinitely, which makes it prone to deadlocks and unfit to be used in shutdown hooks.
> (KafkaStreams::close is used in numerous examples by confluent: https://github.com/confluentinc/examples/tree/kafka-0.10.0.1-cp-3.0.1/kafka-streams/src/main/java/io/confluent/examples/streams
and https://www.confluent.io/blog/introducing-kafka-streams-stream-processing-made-simple/
so we assumed it to be recommended practice)
> A deadlock happens, for instance, if System.exit() is called from within the uncaughtExceptionHandler.
(We need to call System.exit() from the uncaughtExceptionHandler because KAFKA-4355 issue
shuts down the StreamThread and to recover we want the process to exit, as our infrastructure
will then start it up again.)
> The System.exit call (from the uncaughtExceptionHandler, which runs in the StreamThread)
will execute the shutdown hook in a new thread and wait for that thread to join. If the shutdown
hook calls KafkaStreams.close, it will in turn block waiting for the StreamThread to join,
hence the deadlock.
> Runtime.addShutdownHook javadocs state:
> {quote}
> Shutdown hooks run at a delicate time in the life cycle of a virtual machine and should
therefore be coded defensively. They should, in particular, be written to be thread-safe and
to avoid deadlocks insofar as possible
> {quote}
> and
> {quote}
> Shutdown hooks should also finish their work quickly.
> {quote}
> Therefore the current implementation of KafkaStreams.close() which waits forever for
threads to join is completely unsuitable for use in a shutdown hook.
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