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.
>
> Here are some benchmarks:
>
>
> Benchmark Mode Cnt Score Error
> Units
> CaptureStateUtilBench.explicitAllocationFail avgt 30 41.615 ? 1.203
> ns/op
> CaptureStateUtilBench.explicitAllocationSuccess avgt 30 23.094 ? 0.580
> ns/op
> CaptureStateUtilBench.threadLocalFail avgt 30 14.760 ? 0.078
> ns/op
> CaptureStateUtilBench.threadLocalReuseSuccess avgt 30 7.189 ? 0.151
> ns/op
>
>
> Explicit allocation:
>
> try (var arena = Arena.ofConfined()) {
> return (int) HANDLE.invoke(arena.allocate(4), 0, 0);
> }
>
>
> Thread Local (tl):
>
> return (int) ADAPTED_HANDLE.invoke(arena.allocate(4), 0, 0);
>
>
> The graph below shows the difference in latency for a successful call:
>
> 
>
> This is a ~3x improvement for both the happy and the error path.
>
>
> Tested and passed tiers 1-3.
This pull request has been closed without being integrated.
-------------
PR: https://git.openjdk.org/jdk/pull/22391
