RFR: 8225631: Consider replacing muxAcquire/Release with PlatformMonitor

[Daniel D.Daugherty]

On Fri, 13 Nov 2020 00:51:02 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

I'm good with this fix modulo resolving @coleenp's comments
about making NINFLATIONLOCKS and gInflationLocks exported.

src/hotspot/share/runtime/thread.cpp line 4607:

> 4605: // mechanism.
> 4606: //
> 4607: // Testing has shown that contention on the ListLock guarding gFreeList

Ouch! I missed a reference to `gFreeList`. Sorry about that.

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Marked as reviewed by dcubed (Reviewer).

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