[foreign-memaccess+abi] RFR: 8293400: Modify static constructors in MemorySegment [v2]

[Maurizio Cimadamore]

On Tue, 13 Sep 2022 11:45:31 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Simplify creatons of MemorySegments in tests
>
> src/java.base/share/classes/java/lang/foreign/MemorySegment.java line 957:
> 
>> 955:      * The memory segment is automatically freed some unspecified time after it is no longer referenced.
>> 956:      * If a memory segment needs to be deterministically freed, use an appropriate memory session from which
>> 957:      * {@linkplain MemorySession#allocate(MemoryLayout) allocation} can be made instead.
> 
> Suggestion:
> 
>      * The returned memory segment is associated with an {@linkplain MemorySession#openImplicit implicit} memory session. As such, the native memory region associated with the returned segment is freed <em>automatically</em>, some unspecified time after it is no longer referenced. Native segments featuring deterministic deallocation can be obtained using the {MemorySession#allocate} method.

Also, add a `@see` for `MemorySession::allocate` (and probably also one in `MemorySession::allocate` to here)

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PR: https://git.openjdk.org/panama-foreign/pull/718