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

[Daniel D. Daugherty]

On Tue, 18 Apr 2023 21:09:54 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.

These changes were tested with a new test that's in the bug report and
with Mach5 Tier[1-8] testing.

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PR Comment: https://git.openjdk.org/jdk/pull/13519#issuecomment-1513803532