[foreign-memaccess] RFR: 8252504: Add a method to MemoryLayout which returns a offset-computing method handle

[Jorn Vernee]

On Thu, 19 Nov 2020 17:26:32 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This PR adds two new methods: `bitOffsetHandle` and `byteOffsetHandle` to `MemoryLayout`, that can be used to create method handles that can compute the effective offset of a layout element given a set of additional `long` indexes.
>> 
>> I also cleaned up a leftover in the javadoc of bitOffset and byteOffset where an API note was stating that `sequenceElement()` layout path elements would be interpreted as `sequenceElement(0)`, but they were actually being rejected outright (as they should).
>> 
>> I also added some tests to cover the corner case where an UnsupportedOperationException was being thrown. (some of the churn in the tests is from introducing static imports. I hope it's not too noisy).
>
> test/jdk/java/foreign/TestLayoutPaths.java line 436:
> 
>> 434:         return new Object[][]{
>> 435:             {
>> 436:                 MemoryLayout.ofSequence(10, JAVA_INT),
> 
> The test is good, but there's no case which features more than one long index. I think it is worth adding at least a few, since that's where all the combination logic (and ordering) can go wrong?

Yes, makes sense. Thanks for the suggestion.

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PR: https://git.openjdk.java.net/panama-foreign/pull/396