IFeatureCollection has been disposed when trying to access HttpContext.Request.Headers

[Jasdo]

Steps to reprodce

1. Create a simple API ASP.NET Core 3.1 Web Application using Visual Studio 2019 template.
2. In the handler method, add access to HttpContext.Request.Headers.
3. Create a REST client that sends many requests simultaneously.

The result is that eventually, a System.ObjectDisposedException will be thrown upon accessing HttpContext.Request.Headers.

Startup code

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<WeatherForecastController>();
        services.AddMvc().AddControllersAsServices();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseHttpsRedirection();
        app.UseRouting();
        app.UseAuthorization();
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

Controller code

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
    };

    private readonly ILogger<WeatherForecastController> _logger;
    public WeatherForecastController(ILogger<WeatherForecastController> logger)
    {
        _logger = logger;
    }

    [HttpGet]
    public IEnumerable<WeatherForecast> Get()
    {
        var headers = HttpContext.Request.Headers;
        var rng = new Random();
        return Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateTime.Now.AddDays(index),
            TemperatureC = rng.Next(-20, 55),
            Summary = Summaries[rng.Next(Summaries.Length)]
        })
        .ToArray();
    }
}

Client code

static void Main(string[] args)
{
    Parallel.For(0, 3000, i =>
    {
        var getWeatherUri = new Uri("https://localhost:44341/weatherforecast");

        MediaTypeWithQualityHeaderValue requestHeader = new MediaTypeWithQualityHeaderValue("application/json");
        var client = new HttpClient();
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(requestHeader);
        var response = client.GetAsync(getWeatherUri.AbsoluteUri).Result;
        if (!response.IsSuccessStatusCode)
        {
            throw new Exception($"{response.StatusCode}: {response.RequestMessage} | {response.ReasonPhrase}");
        }
    });
}

Further technical details

• Exception details:
  System.ObjectDisposedException
  HResult=0x80131622
  Message=IFeatureCollection has been disposed.
  Object name: 'Collection'.
  Source=Microsoft.AspNetCore.Http.Features
  StackTrace:
  at Microsoft.AspNetCore.Http.Features.FeatureReferences`1.ThrowContextDisposed() in /_/src/Http/Http.Features/src/FeatureReferences.cs:line 120

• ASP.NET Core version - 3.1.0

• Output of dotnet --info:
  dotnetInfo.txt

• The IDE is VS2019 Version 16.4.1

[Tratcher]

Do you have the full stacktrace for the exception?

Is this on IIS or Kestrel? Seems like IIS.

If you observe and categorize the failures as shown by HttpClient, what's the breakdown that timeout, receive 500s, etc.? This may be related to the client timing out and disconnecting. Are there any more interesting failures reported by the client?

Also, how does it behave if you switch to HTTP/2?

[analogrelay]

        services.AddSingleton<WeatherForecastController>();

Does it work if you remove this? I'm not sure Controllers are supposed to be singletons. (cc @rynowak)

[Jasdo]

        services.AddSingleton<WeatherForecastController>();

Does it work if you remove this? I'm not sure Controllers are supposed to be singletons. (cc @rynowak)

Yes, it works.
The problem is that it creates a new instance of the controller for each REST call, and I'm trying to avoid that. Of course I can move the part that I want to be a "singleton" to another class, but everything worked fine before we migrated to 3.1 from 2.1.
I assume it is related to this change in FeatureReferences.

[analogrelay]

The problem is that it creates a new instance of the controller for each REST call, and I'm trying to avoid that.

Why are you trying to avoid that? If you need a singleton, it should be a service consumed by the controller, not the controller itself.

[Tratcher]

I checked with MVC and controllers are not supported as singletons. They have request state, so even if you didn't hit issues like this, you'd still have concurrency problems.

[Jasdo]

The problem is that it creates a new instance of the controller for each REST call, and I'm trying to avoid that.

Why are you trying to avoid that? If you need a singleton, it should be a service consumed by the controller, not the controller itself.

Yes, this is how it is implemented now in our code, the thing is that using the controller as a singleton worked until we migrated from ASP .NET Core 2.1 to 3.1.

[Jasdo]

@Tratcher, @anurse
Thank you for your help!