RFR: 8321786: SegmentAllocator:allocateFrom(ValueLayout, MemorySegment, ValueLayout, long, long) spec mismatch in exception scenario [v4]

[Maurizio Cimadamore]

On Tue, 12 Dec 2023 13:58:42 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Revert change in allocateNoInit
>
> src/java.base/share/classes/java/lang/foreign/SegmentAllocator.java line 396:
> 
>> 394:      * @throws IllegalArgumentException if {@code elementCount * sourceElementLayout.byteSize()} overflows
>> 395:      * @throws IndexOutOfBoundsException if {@code sourceOffset > source.byteSize() - (elementCount * sourceElementLayout.byteSize())}
>> 396:      * @throws IndexOutOfBoundsException if either {@code sourceOffset} or {@code elementCount} are {@code < 0}
> 
> I think that if elementCount < 0, we should throw IAE, not IOOBE. Note that we explain this method as:
> 
>  MemorySegment dest = this.allocate(elementLayout, elementCount);
>  MemorySegment.copy(source, sourceElementLayout, sourceOffset, dest, elementLayout, 0, elementCount);
> 
> 
> So, the set of exceptions thrown by these two methods should be preserved. This means that `allocate(MemoryLayout, long)` gets a first pass at checking - this means IAE for overflows and also for negative element count.
> 
> After that, the exceptions we can have are those specified in MemorySegment.copy.

(as we did in other patches, I think it's important here to remain true to the semantics of the "desugared" code, because that will guarantee that developers can refactor their code w/o worrying about exceptions changing from under them)

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PR Review Comment: https://git.openjdk.org/jdk/pull/17079#discussion_r1424034360