Question about global SegmentScope

[刘希晨]

Got it. I read about Java21's new updates about FFI, it's more clear now!
Thanks for answering!

Maurizio Cimadamore <maurizio.cimadamore at oracle.com> 于2023年4月17日周一 22:38写道：

>
> On 17/04/2023 15:23, 刘希晨 wrote:
> > Thank you for the clarification. I am stuck with my mind because I
> > thought that if the SegmentScope() is global, then even if the
> > MemorySegment Object has been GCed, the underlying memory won't be
> > released, not until the JVM exit. (Is that correct? I think that's the
> > difference between the global scope and the auto scope).
>
> This is not correct.
>
> The segment you get back from a native library has an "unknown scope"
> (as said, in the Java 21, this is different from the "global" scope,
> which is guaranteed to be always alive until VM termination). Segments
> with "unknown" scopes can be accessed, but at your own risk, as the
> region of memory backing the segment could be freed (in the general
> case) at any time by the native library.
>
> Now, in reality things are not as bleak as they sound - while _in
> principle_ the region backing the segment might disappear w/o notice, in
> practice a well-defined library will advertise who and when should
> release the regioin of memory associated with a pointer that has been
> returned by some function. But this is a detail that is typical buried
> in the documentation of the function you are interacting with - it
> cannot be expressed in the static type system of the C language and the
> FFM API has no knowledge of it.
>
> Maurizio
>
>
>
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