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

[Coleen Phillimore]

On Wed, 25 Nov 2020 01:00:57 GMT, David Holmes <dholmes 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.
>
> 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.

Yes, I don't know why this was done here.

> 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.

In this test I'm assuming that once this thread gets to a safepoint, it should be the only thing running. Unless maybe some concurrent GC threads.  I don't know what they would be doing for this test case though.

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