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https://issues.apache.org/jira/browse/KAFKA-5818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16149975#comment-16149975
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Guozhang Wang commented on KAFKA-5818:
--------------------------------------
Yes, because state is volatile, we only need to synchronize the block that
read-write the variable; for single read operation we do not need to
synchronize it.
> KafkaStreams state transitions not correct
> ------------------------------------------
>
> Key: KAFKA-5818
> URL: https://issues.apache.org/jira/browse/KAFKA-5818
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 0.11.0.1, 1.0.0
> Reporter: Matthias J. Sax
> Assignee: Matthias J. Sax
> Fix For: 0.11.0.1, 1.0.0
>
>
> There is a race condition revealed by failing test
> {{KafkaStreamsTest#testCannotStartTwise}}. It fails with:
> {noformat}
> java.lang.Exception: Unexpected exception,
> expected<java.lang.IllegalStateException> but
> was<java.lang.IllegalThreadStateException>
> Caused by: java.lang.IllegalThreadStateException
> at java.lang.Thread.start(Thread.java:705)
> at org.apache.kafka.streams.KafkaStreams.start(KafkaStreams.java:590)
> at
> org.apache.kafka.streams.KafkaStreamsTest.testCannotStartTwice(KafkaStreamsTest.java:251)
> {noformat}
> The race condition is a follows:
> 1) test calls {{KafkaStreams#start()}} for the first time and state transits
> from CREATED -> RUNNING
> 2) First poll triggers a rebalance and {{StreamThread}} put {{KafkaStreams}}
> into state REBALANCING
> 3) before REBALANCING completes, the main test thread calls
> {{KafkaStream#start()}} again. As current state is REBALANCING, the
> transition to RUNNING is valid and {{start()}} does not fail with
> {{IllegalStateException}} but resumes. When it tries to start internal
> streams, we get {{IllegalThreadStateException}} as thread are already running.
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