In self-hosted OWIN Web API, how to run code at shutdown?

Question

I am self-hosting a OWIN Web API using these code snippets:

class Startup
{
    public void Configuration(IAppBuilder appBuilder)
    {
        var config = new HttpConfiguration();
        var route = config.Routes.MapHttpRoute("DefaultApi", "{controller}");
        appBuilder.UseWebApi(config);
    }
}

WebApp.Start<Startup>("http://localhost:8080")

I would like to run some code when my Web API service shuts down. I'm looking for something like HttpApplication.Application_End, a Disposed event, or a well-placed override void Dispose().

How do I run code when the Web API service shuts down?

Answer 1

This can be achieved by getting the host's cancelation token and registering a callback with it like so

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        var context = new OwinContext(app.Properties);
        var token = context.Get<CancellationToken>("host.OnAppDisposing");
        if (token != CancellationToken.None)
        {
            token.Register(() =>
            {
                // code to run
            });
        }
    }
}

I was told by someone on the Katana team that this key is for host specific functionality and therefore may not exist on all hosts. Microsoft.Owin.Host.SystemWeb does implement this, but I'm not sure about the others.

The easiest way to verify if this will work for you is to check app.Properties for the host.OnAppDisposing key.

Answer 2

I think there is a better way to get the CancellationToken:

var properties = new AppProperties(app.Properties);
CancellationToken token = properties.OnAppDisposing;

AppProperties is under namespace Microsoft.Owin.BuilderProperties, which comes from this nuget package: http://www.nuget.org/packages/Microsoft.Owin/

The description of property OnAppDisposing says:

Gets or sets the cancellation token for “host.OnAppDisposing”.

Please refer to: http://msdn.microsoft.com/en-us/library/microsoft.owin.builderproperties.appproperties%28v=vs.113%29.aspx

Answer 3

This is the same as arthas's answer but I've made it into an extension method

public static IAppBuilder RegisterShutdown(this IAppBuilder app, Action callback)
{
    if (app == null)
    {
        throw new ArgumentNullException(nameof(app));
    }

    var properties = new AppProperties(app.Properties);
    var token = properties.OnAppDisposing;

    if (token != CancellationToken.None)
    {
        token.Register(callback);
    }

    return app;
}

Because then you can easily register shutdown actions like this

app.RegisterShutdown(() => Serilog.Log.CloseAndFlush());