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

[Per Minborg]

On Sat, 31 May 2025 02:07:40 GMT, Chen Liang <liach 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.
>
> src/java.base/share/classes/jdk/internal/ffi/util/FFMUtils.java line 26:
> 
>> 24:  */
>> 25: 
>> 26: package jdk.internal.ffi.util;
> 
> If this is some general ffm utils for using ffm, you can put it in jdk.internal.foreign.

These methods are only intended to be used for "panamization" and are not for general use. So, this is the reason we propose to have them here. But maybe some of them might be of general interest?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2121790738