We Keep Coding

Akka.net deadlocking issue with ActorSelection

Having an issue with akka.net. I need to access an actor which I have already created with a specific name. I can retrieve the actor from IActorContext but I am struggling to access it from the ActorSystem.
I have created a method called GetOrCreateActor which attempts to get the actor using ActorSelection. If it doesn't exist, the catch creates a new actor with the name. If it does exist, I want it to return the reference. However, it never returns from '.Result'. Assuming this could be some sort of deadlocking issue.
public static IActorRef GetOrCreateActor<T>(this ActorSystem actorSystem, string actorPath, string name = null) where T : ActorBase
{
try
{
return actorSystem.ActorSelection(actorPath).ResolveOne(TimeSpan.FromSeconds(1)).Result;
}
catch
{
return actorSystem.ActorOf(actorSystem.DI().Props<T>(), name);
}
}
Edit
I've tried to include a simplified version of the calling code below.
The actor system is created in an IOC container using AutoFac (ExampleActor is the ReceiveActor I am trying to access):
containerBuilder.RegisterAssemblyTypes(typeof(ExampleActor).Assembly).Where(x => x.Name.EndsWith("Actor"));
var lazyContainer = new Lazy<IContainer>(() => containerBuilder.Build());
containerBuilder.Register(c =>
{
var system = ActorSystem.Create("ExampleActorSystem");
new AutoFacDependencyResolver(lazyContainer.Value, system);
return system;
}).As<ActorSystem>().SingleInstance();
return lazyContainer.Value;
ActorSystem is then injected into another class, where I call the GetOrCreateActor method (via the Execute method):
public class ExampleCommand : IExampleCommand
{
private readonly ActorSystem _actorSystem;
public ExampleCommand(ActorSystem actorSystem)
{
_actorSystem = actorSystem;
}
public void Execute()
{
SendMessage();
}
private void SendMessage()
{
string message = new Message();
_actorSystem.GetOrCreateActor<ExampleActor>("akka://ExampleActorSystem/user/ExampleActor", "ExampleActor").Tell(message);
}
}
The above command would be called from a RESTful endpoint
public ExampleGetModule(IExampleCommand exampleCommand)
{
Get["/api/createExample"] = parameters =>
{
exampleCommand.Execute();
};
}

Your deadlocking issue looks more like it has to do with how you're using your container than it does Akka.NET:
var lazyContainer = new Lazy<IContainer>(() => containerBuilder.Build());
containerBuilder.Register(c =>
{
var system = ActorSystem.Create("ExampleActorSystem");
new AutoFacDependencyResolver(lazyContainer.Value, system);
return system;
}).As<ActorSystem>().SingleInstance();
In terms of what can go wrong here, self-referential Lazy<T> types are an infamous source of race-conditions. You should not be calling lazyContainer.Value inside of this registration method if the output of containerBuilder.Build depends on the input of containerBuilder.Register.
Last thing is to use step-through debugging to make sure that your application actually calls into the ResolveOne method here - if you're not getting a timeout exception back then it means that your application is deadlocking on producing the actor system (because of how DI is configured).

Tell if Ninject convention bind failed

I am using Ninject.Extensions.Conventions to add bindings dynamically. The .dll names to load are stored in configuration. If the configuration is incorrect and the .dll can not be loaded it would be good to know about that. Currently any failure to load a .dll is not bubbled up. For example, if I try to load a potato there is no error I can catch:
foreach (var customModule in customModuleConfigs)
{
KeyValuePair<string, KVP> module = customModule;
_kernel.Bind(scanner => scanner
.From(module.Value.Value)
.SelectAllClasses().InheritedFrom<ICamModule>()
.BindAllInterfaces());
// I need to know this failed
_kernel.Bind(scanner => scanner
.From("potato")
.SelectAllClasses().InheritedFrom<ICamModule>()
.BindAllInterfaces());
}
Is there a way to know I have a bad configuration? In the IntelliTrace window I see an exception thrown but caught before it bubbles up.

You'll need to do the loading of the Assembly yourself, then you can control whether there is an exception thrown. Use the
From(params Assembly[] assemblies) overload.
Load the assembly by either using Assembly.LoadFrom() or Assembly.Load.

