RFR: 8349146: [REDO] Implement a better allocator for downcalls [v8]

[Maurizio Cimadamore]

On Fri, 2 May 2025 11:36:56 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Cleanup and only create CleanupAction once per thread
>
> src/java.base/share/classes/jdk/internal/foreign/BufferStack.java line 127:
> 
>> 125:                     arena,
>> 126:                     new SlicingAllocator(arena.allocate(byteSize, byteAlignment)),
>> 127:                     new CleanupAction(arena));
> 
> any reason why you didn't use a lambda here?

Also, not a big fan of records here -- it seems that many implementation details such as cleanup action, lock and slicing allocator are "leaked out" to the caller, that is now responsible to set things up correctly. I think a `PerThread` class with a constructor taking arena, size, alignment would make the code less coupled and more readable.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24829#discussion_r2071496742