RFR: 8365919: Replace currentTimeMillis with nanoTime in Stresser.java [v3]

[Paul Hohensee]

On Mon, 25 Aug 2025 14:09:13 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 incrementally with one additional commit since the last revision:
> 
>   review

Marked as reviewed by phh (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26879#pullrequestreview-3152368046