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:
> 
> ![image](https://github.com/user-attachments/assets/3cf122bb-0ed6-4dd6-ab6d-dcada0147efb)
> 
> 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


More information about the core-libs-dev mailing list