RFR: 8248149: G1: change _cleaning_claimed from int to bool

[Kim Barrett]

On Thu, 15 Jun 2023 11:01:18 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> src/hotspot/share/gc/g1/g1ParallelCleaning.cpp line 43:
>> 
>>> 41:   }
>>> 42: 
>>> 43:   return !Atomic::cmpxchg(&_cleaning_claimed, false, true);
>> 
>> It might be an int because making it a bool may involve a byte-sized cmpxchg, which has a not very
>> nice implementation on some platforms.  Though even with that the claim cost is likely dwarfed by
>> other costs here.
>
> I prefer to believe that when this has been implemented, there has been no cmpxchg overload for bools before the atomics refactoring. We did not go back and look for these kind of mismatches.
> 
> There should be no visible performance difference, so I prefer using the more appropriate type.

Yeah, that's probably correct.  We used to have a cmpxchg overload for jbyte, but never explicitly bool.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14487#discussion_r1231399226