cleanup action captures original segment

[Wojciech Lukowicz]

Hi,

I wanted to verify some automatic arena gets cleaned up and wrote
something equivalent to:

var arena = Arena.ofAuto();
arena.allocate(0).reinterpret(arena, _ -> System.out.println("cleanup"));
arena = null;

However, after many GC cycles, the cleanup action never got executed.

Turns out AbstractMemorySegmentImpl#reinterpretInternal creates a lambda
wrapper around the cleanup action which captures the original segment
and consequently its scope, doing here what the JavaDoc warns against:

> Furthermore, if the provided scope is the scope of an automatic arena,
> the cleanup action must not prevent the scope from becoming unreachable.
> A failure to do so will permanently prevent the regions of memory
> allocated by the automatic arena from being deallocated.

Not an issue in the typical case of reinterpreting global segments, but
the behavior seems accidental.

Thanks,
Wojciech