RFR: 8225631: Consider replacing muxAcquire/Release with PlatformMonitor

[Kim Barrett]

On Mon, 16 Nov 2020 21:12:55 GMT, Daniel D. Daugherty <dcubed 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 guessing that @dholmes-ora put it in initialize() because
> it only needs to be checked once rather than every time the
> table is used.

> > The initialize() function is the wrong place.  There's nothing in initialize that cares.  The place for the assert is with the code that cares that it's a power of 2.
> 
> As Dan indicated I put it there so that it is only checked once - no
> point checking it on every use. Initialization code is often used to
> check invariants.

A static assert is checked once at compile time.  And my opinion probably wouldn't be different if it were a runtime assert.

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