RFR: 8225631: Consider replacing muxAcquire/Release with PlatformMonitor [v4]

[Daniel D.Daugherty]

On Tue, 17 Nov 2020 22:35:20 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> This RFE was filed a while ago to see if we could get rid of `muxAcquire/release` to reduce overall code complexity. Initially some usages seemed to suffer some slight performance loss when I tried this. However, since then all but one usage have been removed and the final case, the `gInflationLock`'s in `ObjectSynchronizer read_stable_mark` does not suffer any performance degradation. It can also use `PlatformMutex` rather than `PlatformMonitor`.
>> 
>> On the plus side we remove a large chunk of complex synchronization code, we delete a `ParkEvent` per thread, and an int field per `ParkEvent` - which is good for footprint.
>> 
>> Testing:
>> - GH actions
>> - mach5 tiers 1-3
>> - selected performance testing (guided by that used for JDK-8253064)
>> 
>> Thanks,
>> David
>
> David Holmes 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 six additional commits since the last revision:
> 
>  - Update power_of_2 static assertion placement.
>  - Merge branch 'master' into 8225631
>  - Move static_assert as requested by Kim.
>  - Merge branch 'master' into 8225631
>  - Feedback from Coleen, Kim and Dan.
>  - 8225631: Consider replacing muxAcquire/Release with PlatformMonitor

Still good.

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Marked as reviewed by dcubed (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1196