RFR: 8359827: Test runtime/Thread/ThreadCountLimit.java should run exclusively [v8]

[SendaoYan]

On Wed, 23 Jul 2025 02:39:44 GMT, SendaoYan <syan at openjdk.org> wrote:

>> Hi all,
>> 
>> The test runtime/Thread/ThreadCountLimit.java was observed fails when run with other tests. The test start subprocess with [shell prefix command](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/runtime/Thread/ThreadCountLimit.java#L82) `ulimit -u 4096` which intend to limite the usage of thread number. But this will cause test fails when this test run with other tests. I create a demo to demonstrate that.
>> 
>> I start a java process which will create 5k threads, and then I can not start new java process with prefix `ulimit -u 4096` on the same machine.
>> 
>> <img width="1573" height="182" alt="image" src="https://github.com/user-attachments/assets/8dd53ade-cad7-4a2f-b5d9-d4b2d200b728" />
>> 
>> 
>> [ManyThreads.java.txt](https://github.com/user-attachments/files/21324354/ManyThreads.java.txt)
>> 
>> So it's necessary to make this test run sperately to make this test success.
>> Change has been verified locally, test-fix only, risk is low.
>
> SendaoYan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert change to TEST.groups

Testing in our CI was fine - test passes on third iteration with 12288 in all case.

[ThreadCountLimit_id0.jtr.txt](https://github.com/user-attachments/files/21386820/ThreadCountLimit_id0.jtr.txt)

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PR Comment: https://git.openjdk.org/jdk/pull/26401#issuecomment-3107333362