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

[Hamlin Li]

On Wed, 3 Feb 2021 12:44:53 GMT, Hamlin Li <mli at openjdk.org> wrote:

> parallel -histo of jmap was added by JDK-8214535, it's better to support parallel for jcmd GC.class_histogram too.

> Hi @Hamlin-Li,
> 
> It looks good in general.
> A question: What is going to happen if the number of parallel threads passed to the command is too big? Is there any limit, and what has to be the expected behavior in such a case? I'll look at the CSR.
> Thanks,
> Serguei

Hi Serguer,
Thanks for reviewing.
First, it got truncated as uint by ClassHistogramDCmd, then it got capped by by total_workers of gang, so finally it will not exceed total_workers.
Hope this answer your questions.

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