RFR: 8319773: Avoid inflating monitors when installing hash codes for LM_LIGHTWEIGHT [v2]

[David Holmes]

On Mon, 13 Nov 2023 07:29:40 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> src/hotspot/share/runtime/synchronizer.cpp line 582:
>> 
>>> 580:           // It can only have installed an anonymously locked monitor at this point.
>>> 581:           // Fetch that monitor, set owner correctly to this thread, and
>>> 582:           // exit it (allowing waiting threads to enter).
>> 
>> I don't understand why the anonymous owner case is no longer being checked. ??
>
> The condition does now check for a successful CAS, not the unsuccessful one. If it was successful then there is no monitor, thus no anonymous owner.
> 
> If the CAS failed and the mark word is no longer fast locked. It must be inflated. So we fallthrough down to the inflated case.
> 
> `ObjectSynchronizer::inflate` correctly handles fixing the owner.

I see - thanks. It is hard to see where the code goes to when the CAS fails.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16603#discussion_r1391043625