RFR: 8252842: Extend jmap to support parallel heap dump

[Lin Zang]

On Thu, 28 Jan 2021 07:36:44 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> Hi Lin,
>> It is also in my memory that you actually did not have 4 arguments.
>> The real incompatibility issue was that the order of arguments was swapped.
>> It is why it was relatively easy to fall back and just update the constants with 3 instead of 4 and swap the order of arguments back.
>> Thanks,
>> Serguei
>
> Dear Serguei, 
> Yes,  you are right! 
> However, for this PR it seems I have to deal with four arguments for jmap -d : file, live, gz=, parallal=. 
> 
> BRs,
> Lin

Dear All, 
I have another idea. How about I don't introduce parallel parameter to jmap , but instead just enable parallel heap dump by default as long as there is more than one active workers? 
In this way there is no need to have an parallel option for jmap, and this PR don't even bother with a CSR.
The down side is that user can not control how much threads they want to use for parallel dump. (P.S This may not even guaranteed with "parallel" option because in JDK the actually number of thread used is decided by number of compression backends and active workers).
what's your opinion?

BRs,
Lin

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