[foreign-memaccess] RFR 8236267: Cleanup support for layouts with undefined size

[Maurizio Cimadamore]

Another update:

http://cr.openjdk.java.net/~mcimadamore/panama/8236267_v3

I've rewritten all the layout path-accepting methods to use a common 
implementation routine. This also helped shaking out an issue in a test 
(TestLayoutPaths::testBadSequencePathInOffset) which was expecting a 
failure on a correct path element (MemoryLayout::offset() should only 
choke on unspecified sequence element selections).

Maurizio

On 07/01/2020 12:47, Maurizio Cimadamore wrote:
> Updated webrev here:
>
> http://cr.openjdk.java.net/~mcimadamore/panama/8236267_v2/
>
> Cheers
> Maurizio
>
> On 19/12/2019 14:52, Maurizio Cimadamore wrote:
>> Hi,
>> I decided to go ahead and create a separate issue for dealing with 
>> unbounded sequence layouts, since it seems like the API has some 
>> aspects which makes it difficult to deal with them:
>>
>> * it is not possible to establish whether a layout has a size, and 
>> hence whether e.g. passing it to MemorySegment::allocateNative will 
>> blow up
>> * there's no way, given a layout which contains one or more unbound 
>> sequences to replace them with bounded ones - w/o recreating 
>> everything from scratch
>>
>> This patch fixes these problems by:
>>
>> * adding an hasSize() predicate to all layouts
>> * adding a way to 'map' a layout given a path - that is, create a new 
>> layout where one nested element has been replaced using a given unary 
>> operator
>>
>> Separately, I've also added a way to 'select' a nested layout given a 
>> path (which is not strictly necessary, but seems a nice to have).
>>
>> Webrev:
>>
>> http://cr.openjdk.java.net/~mcimadamore/panama/8236267/
>>
>> I've also updated javadoc here:
>>
>> http://cr.openjdk.java.net/~mcimadamore/panama/memaccess_javadoc/jdk/incubator/foreign/package-summary.html 
>>
>>
>> I've done a significant cleanup of the javadoc associated with the 
>> methods accepting layout paths (as well as their implementations), as 
>> there were a number of issues:
>>
>> * the javadoc were not documenting that some path element selection 
>> could fail (e.g. if traversing a layout with no size)
>> * related, the newly created methods should be robust to the lack of 
>> size in a traversed layout (as they are more about selection than 
>> about precise offset computation)
>> * we were not clear (both in spec and impl) re. which PahElement are 
>> allowed on each of the path-accepting methods. For instance, passing 
>> PathElement.sequenceElement() to MemoryLayout::offset() makes no 
>> sense, as it does not select a single layout element with given 
>> offset. Similarly, the newly added methods have other restrictions 
>> which are documented (and tested)
>> * I've added more examples in the MemoryLayout toplevel javadoc, to 
>> show how layout paths can be used
>>
>> Cheers
>> Maurizio
>>
>>
>>