RFR: 8292407: Improve Weak CAS VarHandle/Unsafe tests resilience under spurious failures [v4]

[Paul Sandoz]

On Fri, 19 Aug 2022 18:14:16 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> We have a few reports that existing Weak* VarHandle tests are still flaky, for example on large AArch64 machines or small RISC-V machines.
>> 
>> The flakiness is intrinsic to the nature of Weak* operations under tests, that can spuriously fail. The last attempt to fix these was [JDK-8155739](https://bugs.openjdk.org/browse/JDK-8155739). We need to strengthen these a bit more.
>> 
>> The actual values depend on the successful testing on known-failing platforms. I ballparked bumping the attempts 5x and introducing the delay would help without exploding test time in worst cases.
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:
> 
>  - Rework timeouts
>  - Merge branch 'master' into JDK-8292407-varhandle-weak-resilient
>  - Merge branch 'master' into JDK-8292407-varhandle-weak-resilient
>  - Update copyrights
>  - Also do Unsafe tests
>  - Fix

It's awkward to manage this across various hardware, esp. if the hardware is less mature (perhaps combined with a less mature HotSpot implementation). The approach looks reasonable, but it would be nice if we could just increase the retries and waiting values on weak LL/SC hardware or at least follow up with something like that later on.

As a quick experiment could we annotate fields with `@Contended` and see if that reduces the number of retries?

-------------

PR: https://git.openjdk.org/jdk/pull/9889