RFR: 8323724: Remove potential re-inflation from FastHashCode under LM_LIGHTWEIGHT

[Fredrik Bredberg]

On Wed, 24 Apr 2024 16:18:25 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> There is a race when a thread that tries to install the hash code finds an inflated `ObjectMonitor`, which the deflation thread is concurrently deflating, thus causing the `FastHashCode` logic to re-inflate the `ObjectMonitor`.
>> 
>> This PR solves that by simply taking the ObjectMonitor pointer from the markWord and retrying without inflating, if it was deflated.
>> 
>> This enhancement will remove the last code path which can inflate an `ObjectMonitor` from a non java thread, which in turn will simplify the `is_lock_owned` logic and allow for stronger assertions.
>> 
>> Tested and passes tier1-tier5 ok.
>
>>This enhancement will remove the last code path which can inflate an ObjectMonitor from a non java thread, which in turn will simplify the is_lock_owned logic and allow for stronger assertions.
> 
> Is there an RFE for this?  It looks like a good cleanup.

@coleenp 
> Is there an RFE for this? It looks like a good cleanup.

Do you think I should create a RFE for this, before integrating this PR?

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PR Comment: https://git.openjdk.org/jdk/pull/18876#issuecomment-2090402428