RFR: 8252104: parallel heap inspection for ShenandoahHeap [v4]

[Lin Zang]

On Mon, 21 Sep 2020 05:52:32 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Lin Zang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views
>> will show differences compared to the previous content of the PR. The pull request contains one new commit since the
>> last revision:
>>   8252104: parallel heap inspection for ShenandoahHeap
>>   
>>     - enable parallel heap inspecton for ShenandoahHeap
>>     - preliminary evaluation:
>>       Time of jmap histo on (8GB heap with 4GB objects)
>>       * before: 5.186s
>>       * after : 1.698s
>
> Thanks, this looks very good. I have only a few minor stylistic leftovers. Other than that, it seems ready to integrate.

Dear @shipilev,
   I just updated the patch.  may I ask your help to review and merge it if there is no problem? Thanks!
-Lin

> src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp line 531:
> 
>> 529:   void finish_concurrent_unloading();
>> 530:   // Heap iteration support
>> 531:   void scan_roots_for_iteration(Stack<oop, mtGC>* oop_stack, ObjectIterateScanRootClosure* oops);
> 
> Let's `typedef Stack<oop, mtGC> ShenandoahScanRootStack` and use it everywhere?

As this Stack is also used for iterating all objects (not only roots), so I took the liberty to rename it to
ShenandoahScanObjectStack :)

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PR: https://git.openjdk.java.net/jdk/pull/67