RFR: 8347408: Create an internal method handle adapter for system calls with errno [v14]
Per Minborg
pminborg at openjdk.org
Wed Jan 15 16:09:36 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.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.
Per Minborg has updated the pull request incrementally with two additional commits since the last revision:
- Use invokeExact semantics in the tests
- Clean up
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/22391/files
- new: https://git.openjdk.org/jdk/pull/22391/files/69fff386..410508ed
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=22391&range=13
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=22391&range=12-13
Stats: 21 lines in 2 files changed: 4 ins; 4 del; 13 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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