RFR: 8306738: Select num workers for safepoint ParallelCleanupTask [v2]

[Axel Boldt-Christmas]

On Thu, 27 Apr 2023 19:36:55 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Use active_workers
>
> I think I put the safepoint cleanup ordering code in assuming that the symbol table and string table rehashing takes a long time when it needs rehashing.  But most/all of the time, it only notifies the ServiceThread that these tables need resizing.  You can put those two at the end.  From what I can tell from this, you only need 3 threads maximum to do the cleanup tasks.  Aleksey's expected_workers() function makes a lot of sense to me.

@coleenp @tschatzl 
I'll leave this open until tomorrow for if you have any comments on 1ca4aab23863629d544a8ebe8e87fadda90a0031 and then integrate.

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PR Comment: https://git.openjdk.org/jdk/pull/13616#issuecomment-1538312484