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

[David Holmes]

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.

If the problem is as suspected then the change to execute the test at a safepoint seems reasonable. Kim had doubts that any other thread should be running in a TEST case (versus TEST_VM case).
The changes to the seed initialization seem unnecessary (in relation to the bug fix) but also harmless. Like all our VM initialization it is safe to do init_random() during VM initialization, so there should not have been any issue in that regard. But as all platforms set the same seed anyway, this is simpler.
Thanks,
David

test/hotspot/gtest/logging/test_logOutputList.cpp line 69:

> 67:   LogLevelType expected_level_for_output[TestOutputCount];
> 68: 
> 69:   os::init_random(0x4711);

I assume this was done to try and get some measure of reproducibility, and now we have lost that, even though it wasn't guaranteed anyway.

test/hotspot/gtest/runtime/test_os.cpp line 119:

> 117: }
> 118: 
> 119: class VM_TestRandom : public VM_GTestExecuteAtSafepoint {

It took me a while to convince myself that none of the existing uses of os::random() can occur concurrently with a safepoint, but that does seem to be the case.

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Marked as reviewed by dholmes (Reviewer).

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