On Thu, 13 Mar 2025 15:21:33 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 ove...
>
> Per Minborg has updated the pull request with a new target base due to a
> merge or a rebase. The pull request now contains 34 commits:
>
> - Merge master
> - Add test for woven allocation
> - Merge branch 'master' into errno-util3
> - Use lazy initialization of method handles
> - Clean up visibility
> - Merge branch 'master' into errno-util3
> - Add @ForceInline annotations
> - Add out of order test for VTs
> - Allow memory reuse for several arenas
> - Remove file
> - ... and 24 more: https://git.openjdk.org/jdk/compare/4e51a8c9...6d782a84
src/java.base/share/classes/jdk/internal/foreign/CaptureStateUtil.java line 65:
> 63: // returnType in {int.class | long.class}
> 64: // stateName can be anything non-null but should be in
> {"GetLastError" | "WSAGetLastError"} | "errno")}
> 65: private record BasicKey(Class<?> returnType, String stateName) {
Please at least add an `hashCode` - this avoids a hefty overhead from code
generation in ObjectMethods.bootstrap, unavoidable whenever we put entries into
a hash map.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23765#discussion_r2056408940
