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

[Per Minborg]

On Tue, 14 Oct 2025 10:38:01 GMT, Darragh Clarke <dclarke at openjdk.org> wrote:

> This PR was originally part of #25546, though that PR has been split in 2, the first chunk was https://github.com/openjdk/jdk/pull/27590.
> 
> This PR aims to convert KQueue to use FFM apis, the first PR in this area added all the jextract generated code needed, while this PR modifies some of the jextract code and then uses it with Kqueue.
> 
> A brief rundown of the changes:
> - The files `errno_h$shared.java` , `kqueue_h$shared.java`, `timespec_h$shared.java` and `timespec_h.java` have all been deleted. This is because they all contained shared elements that could be moved into the Utility file `FFMUtils.java`
> - `Kqueue.c` has been deleted, and all native methods in the other `KQueue` files have been replaced with references to the generated files kevent and kqueue. This is the bulk of the changes
> - Both the `Kqueue()` and `Kevent()` methods in `kqueue_h.java`  were modified to use adapted method handles that will return the errno value

src/java.base/macosx/classes/jdk/internal/ffi/generated/kqueue/kqueue_h.java line 134:

> 132:     public static int kqueue() {
> 133:         try {
> 134:             return (int) kqueue.ADAPTED.invokeExact();

No tracing?

src/java.base/macosx/classes/jdk/internal/ffi/generated/kqueue/kqueue_h.java line 152:

> 150: 
> 151:         public static final MemorySegment ADDR = FFMUtils.findOrThrow("kevent");
> 152:         public static final MethodHandle HANDLE = Linker.nativeLinker().downcallHandle(ADDR, DESC,

I would suspect we do not use `ADDR` and `HANDLE` so maybe we do not have to store them?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/27796#discussion_r2428738328
PR Review Comment: https://git.openjdk.org/jdk/pull/27796#discussion_r2428735537