RFR: JDK-8220671: Initialization race for non-JavaThread PtrQueues

[Roman Kennke]

>> On Mar 19, 2019, at 6:56 PM, Roman Kennke <rkennke at redhat.com> wrote:
>> My current idea goes roughly like this (includes some Shenandoah mess
>> that will not be there in final webrev):
>>
>> http://cr.openjdk.java.net/~rkennke/JDK-8221102.patch
>>
>> However, this *still* doesn't solve my crashing testcase. Digging even
>> deeper...
>>
>> Roman
> 
> I have a different idea for this new problem.  I’ll post something more tomorrow.
> 
> Let me know what you find with your test case.  Actually, can you describe how to reproduce?

Something like this:
for i in {1..20}; do CONF=fastdebug LANG=C LOG=info make run-test
TEST=gc/shenandoah/TestStringDedupStress.java; done

should make it fail somewhat reliably. The attached patch
baddertest.patch should make it more likely (it launches only
aggressive-mode test runs). Also, it seems more likely when running on a
larger machine (with more cores).

The test started failing somewhere between jdk-13+9 and jdk-13+11, and I
bisected it down to NJT PtrQueues change. It also seemed like the most
likely candidate in that frame. It only ever seems to crash with
+UseStringDuplication, and since the strdedup thread does SATB, it seems
plausible that the change affects this.

Any help would be greatly appreciated.

Thanks,
Roman
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