RFR: 8291555: Implement alternative fast-locking scheme [v29]

[Roman Kennke]

On Thu, 23 Mar 2023 16:32:57 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'origin/JDK-8291555-v2' into JDK-8291555-v2
>>  - Set condition flags correctly after fast-lock call on aarch64
>
> Is anybody familiar with the academic literature on this topic? I am sure I am not the first person which has come up with this form of locking. Maybe we could use a name that refers to some academic paper?

> @rkennke Question about ZGC and LockStack::contains(): how does this work with colored pointers? Don't we have to mask the color bits out somehow when comparing? E.g. using `ZAddress::offset()` ?

That would be a question for @fisk and/or @stefank. AFAIK, the color bits should be masked by ZGC barriers *before* the oops enter the synchronization subsystem. But I kinda suspect that we are somehow triggering a ZGC bug here. Maybe we require barriers when reading oops from the lock-stack too?

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PR Comment: https://git.openjdk.org/jdk/pull/10907#issuecomment-1485390285