RFR: 8276663: Cleanup NMT AccessLock [v2]

[David Holmes]

On Fri, 5 Nov 2021 02:15:33 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Please review this cleanup patch to NMT AccessLock:
>> 
>> * Make LockState enum private, no external use.
>> * const lock location pointer
>> * Use memory_order_relaxed for lock counter updates.
>> 
>> Test:
>> - [x] hotspot_nmt on x86_64 and aarch64
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Uses Atomic::load()

To clarify a writeLock needs acquire on lock and release on unlock; the readLock only needs acquire on lock.

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PR: https://git.openjdk.java.net/jdk/pull/6267