RFR: 8252842: Extend jmap to support parallel heap dump [v32]

[Lin Zang]

On Wed, 8 Sep 2021 05:02:18 GMT, Ralf Schmelter <rschmelter at openjdk.org> wrote:

>> Lin Zang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix build error
>
> I will start reviewing this today.

Hi Ralf @schmelter-sap, 
     I have updated the PR, would you like to help review it again? Thanks!

BRs,
Lin

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