RFR: 8365919: Replace currentTimeMillis with nanoTime in Stresser.java [v2]

[Albert Mingkun Yang]

On Fri, 22 Aug 2025 18:37:47 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Mostly a mechanic change from `currentTimeMillis()` to `nanoTime()/1000000`. It also removes `finishTime` to avoid overflowing.
>> 
>> The change in `iteration()` is to ensure `currentTime` is properly initialized.
>> 
>> (Was investigating a timeout on Windows-x64, which led me to this code. I think this fix is good enough by its own.)
>>  
>> Test: tier1-5
>
> Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - review
>  - Merge branch 'master' into test-nano-time
>  - test-nano-time

I have changed to use nanoseconds for all fields, to avoid excessive unit conversion.

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PR Comment: https://git.openjdk.org/jdk/pull/26879#issuecomment-3220455460