Services added with AddHostedService are unable to resolve registrations in ASP.NET Core 3

Description of the bug

Adding a service with AddHostedService<T>() is unable to resolve types registered with Simple Injector in ASP.NET Core 3. The same code worked in 2.2.

Trying to step through the code it appears that services added with AddHostedService() are being started (and subsequently resolved) earlier in Core 3 than in 2.2, causing registrations to not yet have been added. The Startup.Configure() method is not hit at the time the exception is raised.

Moving the registrations to occur at the end of ConfigureServices() doesn’t help, as despite it fixing the missing registrations it is not possible to then call app.UseSimpleInjector() in Configure() as the hosted service being resolved before Configure() is called locks the container:

The container can’t be changed after the first call to GetInstance, GetAllInstances, Verify, and some calls of GetRegistration. Please see https://simpleinjector.org/locked to understand why the container is locked. The following stack trace describes the location where the container was locked:

at SimpleInjector.Container.GetInstance[TService]()
at SimpleInjector.SimpleInjectorGenericHostExtensions.<>c__DisplayClass0_0`1.<AddHostedService>b__0(IServiceProvider _)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[TStateMachine](TStateMachine& stateMachine)
at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[TStateMachine](TStateMachine& stateMachine)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
at Test.Web.Program.Main(String[] args) in E:\projects\test\src\backend\Test.Web\Program.cs:line 14

Expected behavior

Type of HostedService is resolved.

Actual behavior

Exception:

The container can’t be changed after the first call to GetInstance, GetAllInstances, Verify, and some calls of GetRegistration. Please see https://simpleinjector.org/locked to understand why the container is locked. The following stack trace describes the location where the container was locked:

To Reproduce

Replace the default Startup with the following:

public class HostedService : IHostedService
{
    public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}

public class Startup
{
    private readonly Container container = new Container();

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

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews();

        services.AddSimpleInjector(this.container, options =>
        {
            options.AddHostedService<HostedService>();
        });
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.ApplicationServices.UseSimpleInjector(this.container);

        app.UseStaticFiles();

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

Additional context

• Simple Injector 4.7.1
• .NET Core 3

[dotnetjunkie]

btw thank you for this detailed and excellent bug report. This is how I rather see everyone pointing their bugs and questions.

[dotnetjunkie]

Crêpe! Yet another unfortunate breaking change in ASP.NET Core v3. I will investigate this and report back to you when I found a workaround or have a fix available. Might take a few days for me to get to this point though.