Hanging tests on single threaded Ubuntu environment

[JunTaoLuo]

It seems like some tests in EF are hanging consistently on agent projectk-tc-ag6, see http://aspnetci/viewLog.html?buildId=90832&buildTypeId=XPlat_Linux_UbuntuUniverseCoreCLR&tab=buildLog#_focus=115519. I took a brief look at the test set up in https://github.com/aspnet/EntityFramework/blob/f732e3c7c1a680a944b9aafaf34bef88ed8a19c4/test/Microsoft.EntityFrameworkCore.FunctionalTests/DatabaseErrorLogStateTest.cs and it seems very similar to the problem I ran into in aspnet/Hosting#523. Probably needs some investigation.

[divega]

One of the tests that is failing is DatabaseErrorLogStateTest.Query_logs_DatabaseErrorLogState_during_LINQ_enumeration_async which is a sync test that is testing an async query method with a Wait() at the end (so it is not very surprising that it hangs when running single threaded).

There are many more tests in the same class that use the same pattern. I am not sure there is a reason we haven't made the tests async. @anpete?

[anpete]

cc @rowanmiller who wrote this originally.

[anpete]

@divega I think the reason here is to DRY-up the result verification. Suggest we split async into different tests like we do usually. NB. I have seen this pattern in some of our other tests, too.

[divega]

Talked to @smitpatel trying to figure out what the resolution was for this issue. We actually haven't changed these sync tests that invoke async APIs with .Wait() to be async, but these particular tests haven't hanged or deadlocked recently, hence "no repro". cc @anpete, @ajcvickers

[ajcvickers]

@divega I would actually like to open this for backlog/cleanup. It's easy to write tests that can be run twice, once sync, once not, without using Wait. It would be good to cleanup all our tests to do that (where we need to test both sync/async). Let's discuss if you feel strongly it should remain closed.

[divega]

@ajcvickers sounds great.

[divega]

@smitpatel do you think we should do this clean up task now?

[smitpatel]

Yes we should. It would be easy. And I suspect some day xUnit will start acting up seeing Wait()

[smitpatel]

Note for implementer: Look at SqlServerDatabaseCreatorExistsTest which utilizes common method for sync/async both testing without using Wait()