On Tue, 26 Nov 2024 15:04:51 GMT, Per Minborg <[email protected]> wrote:
> Going forward, converting older JDK code to use the relatively new FFM API
> requires system calls that can provide `errno` and the likes to explicitly
> allocate a MemorySegment to capture potential error states. This can lead to
> negative performance implications if not designed carefully and also
> introduces unnecessary code complexity.
>
> Hence, this PR proposes to add a _JDK internal_ method handle adapter that
> can be used to handle system calls with `errno`, `GetLastError`, and
> `WSAGetLastError`.
>
> It currently relies on a thread-local cache of MemorySegments to allide
> allocations. If, in the future, a more efficient thread-associated allocation
> scheme becomes available, we could easily migrate to that one.
>
> Tested and passed tiers 1-3.
src/java.base/share/classes/jdk/internal/foreign/CaptureStateUtil.java line 50:
> 48: private static final long SIZE =
> Linker.Option.captureStateLayout().byteSize();
> 49:
> 50: private static final TerminatingThreadLocal<MemorySegment> TL = new
> TerminatingThreadLocal<>() {
TerminatingThreadLocal is carrier-local so the usage here will require a
detailed walk through to make sure that a virtual thread cannot be preempted
when it has access to this memory segment.
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PR Review Comment: https://git.openjdk.org/jdk/pull/22391#discussion_r1910094423
