Autofac Lifetime Management

Question

I'm working on an ASP.NET MVC project that support external plugins, now, I'm moving from Unity to Autofac and I need to wrap the lifetime objects of Autofac so the plugins won't have to reference it, in Unity I could do something this.

public sealed class UnityScopeFactory : IDependencyScopeFactory
{
    private HttpRequestScope _httpRequest;

    private SingletonScope _singleton;

    private TransientScope _transient;

    public IDependencyScope HttpRequest()
    {
        return _httpRequest ?? (_httpRequest = new HttpRequestScope());
    }

    public IDependencyScope Singleton()
    {
        return _singleton ?? (_singleton = new SingletonScope());
    }

    public IDependencyScope Transient()
    {
        return _transient ?? (_transient = new TransientScope());
    }

    private class HttpRequestScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new HttpPerRequestLifetimeManager();
        }
    }

    private class SingletonScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new ContainerControlledLifetimeManager();
        }
    }

    private class TransientScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new TransientLifetimeManager();
        }
    }
}

I made similar thing in Autofac but I'm not sure whether it's the correct way to do that, I looked into the RegistrationBuilder of Autofac which is (unfortunately) internal and I came up with this.

public class AutofacScopeFactory : IDependencyScopeFactory
{
    private HttpRequestScope _httpRequest;

    private SingletonScope _singleton;

    private TransientScope _transient;

    public IDependencyScope HttpRequest()
    {
        return _httpRequest ?? (_httpRequest = new HttpRequestScope());
    }

    public IDependencyScope Singleton()
    {
        return _singleton ?? (_singleton = new SingletonScope());
    }

    public IDependencyScope Transient()
    {
        return _transient ?? (_transient = new TransientScope());
    }

    private class HttpRequestScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new CurrentScopeLifetime();
        }
    }

    private class SingletonScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new RootScopeLifetime();
        }
    }

    private class TransientScope : IDependencyScope
    {
        public object CreateScope()
        {
            return new CurrentScopeLifetime();
        }
    }
}

Also, after I got this to work, how can I use pass it to the ContainerBuilder?

In Unity I could do something like this.

public sealed class UnityDependencyContainer : IDependencyContainer
{
    private readonly IUnityContainer _container;

    public UnityDependencyContainer()
    {
        _container = new UnityContainer()
    }

    public void Register<TContract, TImplementation>(IDependencyScope scope) where TImplementation : TContract
    {
        LifetimeManager manager = scope.CreateScope() as LifetimeManager;

        if (manager != null)
        {
            _container.RegisterType<TContract, TImplementation>(manager);
        }
    }
}

How do I pass an instance of IComponentLifetime to the method chain? is it a dead end?

public class AutofacContainer : IDependencyContainer
{
    private static readonly ContainerBuilder Builder;

    static AutofacContainer()
    {
        Builder = new ContainerBuilder();
    }

    public void RegisterType<TContract, TImplementation>(IDependencyScope scope) where TImplementation : TContract
    {
        IComponentLifetime manager = scope.CreateScope() as IComponentLifetime;

        if (manager != null)
        {
            Builder.RegisterType<TImplementation>().As<TContract>();
        }
    }
}

Answer 1

Autofac doesn't separate scopes quite the way you have it outlined, so you might be trying to fit a square peg in a round hole.

Autofac scopes are more hierarchical. Any lifetime scope can spawn a child transient scope. For example, you might see...

• Container/root lifetime
  • HttpRequest scope
    • Small task-specific transient scope

You can "tag" a scope and register components to a specific named/tagged scope - that's how the HttpRequest scope works. It gets "tagged" with a special identifier.

When you resolve objects is when it determines which lifetime scope owns it. Resolving happens from the most-nested scope. In the above hierarchy, you resolve items from the small task-specific transient scope whether they're singletons, request scoped, or whatever. When the singleton gets resolved, it will search up the lifetime scope stack and automatically assign "ownership" of the object to the root lifetime scope. When a per-request item gets resolved, it searches up the stack for the lifetime scope with the special "HTTP request" identifier and assigns ownership there. Factory-scoped items are resolved in the current lifetime scope.

Note: That discussion is a gross oversimplification of how it works. There is documentation explaining the lifetime scope mechanism on the Autofac site.

Point being, I see some things in the above design that don't really "jive" with the way Autofac does stuff.

The DependencyScopeFactory can't create its own transient or HttpRequest scopes. There are specific lifetime management components that start and end the HttpRequest scope, so you'd need to use those; there is no 'global' transient scope, so you can't really just create one.

HttpRequest scope, assuming you're using MVC, would look more like...

public ILifetimeScope HttpRequestScope
{
  get { return AutofacDependencyResolver.Current.RequestLifetime; }
}

There's no analog for a transient scope because usage on that is supposed to be inline:

using(var transientScope = parentScope.BeginLifetimeScope())
{
  // Do stuff and resolve dependencies using the transient scope.
  // The IDisposable pattern here is important so transient
  // dependencies will be properly disposed at the end of the scope.
}

When you register components, you don't register them "into a lifetime scope." You actually register them into a component registry and part of the component registration includes the ownership information about the lifetime of the component once it's resolved.

var builder = new ContainerBuilder();

// This component is factory-scoped and will be "owned" by whatever
// lifetime scope resolves it. You can resolve multiple of these
// in a single scope:
builder.RegisterType<FirstComponent>().As<ISomeInterface>();

// This component is a singleton inside any given lifetime scope,
// but if you have a hierarchy of scopes, you'll get one in each
// level of the hierarchy.
builder.RegisterType<SecondComponent>().InstancePerLifetimeScope();

// This component will be a singleton inside a specifically named
// lifetime scope. If you try to resolve it in a scope without that
// name, it'll search up the scope stack until it finds the scope
// with the right name. If no matching scope is found - exception.
builder.RegisterType<ThirdComponent>().InstancePerMatchingLifetimeScope("scopename");

// This is a per-HTTP-request component. It's just like the
// above InstancePerMatchingLifetimeScope, but it has a special
// tag that the web integration knows about.
builder.RegisterType<FourthComponent>().InstancePerHttpRequest();

If you're trying to make a container/registration agnostic interface, it wouldn't need a "lifetime scope manager" - instead, you'd need to pass some parameters indicating the intended lifetime scope and do the appropriate registration syntax (above) based on the incoming parameters.

Again, I'd recommend you check out that documentation.

Also, if you're using Unity, Autofac does have an Enterprise Library Configurator package that allows you to configure Autofac in a Unity style (since that's how EntLib likes to do things). That might be something to check out.

If you don't need to use Unity syntax at all... I'd recommend just moving to do things the native Autofac way. Trying to make one container look and act like another is a pretty painful endeavor.

Assuming your plugins are in separate assemblies or whatever, you could easily take advantage of some of the nice assembly-scanning syntax along with Autofac modules and hook up your plugins that way.