heap dump shows StoppableSourceStreamTask retained by java.lang.finalizer

Posted by Steven Wu on
URL: http://deprecated-apache-flink-user-mailing-list-archive.369.s1.nabble.com/heap-dump-shows-StoppableSourceStreamTask-retained-by-java-lang-finalizer-tp15535.html

Hi ,

I was using Chaos Monkey to test Flink's behavior against frequent killing of task manager nodes. I found that stopped/disposed StreamTask got retained by java finalizer. It is kind like a memory leak. Since each StreamTask retains 2.6 MB memory. With 20 kills (and job restarts) for 8-CPU container, there are 2.6 * 20 * 8 MB retained in heap.

finalize() is generally not recommended for cleanup, because "Finalizers are unpredictable, often dangerous, and generally unnecessary", quoted from Joshua Bloch's book.

http://www.informit.com/articles/article.aspx?p=1216151&seqNum=7

This code from StreamTask.java seems to be the cause. Is it necessary? can it be removed? We are using flink-1.2 release branch. But I see the same code in flink-1.3 and master branch

/**

* The finalize method shuts down the timer. This is a fail-safe shutdown, in case the original

* shutdown method was never called.

*

* <p>

* This should not be relied upon! It will cause shutdown to happen much later than if manual

* shutdown is attempted, and cause threads to linger for longer than needed.

*/

@Override

protected void finalize() throws Throwable {

super.finalize();

if (timerService != null) {

if (!timerService.isTerminated()) {

LOG.info("Timer service is shutting down.");

timerService.shutdownService();

}

}

cancelables.close();

}

Thanks,

Steven