RFR: 8291714: Implement a Multi-Reader Single-Writer mutex for Hotspot [v5]

[Kim Barrett]

On Mon, 29 Aug 2022 08:47:31 GMT, Johan Sjölén <duke at openjdk.org> wrote:

>> May I please have a review for this PR which implements a `MRWMutex` class for Hotspot?
>> 
>> This PR does 3 things:
>> 
>> * Adds a port of ZGC's MRSW mutex (see [0]) to Hotspot
>> * Adds some new utilities for writing multi-threaded tests.
>> * Adds some tests for MRSW Mutex using these new utilities
>> 
>> The ticket has some comments which might be worth checking out: https://bugs.openjdk.org/browse/JDK-8291714
>> 
>> [0] Original source code here: https://github.com/openjdk/zgc/blob/zgc_generational/src/hotspot/share/gc/z/zJNICritical.cpp
>
> Johan Sjölén has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review comments

I don't expect this to be a popular opinion, but the more I think about it
the less I like the direct use of PlatformMonitor here rather than using
Monitor.  The "extra cruft" that comes with Monitor is there for reasons, and
I'm not convinced that bypassing all that is good.

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PR: https://git.openjdk.org/jdk/pull/9838