RFR: 8347408: Create an internal method handle adapter for system calls with errno [v7]
Per Minborg
pminborg at openjdk.org
Mon Jan 13 11:07:11 UTC 2025
> 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.explicitFail avgt 30 42.061 ? 1.261 ns/op
> CaptureStateUtilBench.explicitSuccess avgt 30 23.142 ? 0.739 ns/op
> CaptureStateUtilBench.tlFail avgt 30 23.580 ? 0.267 ns/op
> CaptureStateUtilBench.tlSuccess avgt 30 1.753 ? 0.016 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 >10x improvement on the happy path.
>
>
> Tested and passed tiers 1-3.
Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
Update benchmark and micro optimize
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/22391/files
- new: https://git.openjdk.org/jdk/pull/22391/files/f128c912..fe12661a
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=22391&range=06
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=22391&range=05-06
Stats: 6 lines in 2 files changed: 3 ins; 1 del; 2 mod
Patch: https://git.openjdk.org/jdk/pull/22391.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/22391/head:pull/22391
PR: https://git.openjdk.org/jdk/pull/22391
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