Autofac Lifetimes and the Default Provider within a Matching Lifetime Scope

Question

I have an ASP.NET MVC web application using Autofac for dependency injection. Occasionally, this web application will start a thread to do some work separate from the request thread. When this background thread starts up, it establishes a new Autofac lifetime scope from the root container and runs some action.

public IAsyncResult Run<T>(Action<T> action)
{
    var NewTask = System.Threading.Tasks.Task.Factory.StartNew(() =>
    {
        using (var Scope = Runtime.Container.BeginLifetimeScope())
        {
            var Input = Scope.Resolve<T>();
            action(Input);
        }
    });

    return NewTask;
}

One of my dependencies registered with Autofac has two different implementations: one appropriate for http-request lifetimes and another appropriate for all other lifetimes. I tried to register them as follows:

builder
.Register(c => new Foo())
.As<IFoo>()
.InstancePerLifetimeScope();

builder
.Register(c => new FooForHttp(HttpContext.Current))
.As<IFoo>()
.InstancePerMatchingLifetimeScope(WebLifetime.Request);

Autofac selects FooForHttp for http requests (as expected). However, when my background thread spins up, any attempt to resolve IFoo results in an exception:

No scope with a Tag matching 'httpRequest' is visible from the scope in which the instance was requested. This generally indicates that a component registered as per-HTTP request is being reqested by a SingleInstance() component (or a similar scenario.) Under the web integration always request dependencies from the DependencyResolver.Current or ILifetimeScopeProvider.RequestLifetime, never from the container itself.

I know that Autofac always uses the last registered provider as the default provider for a particular component. I made an assumption here that it would use the last registered suitable provider.

Am I missing something, or is there a better approach to selecting a provider based on the tag of the current lifetime scope?

Answer 1

Register the web Foo as normal, but don't register the other Foo. When creating the lifetime scope for the async task, use the overload of BeginLifetimeScope() that takes an action on ContainerBuilder. Register the background Foo in this action (b => b.Register()) and this should override the web one. (Small keyboard here sorry :))

Answer 2

This can also be solved by using a tagged life time scope. Register your fisrt Foo as instance of your tagged scope:

builder.RegisterType<Foo>().As<IFoo>.InstancePerMatchingLifetimeScope("YourScopeTag");

And create the scope with the same tag you registered your dependencie:

  using (var Scope = Runtime.Container.BeginLifetimeScope("YourScopeTag"))
        {
            var Input = Scope.Resolve<T>();
            action(Input);
        }

Haven't tested it, but it should work

http://docs.autofac.org/en/latest/lifetime/instance-scope.html#instance-per-matching-lifetime-scope