RFR: 8271834: TestStringDeduplicationAgeThreshold intermittent failures on Shenandoah [v3]

[Per Liden]

On Fri, 10 Sep 2021 13:54:34 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> To trigger young GC, the test fills heap with -Xmn amount of garbage. However, -Xmn does not apply to non-generational GC, such as Shenandoah, and -Xmn amount of garbage, sometimes, it not enough to trigger GC, therefore, there is no guarantee that strings can reach deduplication age threshold.
>> 
>> I purpose to use MXBean to get exact gc count to ensure expected gc cycles actually performed.
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Per's comment

Marked as reviewed by pliden (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/5428