Use the PoolingAsyncValueTaskMethodBuilder to remove state machine allocations for async reads

[davidfowl]

Use [AsyncMethodBuilder(typeof(PoolingAsyncValueTaskMethodBuilder<>))] on Kestrel ReadAsync methods to remove per read allocations in the mainline body reading logic.

Places of interest:

• aspnetcore/src/Shared/ServerInfrastructure/DuplexPipeStream.cs

  Line 115 in d1c349f

  private async ValueTask<int> ReadAsyncInternal(Memory<byte> destination, CancellationToken cancellationToken)

• aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http/Http1UpgradeMessageBody.cs

  Line 95 in d1c349f

  private async ValueTask<ReadResult> ReadAsyncInternalAwaited(ValueTask<ReadResult> readTask, CancellationToken cancellationToken = default)

• aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http2/Http2MessageBody.cs

  Line 92 in d1c349f

  public override async ValueTask<ReadResult> ReadAsync(CancellationToken cancellationToken = default)

• aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http/Http1ContentLengthMessageBody.cs

  Line 32 in d1c349f

  public override async ValueTask<ReadResult> ReadAsyncInternal(CancellationToken cancellationToken = default)

• aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http3/Http3MessageBody.cs

  Line 71 in d1c349f

  public override async ValueTask<ReadResult> ReadAsync(CancellationToken cancellationToken = default)

cc @BrennanConroy Part of this is to make WebSockets allocation free.

[BrennanConroy]

Is that feature described anywhere? Would love to read about it.

[davidfowl]

dotnet/runtime#49903

[davidfowl]

cc @stephentoub

We should be able to run an end to end websocket test to verify 0 allocs with a private of this change.

[davidfowl]

Also cc @benaadams

[stephentoub]

We should be able to run an end to end websocket test to verify 0 allocs with a private of this change.

It won't be zero. It should be very significantly reduced. The goal of the pooling isn't to avoid every allocation, but to reduce it while also not introducing bottlenecks or leaks.