RFR: 8305670: Performance regression in LockSupport.unpark with lots of idle threads [v9]

[David Holmes]

On Wed, 10 May 2023 22:23:03 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Address the performance regression in `LockSupport.unpark()` with the following changes:
>> - Add `FastThreadsListHandle` helper class to threadSMR.[ch]pp for quickly determining if a JavaThread* is protected by the ThreadsListHandle embedded in the new helper object.
>> - Update `Unsafe_Unpark()` to pass `java_lang_Thread::thread_acquire(thread_oop)` to a new instance of the `FastThreadsListHandle` object and only do the unpark work if the target JavaThread* is protected.
>
> Daniel D. Daugherty has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 10 commits:
> 
>  - Merge branch 'JDK-8307068' into JDK-8305670
>  - dholmes CR - FastThreadsListHandle ctr should use java_lang_Thread::thread() instead of java_lang_Thread::thread_acquire(); clarify comments.
>  - Merge branch 'JDK-8307068' into JDK-8305670
>  - Merge JDK-8305670 with code review changes in JDK-8307068.
>  - Merge branch 'JDK-8307068' into JDK-8305670
>  - Merge branch 'jdk-21+20' into JDK-8305670
>  - 8305670.with-rehn-quick-mode.cr3.patch
>  - Use optimized logic in Unsafe_Unpark() instead of cv_internal_thread_to_JavaThread().
>  - dholmes CR - add more comments.
>  - 8305670.with-rehn-quick-mode.cr0.patch

Thanks Dan - looks good.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13519#pullrequestreview-1421722937