On Wed, 12 Feb 2025 16:04:53 GMT, Per Minborg <pminb...@openjdk.org> 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 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:
>>
>>
>> Benchmark Mode Cnt Score
>> Error Units
>> CaptureStateUtilBench.OfVirtual.adaptedSysCallFail avgt 30 24.193
>> ? 0.268 ns/op
>> CaptureStateUtilBench.OfVirtual.adaptedSysCallSuccess avgt 30 8.268
>> ? 0.080 ns/op
>> CaptureStateUtilBench.OfVirtual.explicitAllocationFail avgt 30 42.076
>> ? 1.003 ns/op
>> CaptureStateUtilBench.OfVirtual.explicitAllocationSuccess avgt 30 21.801
>> ? 0.138 ns/op
>> CaptureStateUtilBench.OfVirtual.tlAllocationFail avgt 30 23.265
>> ? 0.087 ns/op
>> CaptureStateUtilBench.OfVirtual.tlAllocationSuccess avgt 30 8.285
>> ? 0.155 ns/op
>>
>> CaptureStateUtilBench.adaptedSysCallFail avgt 30 23.033
>> ? 0.423 ns/op
>> CaptureStateUtilBench.adaptedSysCallSuccess avgt 30 3.676
>> ? 0.104 ns/op // <- Happy path using an internal pool
>>
>> CaptureStateUtilBench.explicitAllocationFail avgt 30 42.023
>> ? 0.736 ns/op
>> CaptureStateUtilBench.explicitAllocationSuccess avgt 30 22.013
>> ? 0.648 ns/op // <- Allocating memory upon each invocation
>>
>> CaptureStateUtilBench.tlAllocationFail avgt 30 22.050
>> ? 0.233 ns/op
>> CaptureStateUtilBench.tlAllocationSuccess avgt 30 3.756
>> ? 0.056 ns/op // <- Using the pool explicitly from Java code
>>
>>
>> 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); // ...
>
> Per Minborg has updated the pull request incrementally with one additional
> commit since the last revision:
>
> Add holding a reference to the original arena in the taken arena
Unfortunately, this PR would evolve in a direction that is hard to maintain if
appropriate changes were made to cover some virtual thread corner cases. So, we
need to rethink the overall solution and come back with another PR. Thanks for
your feedback so far.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/23517#issuecomment-2656315310
