RunThreadLocalTest8_Values failed in CI

[stephentoub]

http://dotnet-ci.cloudapp.net/job/dotnet_corefx_windows_release_prtest/4721/console

System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values [FAIL]
        RunThreadLocalTest8_Values: Expected values to contain both previous values and 1000 new values
        Expected: True
        Actual:   False
        Stack Trace:
           d:\j\workspace\dotnet_corefx_windows_release_prtest\src\System.Threading\tests\ThreadLocalTests.cs(259,0): at System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values()

[stephentoub]

Failed again here:
http://dotnet-ci.cloudapp.net/job/dotnet_corefx_windows_debug_prtest/6046/console

System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values [FAIL]
        RunThreadLocalTest8_Values: Expected values to contain both previous values and 1000 new values
        Expected: True
        Actual:   False
        Stack Trace:
           d:\j\workspace\dotnet_corefx_windows_debug_prtest\src\System.Threading\tests\ThreadLocalTests.cs(258,0): at 

[kouvel]

I don't see anything wrong with this test, and it's passing consistently on my machine. I don't see anything wrong with the implementation either. It looks like the test is still enabled, and the noted failures were from a while back. Is there a way to check if this test has failed recently?

[stephentoub]

It's only failed very intermittently, but as you say it doesn't look like a test issue. My guess is that there's a real bug somewhere that's triggered by a very rare race condition.

[kouvel]

Yea, I looked at the implementation as well and couldn't find any issues. ThreadLocal.GetValuesAsList() is accessing the LinkedSlot linked list (which is global) without a lock. It might miss concurrently added slots since new slots are added to the beginning, which is probably ok. In the way this test is using the ThreadLocal instance, there are no concurrency issues at the time of calling GetValuesAsList().

I can try to add the actual count and any missing values to the error message, to see if that helps. We can see if it's just empty or missing a few items.

[stephentoub]

This just failed again:
http://dotnet-ci.cloudapp.net/job/dotnet_corefx/job/outerloop_win10_debug/128/consoleFull

12:32:00      System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values [FAIL]
12:32:00         RunThreadLocalTest8_Values: Expected values to contain both previous values and 1000 new values. Actual count: 1001. Missing items: 1001
12:32:00         Expected: True
12:32:00         Actual:   False
12:32:00         Stack Trace:
12:32:00            d:\j\workspace\outerloop_win---0cba2915\src\System.Threading\tests\ThreadLocalTests.cs(276,0): at System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values()

[bartdesmet]

Another occurrence @ https://ci.dot.net/job/dotnet_corefx/job/master/job/windows_nt_debug_prtest/775/

17:36:24      System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values [FAIL]
17:36:24         RunThreadLocalTest8_Values: Expected values to contain both previous values and 1000 new values. Actual count: 1001. Missing items: 1001
17:36:24         Expected: True
17:36:24         Actual:   False
17:36:24         Stack Trace:
17:36:24            D:\j\workspace\windows_nt_de---4526f5ff\src\System.Threading\tests\ThreadLocalTests.cs(276,0): at System.Threading.Tests.ThreadLocalTests.RunThreadLocalTest8_Values()