[foreign-memaccess+abi] RFR: 8296417: Make memory session a pure lifetime abstraction [v3]

[Jorn Vernee]

On Fri, 4 Nov 2022 22:25:05 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> test/jdk/java/foreign/TestSegmentAllocators.java line 90:
>> 
>>> 88:                     } catch (IndexOutOfBoundsException | IllegalStateException ex) {
>>> 89:                         //failure is expected if bound
>>> 90:                         assertTrue(isBound);
>> 
>> Not sure I get this `catch`. AFAICS only a slicing allocator is bound, which should result in `NULL` being returned, not an exception, right?
>
> You are correct in the sense that slicing allocator returns NULL when it cannot allocate. However, if we allocate using e.g. `SegmentAllocator.allocate(ValueLayout.OfInt, int)` there will be issues because the returned segment has zero size and we will be trying to set a value on it. I think returning NULL here is perhaps too clever, we should just throw IOOBE on the allocate method - agree?

Ah, I see. But, returning `NULL` seems nice for composing with other allocators. I guess you'd need to override all the methods of SegmentAllocator in SlicingAllocator to forward the `NULL` returned by the base `allocate`.

If you go for throwing an exception, I suggest sticking with OOME though.

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PR: https://git.openjdk.org/panama-foreign/pull/750