Integrated: 8275063: Implementation of Foreign Function & Memory API (Second incubator)

[Maurizio Cimadamore]

On 24/11/2021 21:12, Ty Young wrote:
> Regardless of what's exposed, how is someone supposed to use a 
> VarHandles when the layout that you use to create a MemorySegment has 
> a mutable meaning? Using a long handle on a MemorySegment created 
> using the ValueLayout of an int just causes an index out of bounds 
> exception, for example. 

Not sure I follow here - what do you mean by "mutable" meaning?

Sure, if you create a segment with a layout that is 4 bytes and you try 
to get 8 bytes out of it there's gonna be an issue.

But I don't understand what you mean by mutable. Clearly you can't mean 
mutable as in "this thing can go from 4 byte of size to 8 byte". So you 
probably refer to the fact that a native long on windows is 4 bytes, 
where on other 64-bit platforms is 8 bytes? That would be true of course 
(but now we're not speaking about JAVA_XYZ layouts anymore, are we?).

To deal with C types in the correct way, jextract emits layouts for all 
the basic primitive types and typedefs. So, since you're not using 
jextract you would have to do something similar; or even used sized 
constant as you mentioned, if you want to achieve more portability.

Maurizio