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

[Johan Sjölén]

On Wed, 17 Aug 2022 13:14:34 GMT, David Holmes <dholmes at openjdk.org> wrote:

>>> > Multi-Reader Single-Writer mutex
>>> 
>>> Sorry to bikeshed but such a thing is called a ReadWriteLock or a ReadersWriterLock or something similar - can we please use familiar nomenclature here (even rwlock as per POSIX). "mutex" is a contraction of mutual-exclusion and as readers are not mutually exclusive it is an oxymoron to talk about a "multi-reader mutex". Thanks.
>> 
>> For what it's worth, C++ Standard Library uses "mutex" to refer to an object
>> that gets locked, and uses "lock" to refer to an RAII object that locks a
>> "mutex". So it has, for example, `std::shared_mutex`, which is
>> multi-reader/single-writer. The idea being that a "mutex" provides some kind
>> of mutual exclusion - in the case of shared_mutex readers (multiple) are
>> excluded from any writer, and writers are exclusive from each other. I'd
>> prefer that to calling these new things "locks".
>
>> For what it's worth, C++ Standard Library uses "mutex" to refer to an object that gets locked, and uses "lock" to refer to an RAII object that locks a "mutex".
> 
> So their "lock" would be our MutexLocker? The far more dominant terminology is that a mutex is a lock.

Thank you for the additional review, @dholmes-ora . I fixed those and added some more documentation.

The changes to `threadHelper.inline.hpp` is being merged through a separate patch (see JDK-8292679, https://github.com/openjdk/jdk/pull/9962), and so are not in need of review.

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