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

[Coleen Phillimore]

On Tue, 25 Apr 2023 14:34:06 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> Select num workers for safepoint ParallelCleanupTask to be at most the number of parallel cleanup tasks `SAFEPOINT_CLEANUP_NUM_TASKS`
>> 
>> Unsure if `WorkerThreads::max_workers()` is more correct than `WorkerThreads::created_workers()` or `WorkerThreads::active_workers()`. 
>> 
>> Tested tier1-3 Oracle platforms.
>
> 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.

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PR Comment: https://git.openjdk.org/jdk/pull/13616#issuecomment-1526265467