HttpClient creates Quic threads even if HTTP/3 is not in use

[wfurt]

1. Create simple console app with HTTP and run simple http1.1 request on Windows 11 or Server 22.
2. look at application threads.

Application crates 2x threads per core even if HTTP/3 and Quic are not in used. This was originally reported on legacy system with 54 cores. That will create 100+ threads ... for nothing.

We should figure out how to make Quic.IsSupported cheap and defer thread creation until needed.
This will impact legacy app that has no clue tor intention to use Quic or HTTP/3.

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Issue Details

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1. Create simple console app with HTTP and run simple http1.1 request on Windows 11 or Server 22.
2. look at application threads.

Application crates 2x threads per core even if HTTP/3 and Quic are not in used. This was originally reported on legacy system with 54 cores. That will create 100+ threads ... for nothing.

We should figure out how to make Quic.IsSupported cheap and defer thread creation until needed.
This will impact legacy app that has no clue tor intention to use Quic or HTTP/3.

Author:	wfurt
Assignees:	-
Labels:	tenet-compatibility, area-System.Net.Quic
Milestone:	-

[rzikm]

I think we can simply try opening and closing the API registration (that should deallocate the internal MsQuic threadpool), and then lazily reopen it when we actually intend to use it.

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

1. Create simple console app with HTTP and run simple http1.1 request on Windows 11 or Server 22.
2. look at application threads.

Application crates 2x threads per core even if HTTP/3 and Quic are not in used. This was originally reported on legacy system with 54 cores. That will create 100+ threads ... for nothing.

We should figure out how to make Quic.IsSupported cheap and defer thread creation until needed.
This will impact legacy app that has no clue tor intention to use Quic or HTTP/3.

Author:	wfurt
Assignees:	-
Labels:	area-System.Net.Http, tenet-compatibility, area-System.Net.Quic
Milestone:	7.0.0

[karelz]

Triage: This contributes to 1MB per core Working set regression on Windows 2022/Win11+ and on Linux when msquic is present.
We should fix it in 7.0.