[release/5.0-rc2] Fix exception mapping during expect 100 cancellation.

[github-actions]

Backport of #41800 to release/5.0-rc2
Contributes to #40388

/cc @ManickaP

Customer Impact

The related code block has been introduced in 5.0 (in PR #38774) and there is a regression from 3.1: a different type of exception is thrown for cancellation than TaskCancelledException. This could potentially break existing code that works on 3.1.

Testing

Discovered during HTTP stress tests, eg.: Run HttpStress - HTTP 1.1. It's been occurring on every HTTP 1.1 run, after the fix, the error disappeared.

Risk

Low. Also this affects only newly introduced code in 5.0.

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[wfurt]

LGTM

[danmoseley]

Is this likely to have a customer impact? I'm guessing so - throwing something other than TaskCanceledException is highly unexpected?

[danmoseley]

Test failure is #42024

[ManickaP]

Is this likely to have a customer impact? I'm guessing so - throwing something other than TaskCanceledException is highly unexpected?

Yes, that is my concern and a reason I started this port.

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[ManickaP]

All test failures unrelated, see #42024.
@scalablecory could you re-review pls.

[danmoseley]

Is any test imaginable? Outside of stress.

[danmoseley]

Approved in email. It would be good to consider how to test this -- in System.Threading there are quite a few unit tests that successfully protect fixes for bugs that rarely repro using lots of looping and tricks. I do not know whether that is possible here.

That need not hold up merging this though.

[ManickaP]

@danmosemsft This is a timing issue, you need to fire the cancellation at a very precise moment and process everything around it in a certain order. Even if I were to change production code to manually control the timing, it would still be complicated.