RFR: 8367982: Unify ObjectSynchronizer and LightweightSynchronizer

[Fredrik Bredberg]

On Thu, 23 Oct 2025 12:06:28 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> This is the last PR in a series of PRs (see: [JDK-8344261](https://bugs.openjdk.org/browse/JDK-8344261)) to obsolete the LockingMode flag and related code.
>> 
>> The main focus is to to unify `ObjectSynchronizer` and `LightweightSynchronizer`.
>> There used to be a number of "dispatch functions" to redirect calls depending on the setting of the `LockingMode` flag.
>> Since we now only have lightweight locking, there is no longer any need for those dispatch functions, so I removed them.
>> To remove the dispatch functions I renamed the corresponding lightweight functions and call them directly.
>> This ultimately led me to remove "lightweight" from the function names and go back to "fast" instead, just to avoid having some with, and some without the "lightweight" part of the name.
>> 
>> This PR also include a small simplification of `ObjectSynchronizer::FastHashCode`.
>> 
>> Tested tier1-7 (on supported platforms) without seeing any problems that can be traced to this code change.
>> All other platforms (`arm`, `ppc`, `riscv`, `s390`) has been sanity checked using QEMU.
>
> Thanks for cleaning this up on all platforms! Works on PPC64.
> Indentation could be improved at many places where the next line was aligned (all platforms and shared code).

@TheRealMDoerr, @RealFYang 
> Indentation could be improved at many places where the next line was aligned (all platforms and shared code).

Oops, my bad. Guess this what you end up with when you use `bash`, `grep -r` and `sed` to seek out and remove "lightweight" from a source tree, and then check the result using old Un*x style `diff -w`. I think all the faulty indentation stuff is fixed now, and yes I did check with "new" style `git diff` to see the surrounding lines.

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PR Comment: https://git.openjdk.org/jdk/pull/27915#issuecomment-3443454592