RFR: 8253750: use build-stable default seed for Utils.RANDOM_GENERATOR

[Roger Riggs]

On Fri, 2 Oct 2020 15:39:01 GMT, Igor Ignatyev <iignatyev at openjdk.org> wrote:

>> Hi all,
>> 
>> could you please review the patch which updates `jdk.test.lib.Utils` to use md5 hash-sum of `java.vm.version` property
>> as default seed for `Utils.RANDOM_GENERATOR`?
>> from JBS:
>>> using the same seed for all runs of a build will make it possible (easier) to compare results from different test runs
>>> (e.g. on different platforms, w/ different flags) and consequently will make test results analysis easier.
>> 
>> the patch also updates `RandomGeneratorTest` test, so it expects now that the same values are generated if no seed is
>> provided.
>> testing: ✅ tier1
>
> ping?

Is this really a good idea?  The purpose of using random numbers is to get broader coverage on multiple runs.
If the seed only changes once per version (6 months), that reduces test coverage.
At least for dev submitted runs, I would like to be different for every build (unless overridden).

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PR: https://git.openjdk.java.net/jdk/pull/391