Resolution failure when resolving multiple dependencies with Diagnostic extension enabled

[delpher]

Description

When using Diagnostic container extension resolving class that requires IEnumerable of dependencies registered by name failes with AccessViolationException.

Observed in Unity 5.11.1

To Reproduce

    public class ResolutionTests
    {
        [Fact]
        public void Resolve_Multiple_With_Diagnostics_Enabled()
        {
            var container = new UnityContainer();

            container.AddNewExtension<Diagnostic>();
            
            container.RegisterType<IInterface, Implementation1>("strategy1");
            container.RegisterType<IInterface, Implementation2>("strategy2");

            container.RegisterType<IConsumer, Consumer>();

            container.Resolve<IConsumer>().Consume();
        }
    }

    public interface IInterface
    {
    }

    public class Implementation2 : IInterface
    {
    }

    public class Implementation1: IInterface
    {
    }

    public interface IConsumer
    {
        void Consume();
    }

    public class Consumer : IConsumer
    {
        private readonly IEnumerable<IInterface> _interfaces;

        public Consumer(IEnumerable<IInterface> interfaces)
        {
            _interfaces = interfaces;
        }

        public void Consume()
        {
            _interfaces.ToArray();
        }
    }

Additional context

Depending on container configuration other possible exceptions can occur: NullReferenceException, StackOverflowException has also been observed.

[abakumov-v]

+1

After update to version 5.11.1 we found on our dev/prod envrionments an AccessViolationException. In our case this exception occured when working with MediatR - for example:

await _mediator.Send(new PutLogItemCommand()
{
    LogItems = request?.Log.Select(ToLogItem).ToList()
});

MediatR was configured like this: https://github.com/jbogard/MediatR/blob/master/samples/MediatR.Examples.Unity/Program.cs

We spent a lot of time searching for the problem, since AccessViolationException not caught try-catch. And how catch this exception, we don't know...

UPD: if we comment Diagnostic extension, all works fine.

[BryantL]

I've come across the same issue upgrading to 5.11.x.

The issue relates to the change in behavior of IEnumerable[T] where it is now deferred resolved.
When diagnostics is turned on, the Parent pointer on ContextBuilder is used. This mechanism (of using the Parent pointer) only works because the "parent" ContextBuilder still exists on the stack of a method further up the call stack.
With deferred execution the call stack (and hence the stacks of the methods) is torn down by the time of actually resolution and so the pointer is dangling.

The solution (I believe) is to resolve the items of the enumerable in a similar way to Func[T] resolves them which calls UnityContainer.Resolve inside the func (thereby starting a new callstack).
I'll look to get a PR in soon (when I'm not crazy busy) that makes this modification.

[rjgotten]

Looks like this might be what we're hitting as well, by using Unity as the backing DI container for an ASP.NET Core 3 solution.

Whenever we enable diagnostics, our applications come crashing down with an access violation when attempting to resolve IHost. Presumably something in its build-up is hitting multiply-registered entities.

Good to hear that there will hopefully be a solution soon, because without diagnostics enabled, new versions of Unity reveal preciously little (basically nothing usable) that can assist in tracking down build-up errors.

[karelkral]

I spent about 7 hours while resolving bug in registration, which was my fault. If Diagnostic was functional, it can be solved in 5 minutes. But diagnostic was crashing with access violation as described here.

[BryantL]

I've submitted a PR with a proposed fix

[anlau]

Any update on this issue or on the proposed fix? It still happens in Unity.Container 5.11.5.

[ENikS]

Working on my COVID immunity, antibodies and all. It might take a while...

[jarikp]

Working on my COVID immunity, antibodies and all. It might take a while...

Oh, sorry to hear - hope you feel better soon!