RFR: 8270014: Add scoped objects for g1 young gc verification and young gc internal timing [v2]

[Thomas Schatzl]

On Tue, 13 Jul 2021 18:21:16 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix test because of slightly different log message order
>
> src/hotspot/share/gc/g1/g1Policy.hpp line 305:
> 
>> 303: 
>> 304:   void note_young_gc_pause_start();
>> 305:   void note_young_gc_pause_end();
> 
> It's not obvious to me if there's a diff btw `young_gc_pause` and  `young_collection`, or what the diff is. I think having some comments for these two pairs of methods would make it easier to understand.

Added comments. `gc_pause` is the whole pause, `collection` is about just the collection part (as defined by the inner scope of the `do_collection_pause_at_safepoint_helper`). Feel free to suggest better naming.

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PR: https://git.openjdk.java.net/jdk/pull/4768