KAFKA-18337: KafkaProducer Memory Leak in JmxReporter Class

[tmw090906]

Add a close status in JmxReporter, that avoid re-registering metrics to jmx after being closed, which could lead to memory leaks

relate KAFKA-18337

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

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[AndrewJSchofield]

Thanks for the PR. It seems to me that the new defensive code is right down inside the reregister method, but I would have thought that the check on closed could be in the public methods such as init, metricChange and metricRemoval. All of the MBeans were unregistered when the reporter was closed already. wdyt?

[tmw090906]

Thanks for your reply! It seems that all the public methods will eventually call the reregister and the unregister . I think that the unregister method poses no potential risks after the JmxReporter is closed, so I put the check in the reregister method. wdyt?