RFR(M,v7): JDK-8059036 : Implement Diagnostic Commands for heap and finalizerinfo (original) (raw)

Dmitry Samersoff dmitry.samersoff at oracle.com
Tue May 26 14:14:24 UTC 2015

On 2015-05-21 02:07, Mandy Chung wrote:

On May 19, 2015, at 11:51 PM, Dmitry Samersoff <dmitry.samersoff at oracle.com <mailto:dmitry.samersoff at oracle.com>> wrote:

Other alternatives could be to do all hashing/sorting/printing on native layer i.e. implement printFinalizationQueue inside VM. Both options has pros and cons - Java based solution requires less JNI calls and better readable but takes more memory. It might be better to return an array of Map.Entry<String, int[]> objects to VM rather than one huge string. The output and formatting should be done by jcmd.

done.

What you really need to get a peek on the finalizer queue and print the histogram. The VM has the heap histogram implementation. Have you considered leveraging that?

5: 1012 40480 java.lang.ref.Finalizer

One of previous versions count total a number of instances registered for finalization but then we decided that number of unreachable instances awaiting finalization has more value for customer.

You can find the registered Finalizer instances. The downside is that icmd -finalizerinfo stops the world. I think it’s not unreasonable for this diagnostic command to be expensive like -heap command.

Current implementation is lock-free and don't stop the world, we decided to make it less expensive at the cost of less accurate results.

-Dmitry

-- Dmitry Samersoff Oracle Java development team, Saint Petersburg, Russia

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