RFR: 8340307: Add explanation around MemorySegment:reinterpret regarding arenas

[Maurizio Cimadamore]

On Wed, 30 Oct 2024 12:42:16 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> I think it's technically correct, but I think it's starting off on the wrong foot. There's no transfer of ownership happening, `reinterpret` just returns a view of the old memory region with a new scope borrowed from the given arena. I think there is a conceptual difference between a segment allocated by a given arena, and one reinterpreted with a given arena, even if they act very similar. I think calling that concept by another name will help people's understanding.

I'm not too sure such a different exist. As a client of the segments there's literally no way to tell them apart. I still feel there's two concerns here - e.g. (a) how do I use a reinterpreted segment and, (b) as the creator of the reinterpreted segment, what should I look out for. The answer to (a) is, really, "like any other segment allocated by the provided arena".

Perhaps we can clarify by saying:

"In other words, this method returns a segment that can be used as any other segment allocated using the provided arena."

But then, somewhere else say:

"The returned segment is backed by the same memory region as that of the original segment. As such, the region of memory backing the returned segment is truly deallocated only when the original segment's arena is closed."

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PR Review Comment: https://git.openjdk.org/jdk/pull/21761#discussion_r1822572067