RFR: JDK-8261034: improve jcmd GC.class_histogram to support parallel

Sat Feb 13 05:08:40 UTC 2021

On Sat, 13 Feb 2021 04:39:04 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> > There is a limitation of parallel thread number so that it never exceed the total_workers defined in hotspot.
> > so how about we just print how many threads worked on parallel heap insecption and then user get the clue to tune it?
> 
> How to we print the number of threads? It's not know to jmap.

Yes, It is not known at present, but the heapInspect and heapDumper accept an outputStream, and the actual parallel thread number can be got by gang->active_workers() after WithUpdatedActiveWorkers.  Then maybe some code can be added there to record the actual number and finally print to outputStream at the end.

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PR: https://git.openjdk.java.net/jdk/pull/2379