Fix Async Cancel

[Wraith2]

fixes #44

This removes two contending locks and adds an interlocked state int similar to the way that timeouts were recently changed. This prevents waiting and allows cancel to proceed only if end of execution hasn't started otherwise cancel is ignored.

There was already an async cancel test which was passing so I added a new one based on the repro from the original thread.

[johnnypham]

Looks good to me. Can you bring the changes to netfx too?

[Wraith2]

Netfx added.

[cheenamalhotra]

The failing TVP Test is an actual error and needs further investigation.
Shouldn't be treated as random failure as it's failing in all test pipelines.

[Wraith2]

Great, just one tiny test to debug...

[Wraith2]

I've put some time into working through TvpMain but I can't work out what the tests are supposed to be doing so I can't isolate what I might have got wrong. Any chance of some help on this?

[DavoudEshtehari]

The TVP failure occurs on StreamInputParam.ImmediateCancelBin().

[Wraith2]

I think I'm going to give up on this. Tests that work locally don't work in the CI, things that work in CI don't work locally and the bizarre threading nature of cancellation makes trying to track down and juggle the exact steps to get all the errors matching up is baroque and frustrating. I'll leave it to the professionals.

[cheenamalhotra]

Hi @Wraith2

We'll help you with that, I'm reopening PR so we can help investigate test issues, don't worry!

[DavoudEshtehari]

Hi @Wraith2, After checking the test failures I noticed TdsParserStateObject.Cancel doesn't get into the if-block that will be fixed by applying the recent changes on netfx (be careful about the confusing CompareExchange because the current values of the current and new parameters should be swapped 😉).