RFR: 8268906: gc/g1/mixedgc/TestOldGenCollectionUsage.java assumes that GCs take 1ms minimum
kbarrett at openjdk.java.net
Fri Jun 18 18:03:30 UTC 2021
On Fri, 18 Jun 2021 17:43:05 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:
> can I have reviews for this change to a test that incorrectly assumed that GCs take 1ms minimum?
> At the end of the test, MXBeans' `getCollectionTime()` is compared against one taken two gcs earlier. If these two gcs are very short, `getCollectionTime()` returns the same value as before because its resolution is 1ms.
> The `getCollectionTime()` documentation states:
>> Returns the approximate accumulated collection elapsed time in milliseconds. This method returns -1 if the collection elapsed time is undefined for this collector.
>> The Java virtual machine implementation may use a high resolution timer to measure the elapsed time. **This method may return the same value even if the collection count has been incremented if the collection elapsed time is very short.**
> Which is what the test tested
> Testing: test does not fail any more after some VM hack so that `getCollectionTime()` returns very low values.
Marked as reviewed by kbarrett (Reviewer).
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