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

[Roman Kennke]

On Fri, 24 Mar 2023 06:16:14 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/arguments.cpp line 1997:
> 
>> 1995:   }
>> 1996:   if (UseHeavyMonitors) {
>> 1997:     FLAG_SET_DEFAULT(UseFastLocking, false);
> 
> Probably should be an error if both are set on the command-line.

I am not sure. UseFastLocking (or whatever we will call it in the near future) chooses between traditional and new stack-locking. We disable both by +UseHeavyMonitors. Also, +UseFastLocking is not really meant to be used by users, at least it is my intention to mainly turn it on programatically it when compact headers (Lilliput) is turned on. When also running with +UseHeavyMonitors, then it doesn't really matter which stack-locking impl is selected, neither would actually be used. I'd rather remove the explicit turning-off of UseFastMonitors under +UseHeavyMonitors.

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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1149623912