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/6924a084...cc5f558a

src/java.base/macosx/classes/jdk/internal/ffi/generated/ErrnoUtils.java line 26:

> 24:  */
> 25: 
> 26: package jdk.internal.ffi.generated;

Using jdk.internal.ffi.generated.** for jextract generated code is good. I'm not sure this is the right place for ErrnoUtils.

src/java.base/macosx/classes/jdk/internal/ffi/generated/ErrnoUtils.java line 42:

> 40:     private static final long ERRNO_STRING_HOLDER_ARRAY_SIZE = 256L;
> 41: 
> 42:     public static IOException IOExceptionWithErrnoString(int errno, String message) {

The naming is a bit confusing here, minimally need a method description so we can quickly understand the relationship between "message" and strerror(errno).

src/java.base/macosx/classes/sun/nio/ch/KQueue.java line 48:

> 46: final class KQueue {
> 47: 
> 48:     private static final BufferStack POOL = BufferStack.of(timespec.layout());

I think we'll need to rename this to BUFFER_STACK or something better as "POLL" is a bit confusing.

src/java.base/macosx/classes/sun/nio/ch/KQueue.java line 91:

> 89:      */
> 90:     static MemorySegment getEvent(MemorySegment memoryHandle, int i) {
> 91:         return kevent.asSlice(memoryHandle, i);

Previous work eliminated allocating from the performance critical usages, might have to check the implications of asSlice here.

src/java.base/macosx/classes/sun/nio/ch/KQueue.java line 111:

> 109:     // -- Native methods --
> 110: 
> 111:     static public int register(int kqfd, int fd, int filter, int flags) {

No need to make this public.

src/java.base/macosx/classes/sun/nio/ch/KQueue.java line 113:

> 111:     static public int register(int kqfd, int fd, int filter, int flags) {
> 112:         int result;
> 113:         try (Arena arena = Arena.ofConfined()) {

The register method is very performance critical (the equivalents on Linux might be called >1M/sec) so need to see the impact of creating a confined arena and allocating.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307400147
PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307403262
PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307408362
PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307411960
PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307414172
PR Review Comment: https://git.openjdk.org/jdk/pull/25546#discussion_r2307419308