RFR: 8364638: Refactor and make accumulated GC CPU time code generic [v5]

[Jonas Norlinder]

On Thu, 14 Aug 2025 12:19:58 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Looked closer at the users of this and one user is `ThreadMXBean.getThreadCpuTime(long id)`. Looking at the API docs for that, returning -1 is not a error but the expected result for a terminated thread. So I think we should remove these warnings.
>
>> ... it might happen from time to time without it being a very big deal?
> 
> My concern is that we get a number on cpu-time without knowing the number is off by a large margin when failure occurs, so there should probably be some warning/msg somewhere.

I don't sample GC threads that have terminated, so I would prefer not having the warning as well, as it would not fail unless the machine is in a bad state and then we would have larger issues at hand anyways?

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PR Review Comment: https://git.openjdk.org/jdk/pull/26621#discussion_r2276583734