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

[Alan Bateman]

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/1fc9f3a2...cc5f558a

src/java.base/macosx/classes/sun/nio/ch/KQueue.java line 120:

> 118:             // rest default to zero
> 119: 
> 120:             // this do-while replaces restartable

Future maintainers may ask what "replaces restartable" means, I think better to say that it calls kqueue if the syscall is interrupted (EINTR).

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PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307431006