RFR: 8360025: (se) Convert kqueue Selector Implementation to use FFM APIs [v4]

[Darragh Clarke]

On Thu, 28 Aug 2025 08:51:14 GMT, Darragh Clarke <dclarke at openjdk.org> wrote:

>> This PR aims to Panamize the Java Kqueue implementation, This is based on the work that was previously shared in https://github.com/openjdk/jdk/pull/22307 , The main change since then is that this branch takes advantage of the changes made in https://github.com/openjdk/jdk/pull/25043 to allow for better performance during errno handling.
>> 
>> These changes feature a lot of Jextract generated files, though alterations have been made in relation to Errno handling and performance improvements.
>> 
>> I will update this description soon to include performance metrics on a few microbenchmarks, though currently it's roughly 2% to 3% slower with the changes, which is somewhat expected, though there are still a few ideas of possible performance improvements that could be tried. Any suggestions or comments in that area are more than welcome however.
>
> Darragh Clarke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:
> 
>  - fixed copyright header
>  - merged master into branch
>  - moved repeating code into own method
>  - implementing feedback, adding missing errno checks, cleanup
>  - feedback
>  - general cleanup
>  - small refactoring
>  - Performance
>  - implementing feedback
>  - removed unrelated change
>  - ... and 2 more: https://git.openjdk.org/jdk/compare/e949c2ca...cc5f558a

Thanks for the thorough review, I'll address all these in the next commit.
As for the changes to generated code, I'll draft up a list of what changed and why, though FFMUtils in particular came about as trying to move reusable utility methods into a shared place to cut down on code duplication going forward

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PR Comment: https://git.openjdk.org/jdk/pull/25546#issuecomment-3233869851