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

[Aleksey Shipilev]

On Mon, 21 Sep 2020 02:36:18 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> - enable parallel heap inspecton for ShenandoahHeap
>>   - preliminary evaluation:
>>     Time of jmap histo on (8GB heap with 4GB objects)
>>     * before: 5.186s
>>     * after : 1.698s
>
> 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.

Thanks, this looks very good. I have only a few minor stylistic leftovers. Other than that, it seems ready to integrate.

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 1496:

> 1494: };
> 1495:
> 1496: ParallelObjectIterator* ShenandoahHeap::parallel_object_iterator(uint num_workers) {

`num_workers` -> `workers`

src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp line 560:

> 558:   void object_iterate(ObjectClosure* cl);
> 559:   // Parallel heap iteration support
> 560:   virtual ParallelObjectIterator* parallel_object_iterator(uint thread_num);

`thread_num` -> `workers`

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?

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Marked as reviewed by shade (Reviewer).

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