RFR: 8212107: VMThread issues and cleanup [v6]

[Daniel D.Daugherty]

On Fri, 25 Sep 2020 18:27:57 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hmmm.... The old SafepointALot was intended to safepoint as frequently
>> as possible to stress the system. Now we do very little at safepoints so
>> maybe it is time for SafepointALot to evolve. Can you make it so that a
>> SafepointALot happens some fraction of GuaranteedSafepointInterval, e.g.,
>> (GuaranteedSafepointInterval / 4) so four times as often?
>
> All test using SafepointALot the already set the GuaranteedSafepointInterval to a low value in range of ~1-300ms.
> (except for vm boolean flag test which uses SafepointALot  to test a boolean flag)
> For example jni/FastGetField sets GuaranteedSafepointInterval to 1.
> 
> The only case it would really differ is when adhoc adding SafepointALot without GuaranteedSafepointInterval.

If GuaranteedSafepointInterval is set to a lower value than the default on the command line, then I'm okay if
SafepointALot does not do anything extra. However, if GuaranteedSafepointInterval is either the default value or is set
to a higher value, then I would like SafepointALot to cause a safepoint more frequently than the
GuaranteedSafepointInterval. Every GuaranteedSafepointInterval/4 would be a fine definition of "a lot".

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PR: https://git.openjdk.java.net/jdk/pull/228