RFR: 8322732: ForkJoinPool may underutilize cores in async mode [v7]

[Viktor Klang]

On Wed, 29 May 2024 11:33:40 GMT, Doug Lea <dl at openjdk.org> wrote:

>> This set of changes address causes of poor utilization with small numbers of cores due to overly aggressive contention avoidance. A number of further adjustments were needed to still avoid most contention effects in deployments with large numbers of cores
>
> Doug Lea 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 41 additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Add test for utilization with interdependent tasks
>  - Un-misplace onSpinWait call
>  - Adjust control flow
>  - Reduce memory stalls
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - More performance tradoffs
>  - Address review comments
>  - Merge branch 'openjdk:master' into JDK-8322732
>  - Repack some fields; adjust control flow
>  - ... and 31 more: https://git.openjdk.org/jdk/compare/01d11057...cf5fe55c

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 1969:

> 1967:                 else if ((e & SHUTDOWN) == 0)
> 1968:                     return 0;
> 1969:                 else if (compareAndSetCtl(c, c) && casRunState(e, e | STOP))

is the `compareAndSetCtl(c, c)` needed for the read+write fence if ctl == c?

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PR Review Comment: https://git.openjdk.org/jdk/pull/19131#discussion_r1618963723