[foreign-memaccess+abi] RFR: 8270376: Finalize API for memory copy [v9]

[leerho]

Yes, now I remember. Thank you.  I apologize for the redundant request.
Nonetheless, I guess I am having difficulty in figuring out how to use this
allocator in our use case.  Let me try an elementary example.

public class Parent {
>
>   MemoryScope scope = defineScope(...);
>   MemorySegment arena = defineArenaSegment(..., scope);
>   MemorySegment[] segArr = //allocate a large number of segments as slices
> of arena
>
>   Aggregator[] aggArr = //array of aggregators that operate each in their
> own segment
>   for (int i=0; i < segArr.length(); i++) {
>     aggArr[i] = new Aggregator(segArr[i]);
>   }
>
>   //Start the process of updating all the aggregators with data. The
> parent has no clue as to

  // which aggregators will need more memory.


>   public class ParentAllocator extends SegmentAllocator {
>     @Override
>     public MemorySegment allocate(long bytesSize, long bytesAlignment) {
>       ...
>     }
>   }
> }


> public class Aggregator {


>   public Aggregator(MemorySegment seg) {}


>   public void update(data) {
>     //oops, my segment is full.  I need a larger segment.
>     //How do I access ParentAllocator? Unless I pass it along with the
> segment?
>   }


}

On Wed, Aug 11, 2021 at 2:44 PM Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> I've resurrected an older conversation here:
>
> https://mail.openjdk.java.net/pipermail/panama-dev/2021-April/013191.html
>
> At that time we discussed using a custom allocator to track allocation
> pressure. I think that's still the way to go.
>
> Adding more features on ResourceScope is IMHO not the way to go, given
> that a ResourceScope is not used just for memory segments. If you want
> to keep track of how much memory is allocated, likely you need a custom
> allocator which has the ability to do that, and react accordingly, which
> is why the SegmentAllocator is there. Note that a SegmentAllocator can
> be built on top of a scope, e.g. you don't have to give up scopes (see
> what we do for arena allocators): e.g. you start with a scope, wrap it
> into an allocator and then use the allocator.
>
> Maurizio
>
> On 11/08/2021 22:29, Maurizio Cimadamore wrote:
> > I have to admit, I have trouble understanding what you are proposing -
> > e.g. what this callback would be for. What calls to resource scope do
> > you wish to intercept?
>