[HttpListener] HttpListener tests are blocking xunit workers, causing hangs

[stephentoub]

Lots of the tests that are async are doing synchronous work that's dependent on something else happening, resulting in deadlocks/hangs when xunit parallel execution is enabled, in particular on older OSes where things run slower / more stuff completes asynchronously. Examples include synchronous sends/receives, spinning until a socket closes, doing .Wait() to block waiting for an async method, etc.

[danmoseley]

Hang. https://ci.dot.net/job/dotnet_corefx/job/master/job/ubuntu14.04_debug_prtest/8241/consoleFull#-18258434524b7730ef-150b-4be7-a00f-82ba6c50792b

[stephentoub]

This issue was not meant to represent arbitrary hangs in the tests, but rather a specific case of them that was addressed by dotnet/corefx#20104 by disabling parallelism, and we can live without the parallelism in the 2.0 timeframe. That's why I put it in future. Any current hangs would be due to something else, actually a faulty test or product rather than a poor interaction between the tests and xunit's infrastructure, and there are other issues for that, e.g. https://github.com/dotnet/corefx/issues/20246. Moving back to future.

[CIPop]

/cc @Caesar1995 @davidsh @DavidGoll

[karelz]

Triage: Next steps: Revert the change, run it locally and debug the hangs.

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