[foreign-memaccess] RFR 8224483: Split MemoryAddress into separate address/region abstractions

[Jorn Vernee]

Hi,

Some comments:

MemoryAddress.java
- I'm wondering if it makes sense to move the ofByteBuffer method to 
MemorySegment? (This would also mirror the internal impl)

MemoryAddressImpl.java
- `((MemoryScopeImpl) segment().scope()).checkAlive()` is used in a 
couple of places. Maybe move this to MemorySegmentImpl, and then call 
segment.checkAlive()?
- I think asDirectByteBuffer needs to do a liveness check as well 
(should probably just call checkAccess?).

MemorySegmentImpl.java
- OfEverything is unused and could be removed at this point.
- `resize` needs to check for negative offset as well, since we're 
coming directly from user code. I think this check could be replaced 
with a call to checkRange (adding a < 0 check for the length there).

Cheers,
Jorn

Maurizio Cimadamore schreef op 2019-05-21 13:52:
> Following discussion at [1], I decided to go ahead and split
> MemoryAddres into two abstractions:
> 
> * MemroyAddress will now embody an offest into a...
> * MemorySegment, which represent a contiguous region of memory
> 
> The name MemorySegment came from an internal discussion with Brian,
> where he pointed out that MemoryScope and MemoryRegion where a bit too
> overlapping, in the english sense of the word. MemorySegment suggests
> something that has lower/upper boundaries.
> 
> Webrev:
> 
> http://cr.openjdk.java.net/~mcimadamore/panama/8224483/
> 
> There are many changes since the last patch discussed - mostly
> because, as I was adding the lower-level allocate methods in
> MemoryScope I realized that we were missing a lot of checks (w.r.t.
> alignment and sizes). I've added those and added tests for these as
> well (2 new tests have been added). Also, the Scope::allocate API
> should reflect the fact that Unsafe might fail to allocate - again
> added a test for this.
> 
> Maurizio