RFR: 8254042: gtest/GTestWrapper.java failed os.test_random

[Thomas Stuefe]

On Tue, 24 Nov 2020 23:38:52 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> The function os::init_random() and os::random() both set the _rand_seed. This test thinks nothing can change the seed while it is computing its expected value.
> I changed the test to run in a VM operation safepoint.  Alternately, I can change the test to not verify the random value computed in the loop, or remove the test.
> Ran tier1 tests on linux-x64 and windows-x64.

Hi Coleen,

Why is someone concurrently changing the seed? I thought "TEST" tests do not start the VM? Or is it that some earlier test already did?

Could we not just change the test to use os::next_random(seed)? 
That would be a two-line change: remove the init_random call, and replace os::random() with `num = seed = os::next_random(seed);`

That said, moving the initialization out of the platform files and initialize the seed directly makes sense.

If you want to stay with your approach of making os::init_random() only available at safepoint, could you make it private? CDS could - or arguably should - use the same technique as outlined above, using os::next_random with an own seed instead of os::random.

A third possibility would be to keep the seed THREAD_LOCAL. 

Cheers, Thomas

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PR: https://git.openjdk.java.net/jdk/pull/1422