Question

newbie here, sorry if this is an obvious question.

I’ve read from this page: http://code.google.com/p/autofac/wiki/NewInV2

In Autofac 1, weak references are held by the container. This makes sense if the objects being referenced use disposal to release GC/finalizer resources, but if the dispose method contains application logic then GC timing could introduce unexpected behaviour.

Autofac 2 holds normal references. To opt out of this behaviour and mange disposal manually, use the ExternallyOwned registration modifier.

Is that mean when I need to release an object that is resolved by Autofac to the GC, I cannot simply say:

a = null;

because Autofac holds a strong reference to the object. Instead, I should use Owned<>:

public class MyClass
{
    public MyClass(Owned<A> a)
    {
        a.Value.Dosomething();
        a.Dispose();
    }
}

or use the ExternallyOwned registration modifier:

builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).ExternallyOwned();

later on, I should be able to use a = null to release the object to the GC.

Is that right?

Thanks!

Answer 1

By default, you don’t need to dispose anything – Autofac will automatically identify and dispose any IDisposable instances it created when their containing lifetime scope is disposed.

You only need to use Owned<T> or ExternallyOwned() if you have a reason to manage the lifetime of the object manually. If you resolve an Owned<T> then you should call t.Dispose() yourself – the common usage pattern is to take a dependency on a factory delegate:

public class MyClass
{
    private Func<Owned<User>> myDisposableFactory;

    public MyClass(Func<Owned<User>> myDisposableFactory)
    {
        this.myDisposableFactory = myDisposableFactory;
    }

    public void DoSomething()
    {
        using (var disposable = this.myDisposableFactory())
        {
            // ...
            disposable.Dispose();
        }
    }
}

If you register a type as ExternallyOwned() then Autofac will not dispose of any resolved instance when the containing lifetime scope ends – it’s up to you to manage it.

Take a look at Nicholas Blumhardt’s article on lifetimes for more information.