Transport.Sockets.IOQueue -> IThreadPoolWorkItem

[benaadams]

Resolves #4357

In combination with dotnet/coreclr#21159 this is the final piece to bring the steady state allocations for Plaintext Platform to 0 bytes/s (for 7M+ request/s) in .NET Core 3.0

Which fits with the goals of aspnet applications being able to run under lower memory conditions (See: "Proposal for .NET Core GC Support for Docker Limits")

/cc @sebastienros @halter73 @pakrym @davidfowl @Tratcher

[pakrym]

LGTM

[halter73]

@sebastienros Can you benchmark this?

[benaadams]

In combination with dotnet/coreclr#21159 this is the final piece to bring the steady state allocations for Plaintext Platform to 0 bytes/s (for 7M+ request/s) in .NET Core 3.0

Which fits with the goals of aspnet applications being able to run under lower memory conditions (See: "Proposal for .NET Core GC Support for Docker Limits")

[davidfowl]

We need to collect a profile on Linux. To make sure we slash the allocations across the board.

[sebastienros]

Benchmarking PlatformPlaintext on Windows with 512 connections

Description	RPS	CPU (%)	Memory (MB)	Avg. Latency (ms)	Startup (ms)	First Request (ms)	Latency (ms)	Ratio
Baseline	3,411,048	80	327	5.3	250	27.7	0.4	1.00
IThreadPoolWorkItem	3,439,712	80	282	5.2	248	30.1	0.5	1.01

[benaadams]

Memory 327 MB -> 282 MB suggests a positive impact 😄

[pakrym]

@benaadams do you mind rebasing this?

[benaadams]

Rebased

[benaadams]

CI errors #6127, #6135 and #6136