RFR: 8259808: Add JFR event to detect GC locker stall [v2]

[Denghui Dong]

On Mon, 18 Jan 2021 08:10:10 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Refactor based on comments
>
> Not a review, but a few comments about what probably needs to be cleaned up before a proper review starts.

Refactored.

Testing: jdk/jfr all passed.

> src/hotspot/share/gc/shared/gcLocker.cpp line 186:
> 
>> 184:       _stall_count = 0;
>> 185:     }
>> 186: #endif
> 
> This adds a fair amount of noise and hides the actual GCLocker logic, IMHO. Could you somehow encapsulate this code and the other INCLUDE_JFR above into a class and make single-line calls perform these functions?

good idea.
updated.

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PR: https://git.openjdk.java.net/jdk/pull/2088