Speed optimization for .NET 9.0+ through System.Threading.Lock

[MarkCiliaVincenti]

No description provided.

[bitfaster]

I have added a net9 build target with automated tests - you can merge master into your changes to get this.

Because System.Threading.Lock is only available on net9, you will need to make this change only for the net9 target using preprocessor directives, you can see a similar example for the lock statement in ConcurrentLfu here #697.

[MarkCiliaVincenti]

Merged. The preprocessor directives are not needed because this is using a source-generated polyfill.

[coveralls]

coverage: 99.062%. first build
when pulling ee89e00 on MarkCiliaVincenti:SystemThreadingLock
into 422ab25 on bitfaster:main.

[MarkCiliaVincenti]

@bitfaster ?

[MarkCiliaVincenti]

Are you still interested in this PR @bitfaster?

[bitfaster]

Sorry did not get a chance to come back to this earlier.

In this library I would prefer to keep all preprocessor manipulation explicit to avoid accidental perf implications, so would prefer not to add tools that implicitly inject different code. Can you do the same change explicitly?

[MarkCiliaVincenti]

I'm not sure I understand. Can you please give examples of what changes you need?