On Tue, 25 Feb 2025 08:27:26 GMT, Per Minborg <pminb...@openjdk.org> wrote:
> As we advance, 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 adding a JDK internal method handle adapter that can
> be used to handle system calls with `errno`, `GetLastError`, and
> `WSAGetLastError`.
>
> It relies on an efficient carrier-thread-local cache of memory regions to
> allide allocations.
>
>
> Here are some benchmarks that ran on a platform thread and virtual threads
> respectively (M1 Mac):
>
>
> Benchmark Mode Cnt Score
> Error Units
> CaptureStateUtilBench.OfVirtual.adaptedSysCallFail avgt 30 24.330
> ? 0.820 ns/op
> CaptureStateUtilBench.OfVirtual.adaptedSysCallSuccess avgt 30 8.257
> ? 0.117 ns/op
> CaptureStateUtilBench.OfVirtual.explicitAllocationFail avgt 30 41.415
> ? 1.013 ns/op
> CaptureStateUtilBench.OfVirtual.explicitAllocationSuccess avgt 30 21.720
> ? 0.463 ns/op
> CaptureStateUtilBench.OfVirtual.tlAllocationFail avgt 30 23.636
> ? 0.182 ns/op
> CaptureStateUtilBench.OfVirtual.tlAllocationSuccess avgt 30 8.234
> ? 0.156 ns/op
> CaptureStateUtilBench.adaptedSysCallFail avgt 30 23.918
> ? 0.487 ns/op
> CaptureStateUtilBench.adaptedSysCallSuccess avgt 30 4.946
> ? 0.089 ns/op
> CaptureStateUtilBench.explicitAllocationFail avgt 30 42.280
> ? 1.128 ns/op
> CaptureStateUtilBench.explicitAllocationSuccess avgt 30 21.809
> ? 0.413 ns/op
> CaptureStateUtilBench.tlAllocationFail avgt 30 24.422
> ? 0.673 ns/op
> CaptureStateUtilBench.tlAllocationSuccess avgt 30 5.182
> ? 0.152 ns/op
>
>
> Adapted system call:
>
> return (int) ADAPTED_HANDLE.invoke(0, 0); // Uses a MH-internal pool
> ```
> Explicit allocation:
>
> try (var arena = Arena.ofConfined()) {
> return (int) HANDLE.invoke(arena.allocate(4), 0, 0);
> }
> ```
> Thread Local allocation:
>
> try (var arena = POOLS.take()) {
> return (int) HANDLE.invoke(arena.allocate(4), 0, 0); // Uses a
> manually specified pool
> }
> ```
> The adapted system call exhibits a ~4x performance improvement over the
> existing "explicit allocation" scheme for the happy path on platform threads.
> ...
This pull request has been closed without being integrated.
-------------
PR: https://git.openjdk.org/jdk/pull/23765
