Re: RFR: 8347408: Create an internal method handle adapter for system calls with errno [v3]

[Shaojin Wen]

On Mon, 5 May 2025 17:13:02 GMT, Per Minborg <pminb...@openjdk.org> wrote:

>> As we advance, 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 adding 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.
>
> Per Minborg has updated the pull request incrementally with three additional 
> commits since the last revision:
> 
>  - Fix empty line at the end of a third file
>  - Fix empty line at the end of another file
>  - Fix empty line at the end of a file

src/java.base/share/classes/jdk/internal/foreign/CaptureStateUtil.java line 390:

> 388:                 return MhUtil.findVirtual(LOOKUP, Arena.class, "close",
> 389:                         MethodType.methodType(void.class));
> 390:         }

Suggestion:

        return switch (index) {
            case NON_NEGATIVE_INT -> MhUtil.findStatic(LOOKUP, "nonNegative",
                    MethodType.methodType(boolean.class, int.class));
            case SUCCESS_INT -> MhUtil.findStatic(LOOKUP, "success",
                    MethodType.methodType(int.class, int.class, 
MemorySegment.class));
            case ERROR_INT -> MhUtil.findStatic(LOOKUP, "error",
                    MethodType.methodType(int.class, MethodHandle.class, 
int.class, MemorySegment.class));
            case NON_NEGATIVE_LONG -> MhUtil.findStatic(LOOKUP, "nonNegative",
                    MethodType.methodType(boolean.class, long.class));
            case SUCCESS_LONG -> MhUtil.findStatic(LOOKUP, "success",
                    MethodType.methodType(long.class, long.class, 
MemorySegment.class));
            case ERROR_LONG -> MhUtil.findStatic(LOOKUP, "error",
                    MethodType.methodType(long.class, MethodHandle.class, 
long.class, MemorySegment.class));
            case ACQUIRE_ARENA -> MhUtil.findStatic(LOOKUP, "acquireArena",
                    MethodType.methodType(Arena.class));
            case ALLOCATE -> MhUtil.findStatic(LOOKUP, "allocate",
                    MethodType.methodType(MemorySegment.class, Arena.class));
            case ARENA_CLOSE -> MhUtil.findVirtual(LOOKUP, Arena.class, "close",
                    MethodType.methodType(void.class));
            default -> throw new InternalError("Unknown index: " + index);
        };

Switch statement can be replaced with enhanced 'switch'

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25043#discussion_r2075016584