RFR: 8252842: Extend jmap to support parallel heap dump [v10]

[Ralf Schmelter]

On Thu, 18 Mar 2021 11:07:16 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> Dear Ralf @schmelter-sap, 
>> Sorry for late response, I got stuck in other work recently.
>> I have uploaded a new update that could help reduce memory consumption and also fix the assertion issue. 
>> I have verified it on my machine, May I ask your help to double check it on your side? 
>> Thanks!
>> Lin
>
> Dear Chris and Ralf,
> May I ask your help to review the related CSR first? both JDK-8260424  and JDK-8261943? 
> https://bugs.openjdk.java.net/browse/JDK-8260424 is for adding `parallel=<N>` option, which IMO also block the merge of #2379. 
> https://bugs.openjdk.java.net/browse/JDK-8261943 is for adding new attach api comment `dumpheapext`
> 
> Thanks
> Lin

Hi Lin,

to be honest I would prefer if we would not add the parallel option but instead do it automatically depending on the number of GC threads available. I doubt that the user has a good idea about number of threads to use, so I think it is better to just use a sensible default derived from the number of threads available and if compression is enabled or not.

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