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

[Roger Riggs]

On Tue, 29 Sep 2020 00:06:02 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

ok, if I read the code closely and know how the promoted build process works then I see your rationale.
Please update the bug report and edit the PR description to describe the conditions under which the seed
for random is computed from the build number. Its might be clearer to refer to the Runtime.Version build information
in the description.  Also make it clear that unless the system property is set, it will use a 'random' seed.

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Changes requested by rriggs (Reviewer).

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