RFR: 8392760: Improve liveness/remembered set verification for G1 [v2]

[Thomas Schatzl]

On Wed, 22 Feb 2023 06:52:57 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
>> 
>>  - Refactoring after 8302975
>>  - initial attempts, nothing done
>>    
>>    further cleanup
>>    
>>    more cleanup
>>    
>>    factor out changes that move the verifylivenessclosure
>>    
>>    fix compilation
>>    
>>    kbarrett review, indentation
>>    
>>    Minor removal of unnecessary code
>>    
>>    initial version
>>    
>>    more cleanup
>>    
>>    More improvements
>>    
>>    More removal of stuff
>>    
>>    More cleanup
>>    
>>    More^2 cleanup
>>    
>>    Remove some changes
>>    
>>    More cleanups
>>    
>>    fix compilation
>>    
>>    Cleanup
>>  - removal
>
> src/hotspot/share/gc/g1/heapRegion.cpp line 517:
> 
>> 515:       LogStream ls(log.error());
>> 516: 
>> 517:       MutexLocker x(G1RareEvent_lock, Mutex::_no_safepoint_check_flag);
> 
> [pre-existing] It's not clear to me what this lock is protecting.  Similarly for the one in `verify_remset`
> (in an unmodified part of it).

Having this lock avoids the log messages for a single failures (these are multiple lines each) to not mix. Otherwise it would be very hard to analyze the failures. Does that make sense?

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PR: https://git.openjdk.org/jdk/pull/12660