RFR: 8291555: Implement alternative fast-locking scheme [v62]

[Roman Kennke]

On Mon, 24 Apr 2023 22:51:10 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove unnecessary comments
>
> src/hotspot/cpu/arm/macroAssembler_arm.cpp line 1803:
> 
>> 1801: #ifdef ASSERT
>> 1802:   // Poison scratch regs
>> 1803:   POISON_REGS((~savemask), t1, t2, t3, 0x10000001);
> 
> Should this poison value be: 0x20000002

Why?

> src/hotspot/share/logging/logTag.hpp line 80:
> 
>> 78:   LOG_TAG(exceptions) \
>> 79:   LOG_TAG(exit) \
>> 80:   LOG_TAG(fastlock2) \
> 
> So why 'fastlock2'? Where's 'fastlock1'? Or 'fastlock'?

It's currently only used in the arm port. I'm changing it to 'fastlock', ok?

> src/hotspot/share/runtime/arguments.cpp line 1994:
> 
>> 1992:   if (UseHeavyMonitors) {
>> 1993:     FLAG_SET_CMDLINE(LockingMode, LM_MONITOR);
>> 1994:   }
> 
> HotSpot option processing has a general rule of last setting wins.
> With L1992-1994 here, I think there might be a problem with a cmd
> line that specifies:
> 
>     -XX:+UseHeavyMonitors -XX:LockingMode=1
> 
> I think that the resulting value of `LockingMode` will be `LM_MONITOR`
> instead of `LM_LEGACY`. Granted mixing uses of `UseHeavyMonitors`
> with `LockingMode` is just asking for trouble...

I added a check that rejects conflicting +UseHeavyMonitors and LockingMode=X flags on the cmd line. UseHeavyMonitors is already deprecated, and with the new LockingMode flag should be removed asap (in a follow-up PR).

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1178244295
PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1178253708
PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1178260893