RFR: 8287788: Implement a better allocator for downcalls [v14]

[Matthias Ernst]

On Wed, 22 Jan 2025 20:05:25 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> Matthias Ernst has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   (c)
>
> test/jdk/java/foreign/TestBufferStack.java line 122:
> 
>> 120:                 thread -> Assert.assertTrue(thread.isAlive()));
>> 121:     }
>> 122: }
> 
> I think we should also have a test that exercises the new code in the context of the linker. We have some tests that test downcall -> upcall with by-value structs, but I think we should also have a test that keeps going until it exhausts the buffer. Something like `test/jdk/java/foreign/stackwalk/TestReentrantUpcalls.java` (but without the `Whitebox` stuff).

Done. Verified manually during test that we satisfy the first 5 frames from the stack and fall back afterwards.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1926567636