RFR: 8332003: Clarify javadoc for MemoryLayout::offsetHandle [v2]

[Paul Sandoz]

On Thu, 9 May 2024 18:26:17 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Consider this layout:
>> 
>> 
>> MemoryLayout SEQ = MemoryLayout.sequenceLayout(5,
>>              MemoryLayout.sequenceLayout(10, JAVA_INT));
>> 
>> 
>> And the corresponding offset handle:
>> 
>> 
>> MethodHandle offsetHandle = SEQ.offsetHandle(PathElement.sequenceLayout(), PathElement.sequenceLayout());
>> 
>> 
>> The resulting method handle takes two additional `long` indices. The implementation checks that the dynamically provided indices conform to the bound available at construction: that is, the first index must be < 5, while the second must be < 10. If this is not true, an `IndexOutOfBoundException` is thrown.
>> 
>> However, the javadoc for `MemoryLayout::byteOffsetHandle` doesn't claim anything in this direction. There are only some vague claims in the javadoc for `PathElement::sequenceElement()` and `PathElement::sequenceElement(long, long, long)` which make some claims on which indices are actually allowed, but the text seems more in the tone of a discussion, rather than actual normative text.
>> 
>> I've tweaked the javadoc for `MemoryLayout::byteOffsetHandle` to actually state that the indices will be checked against the "size" of the corresponding open path element (this is a new concept that I also have defined in the javadoc).
>> 
>> I also added a test for `byteOffsetHandle` as I don't think we had a test for that specifically (although this method is tested indirectly, via `MemoryLayout::varHandle`).
>
> Maurizio Cimadamore has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Update copyright
>  - Add javadoc to other MemoryLayout methods returning VarHandle/MethodHandle to describe which exception can be thrown by returned handle

src/java.base/share/classes/java/lang/foreign/MemoryLayout.java line 574:

> 572:      * {@code c_1}, {@code c_2}, ... {@code c_m} are other <em>static</em> offset
> 573:      * constants (such as field offsets) which are derived from the layout path.
> 574:      * <p>

Can we connected back to the prior paragraph? e.g., for any given dynamic argument `x_n`, the index into the sequence associated with the n'th open path element whose size is `size_n`,`x_n` must be `>= 0` or `< size_n`

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PR Review Comment: https://git.openjdk.org/jdk/pull/19158#discussion_r1595836040