RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v17]

[Doug Lea]

On Fri, 31 May 2024 14:04:50 GMT, Viktor Klang <vklang at openjdk.org> wrote:

>> Doug Lea has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Reconcile changes
>
> src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 2024:
> 
>> 2022:                                 }
>> 2023:                                 if (pb == (pb = b))       // base unchanged
>> 2024:                                     Thread.onSpinWait();
> 
> @DougLea Doesn't this mean that we'll always onSpinWait at least once here (since pb is initialized to -1 and not written until this check)

No, almost the opposite: it only spinWaits if base is apparently stuck, except (harmlessly) every 4B encounters when it happens to be -1. (The value -1 works best here since base starts at 0 and is simpler than other ways of checking for stalls.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1622505491