RFR: 8252842: Extend jmap to support parallel heap dump [v19]

[Lin Zang]

On Mon, 29 Mar 2021 11:27:49 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> 8252842: Extend jmap to support parallel heap dump
>
> Lin Zang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 24 commits:
> 
>  - Merge branch 'master' into par-dump
>  - Typo fix
>  - remove parallel option and dumpheapext command
>  - Revert "hide the dumpheapext error message"
>    
>    This reverts commit 1af0e1e2bfab4f5d079c03ff0cb25067acacdac4.
>  - resize large object threshold
>  - Merge branch 'master' into par-dump
>  - Merge branch 'master' into par-dump
>  - code clean
>  - fix trailing white space issue
>  - reduce memory consumption and fix memory leak issue
>  - ... and 14 more: https://git.openjdk.java.net/jdk/compare/aefc1560...301cf8cd

Hi Chris, 
I am going to close the CSR https://bugs.openjdk.java.net/browse/JDK-8260424. 
But it seems this PR also revised the `parallel` option's help message for `jmap -histo`, Do you think it is ok to keep the change in the PR? 

FYI, here is the commits https://github.com/openjdk/jdk/pull/2261/commits/6789ba291a97a01fdc70258fb25dbf0d6464dba8

Thanks,
Lin

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PR: https://git.openjdk.java.net/jdk/pull/2261