On Thu, 23 Mar 2023 10:28:23 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> Yes - although there is a distinction between passed by value and by ref. I
>> wouldn't be surprised if we just threw NPE for by-value.
>
> Just did a test with jshell:
>
>
> jshell> Linker linker = Linker.nativeLinker();
>
> jshell> MethodHandle handleValue =
> linker.downcallHandle(FunctionDescriptor.ofVoid(MemoryLayout.structLayout(ValueLayout.JAVA_INT)));
> handleValue ==> MethodHandle(MemorySegment,MemorySegment)void
>
> jshell> handleValue.invoke(MemorySegment.ofAddress(1), null);
> | Exception java.lang.NullPointerException
> | at (#5:1)
>
>
> So, yes, passing `null` for a "by-value" struct issues NPEs. I also get same
> exception when calling a method handle which passes a struct by reference:
>
>
> jshell> MethodHandle handleRef =
> linker.downcallHandle(FunctionDescriptor.ofVoid(ValueLayout.ADDRESS));
> handleRef ==> MethodHandle(MemorySegment,MemorySegment)void
>
> jshell> handleRef.invoke(MemorySegment.ofAddress(1), null);
> | Exception java.lang.NullPointerException
> | at (#7:1)
>
>
> Given what the impl does, to be fair I don't mind the NPE (it seems a good
> exception to throw if we're passing a raw `null`). But we should document it
> at such.
>
> It also seems like the first parameter of the downcall has somewhat better
> checks (but still NPEs):
>
>
> jshell> handleRef.invoke(null, MemorySegment.ofAddress(1));
> | Exception java.lang.NullPointerException
> | at Objects.requireNonNull (Objects.java:233)
> | at SharedUtils.checkSymbol (SharedUtils.java:351)
> | at (#8:1)
>
>
> And:
>
>
> jshell> handleRef.invoke(MemorySegment.NULL, MemorySegment.ofAddress(1));
> | Exception java.lang.IllegalArgumentException: Symbol is NULL:
> MemorySegment{ heapBase: Optional.empty address:0 limit: 0 }
> | at SharedUtils.checkSymbol (SharedUtils.java:353)
> | at (#9:1)
>
>
> I think this last case is the _only_ one where IAE is warranted - as the role
> of the first parameter is special, and we can't tolerate a
> `MemorySegment::NULL` there. For all other reference parameters, the downcall
> handle should just check that they are non-null, and throw if so.
The returned method handle will throw an {@link IllegalArgumentException} if
the {@link MemorySegment}
representing the target address of the foreign function is the {@link
MemorySegment#NULL} address.
The returned method handle will additionally throw {@link NullPointerException}
if any parameter of type {@link MemorySegment} is {@code null}.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/13079#discussion_r1145982159
