[foreign] RFR : Move array-like methods from Pointer to Array

[Jorn Vernee]

Update webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/arrays/webrev.04/

Added 2 `iterate` methods to Pointer, one that takes a predicate, and 
one that takes a pointer. Should I also add tests for these? (elements() 
was not being tested previously it seems).

Thanks,
Jorn

Maurizio Cimadamore schreef op 2018-11-19 16:27:
> <snip>
>>> 
>>> Stream<Pointer<T>> elements(Predicate<? super Predicate<T>> hasNext)
>> 
>> Yes, this is a nice idea. Maybe we'd also want to have an overload 
>> that just takes a `Pointer<T>` as an argument, and iterations will be 
>> up until that pointer.
> Sure, the pointer-end overload sounds like a nice idea!
>> 
>>> And this would generally applicable to both arrays and pointers. No
>>> guesswork involved, users iterating on pointers will have to provide
>>> an explicit termination condition; if they get it wrong, they will 
>>> get
>>> some exception when dereferencing the wrong memory location.
>> 
>> Well, for native-allocated pointers this will invoke undefined 
>> behavior or possibly crash the VM (or enable access to VM internals? 
>> I'm not sure what security is in place there currently).
> 
> A possibility there would be to avoid using EVERYTHING as a backing
> region. That is, the binder could, in principle, generate regions that
> are small enough only to contain the region that we actually want to
> access (e.g. starts at base address , ends at base address + pointee
> layout size). If the client is not happy with that and knows that the
> pointer is a pointer to some kind of a buffer, perhaps an (unsafe?)
> operation could be provided to relax the memory region boundaries
> beneath the pointer.
> 
> But overall I think we should strive for the 'no VM crashes if you are
> only using the safe API' (although we don't have to get there in one
> step).
> 
> <snip>
> 
>> 
>> 
>>> As a final point, I think we should implement elements() using
>>> Stream.iterate (and possibly document it in the API).
>> 
>> Agreed. Maybe we should also rename Pointer::elements to 
>> Pointer::iterate ?
> 
> I like that.
> 
> Cheers
> Maurizio
> 
>> 
>> Jorn