ASP.NET Core: Singleton service not disposed of (Microsoft.Extensions.DependencyInjection) after closing the web browser

Question

I have a ASP.NET Core 6 Web API with this disposable service class:

public interface IMyService: IDisposable { }

public class MyService: IMyService
{
    public void Dispose() => Console.WriteLine("Disposing..."); // never called
}

In program.cs I have this service injected as a singleton:

builder.Services.AddSingleton<IMyService, MyService>();

According to all docs that I could find, the app should call MyService.Dispose() when it shuts down. However this doesn't happen.

What am I missing?

Steps to reproduce:

1. Create a ASP.NET Core WebAPI project using default template (VS2022)
2. At the end of program.cs add this code:

    public interface IMyService : IDisposable { }
   
    public class MyService : IMyService
    {
   
        public MyService()
        {
        }
   
        public void Dispose() => Console.WriteLine("Disposing..."); // never called
    }
   

3. Put a breakpoint on constructor and one on Dispose
4. Add this line somewhere at the top (after builder is created):

    // Add services to the container.
   
    builder.Services.AddSingleton<IMyService, MyService>();
   

5. In WeatherForecastController.cs change the constructor signature like this:

    public WeatherForecastController(
        ILogger<WeatherForecastController> logger, IMyService myService)
   

6. Run the app. In the browser click Get then Try it out then Execute
7. The break point in MyService constructor shd be hit
8. Close the browser. The Dispose breakpoint is not hit, Output message is not displayed

Answer 1

It looks like the problem was actually not closing the web app gracefully.If anyone is interested, here is how to gracefully shut down a web app:

• for VS2019 (and earlier) the process is described here: Gracefully stopping ASP.NET Core Web App (from within Visual Studio debugger), an IHostedService-related question
• for VS2022: when debugging, VS opens a separate window (Visual Studio Debugger Console Application Resources). Go to that console window and press Ctrl-C to stop the app.

Answer 2

How do you call this service in your project?

In general, you can use the using keyword to call this service:

using (MyService service = new MyService())
{
     service.xxxxxx();
}

In this way, The project will call Dispose() automatically when it shuts down.

But from your question, You are using

 AddSingleton<IMyService, MyService>() 

to register this server. So Dispose() method will only be called when the entire program is shut down. You can change AddSingleton to AddScoped, Then every time you send a new http reqest, you will find Dispose() method be called automatically.

(When using AddSingleton to register service, Only I shut down the project, The Dispose() method can be called automatically)

Answer 3

TLDR; When running the application as a web service (using IIS), it is the web server that decides whether the web application should be shut down. Closing a web browser will have no effect (unless you are running your application as a developer using the debugger).

Here is a minimal Console application that uses Microsoft.Extensions.DependencyInjection and demonstrates how Singleton services are disposed of when the container itself gets disposed of.

using System;
using Microsoft.Extensions.DependencyInjection;

var services = new ServiceCollection();

services.AddSingleton<IMyService, MyService>();

using (var container = services.BuildServiceProvider())
{
    container.GetRequiredService<IMyService>();
}

public interface IMyService : IDisposable { }

public class MyService : IMyService
{
    public void Dispose() => Console.WriteLine("Disposing...");
}

When running, this program gives the following output:

Disposing...

You can run this program yourself using .NET Fiddle: https://dotnetfiddle.net/S9gXA8.

Since ASP.NET Core disposed of the container when the application stops, you should see similar behavior. If this is not the case, this could have multiple causes, such as:

• You are aggressively stopping the application, for instance by stopping the debugger.
• The type MyService hasn't been created by the container before the application ends. Note that components are created lazily, even Singletons.
• The application or window closes before you have the time to view the output.
• The application is actually still running. When running the application as a web service (using IIS), it is the web server that decides whether the web application should be shut down. Closing a web browser will have no effect (unless you are running your application as a developer using the debugger).