Reuse cancellation token sources in the Kestrel

[davidfowl]

Today we use the request aborted token when writing large responses in various places. We can reuse these tokens across requests if they haven't been cancelled. We can take advantage of dotnet/runtime#48492 when it becomes available.

Here's what a simple application that uses the request aborted token looks like:

var host = new HostBuilder().ConfigureWebHostDefaults(host =>
{
    host.Configure(app =>
    {
        Task Hello(HttpContext context)
        {
            return context.Response.WriteAsync("Hello World", context.RequestAborted);
        }

        app.UseRouting();

        app.UseEndpoints(routes =>
        {
            routes.MapGet("/", Hello);
        });
    });
}).Build();


await host.RunAsync();

Here's the allocation profile after ~10K requests

Type	Allocations	Bytes	Average Size (Bytes)
- System.Threading.CancellationTokenSource	10,250	656,000	64
- System.SByte[]	1,500	312,000	208
- Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.Http1Connection<Context>	125	97,000	776
- System.IO.Pipelines.Pipe	250	96,000	384
- Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.Internal.SocketAwaitableEventArgs	250	88,000	352
- Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpRequestHeaders	125	67,000	536
- Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpResponseHeaders	125	49,000	392
- System.IO.Pipelines.BufferSegmentStack.SegmentAsValueType[]	250	38,000	152
- System.String	504	35,570	70.58
- Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.Internal.SocketConnection	125	31,000	248
- System.Object	1,125	27,000	24

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[kshyju]

@davidfowl

I am going through the PRs in Continuous Improvement project as an optimization learning exercise.

Here's the allocation profile after ~10K requests

Could you please share what tooling was used to generate the above data ? Thank You!

[davidfowl]

Could you please share what tooling was used to generate the above data ? Thank You!

Visual Studio 2019's new allocation profiler https://docs.microsoft.com/en-us/visualstudio/profiling/dotnet-alloc-tool?view=vs-2019. You can copy as markdown 😄