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

[Roman Kennke]

On Fri, 24 Mar 2023 06:55:55 GMT, David Holmes <dholmes 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
>
> src/hotspot/share/runtime/threads.cpp line 1422:
> 
>> 1420: }
>> 1421: 
>> 1422: JavaThread* Threads::owning_thread_from_object(ThreadsList * t_list, oop obj) {
> 
> Is this thread-safe?

My last commit changed that code to only run during safepoints. It should be safe now, and I added an assert that verifies that it is only run at safepoint.

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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1150401225