You could create a wrapper around the AllInterfacesBindingGenerator class and use this to count the generated bindings:
public class CountingInterfaceBindingGenerator : IBindingGenerator
{
private readonly IBindingGenerator innerBindingGenerator;
public CountingInterfaceBindingGenerator()
{
this.innerBindingGenerator =
new AllInterfacesBindingGenerator(new BindableTypeSelector(), new SingleConfigurationBindingCreator());
}
public int Count { get; private set; }
public IEnumerable<IBindingWhenInNamedWithOrOnSyntax<object>> CreateBindings(Type type, IBindingRoot bindingRoot)
{
this.Count++;
return this.innerBindingGenerator.CreateBindings(type, bindingRoot);
}
}
Usage:
var kernel = new StandardKernel();
var bindingGenerator = new CountingInterfaceBindingGenerator();
kernel.Bind(b =>
{
b.From("potato")
.SelectAllClasses()
.InheritedFrom<ICamModule>()
.BindWith(bindingGenerator);
});
if (bindingGenerator.Count == 0)
// whatever
This is probably longer than your current code, but it would allow further customization of the bindings that have been created.

Start WPF app from unit test in its own AppDomain

I am trying to run a WPF App from nunit. Since I only can run one App per AppDomain I instantiate a new AppDomain per acceptance test. When I do that, I run into serialization exceptions.
namespace Tests
{
[TestFixture, RequiresSTA, Serializable]
public class ApplicationTests
{
private MainWindow mainWindow;
private bool guiVisible;
private App app;
[TestCase("app domain name for instance of App")]
[TestCase("app domain name for another instance of App")]
public void ApplicationTest(string name)
{
AppDomain appDomain = AppDomain.CreateDomain(name);
//appDomain.ExecuteAssembly(#"C:\Users\bp\Documents\Visual Studio 2013\Projects\WpfApplication1\WpfApplication1\bin\Debug\WpfApplication1.exe");
CrossAppDomainDelegate action = () =>
{
app = new App();
app.InitializeComponent();
app.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(() => AppOnActivated(null, null)));
app.Run();
};
appDomain.DoCallBack(action);
}
private void AppOnActivated(object sender, EventArgs eventArgs)
{
if (!guiVisible)
{
mainWindow = (MainWindow)Application.Current.MainWindow;
mainWindow.ButtonViewModel = new ButtonViewModel();
mainWindow.ButtonViewModel.Name = "bla";
guiVisible = true;
}
app.Shutdown();
}
}
}
The exception I receive now:
System.Runtime.Serialization.SerializationException : Type is not
resolved for member 'Tests.ApplicationTests,Tests, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=null'.
I made the test class [Serializable] which does not help either.
Help is very much appreciated. I just want to start my WPF application from an NUnit test so that I can write acceptance tests for my application. I keep running into different walls and eventually whatever path I choose seems to lead to a dead end...
Many thanks in advance,
Bas

AppDomains are software-isolated processes in .NET. This means you can't just reference objects belonging to one AppDomain from another. Objects can be either copied by value (serialization) or by reference using MarshalByRefObject. Since WPF's objects are neither of those, you can't move them around AppDomains.
For your your testing purposes, you could use a simpler approach: run everything within the new AppDomain, and use the SetData and GetData methods to transfer data to assert on.
[TestCase("app domain name for instance of App")]
[TestCase("app domain name for another instance of App")]
public void ApplicationTest(string name)
{
AppDomain appDomain = AppDomain.CreateDomain(name,
AppDomain.CurrentDomain.Evidence,
AppDomain.CurrentDomain.SetupInformation);
appDomain.DoCallBack(StartApp);
Assert.IsTrue((bool)appDomain.GetData("GuiVisible"));
AppDomain.Unload(appDomain);
}
// using a static method instead of a lambda makes sure
// you haven't captured anything
private static void StartApp()
{
app = new App();
app.InitializeComponent();
app.Dispatcher.BeginInvoke(DispatcherPriority.Loaded,
new Action(() => AppOnActivated()));
app.Run();
}
private static void AppOnActivated()
{
var mainWindow = (MainWindow)Application.Current.MainWindow;
mainWindow.ButtonViewModel = new ButtonViewModel();
mainWindow.ButtonViewModel.Name = "bla";
AppDomain.CurrentDomain.SetValue("GuiVisible") = true;
app.Shutdown();
}

How can a component provide other components?

I want to have a component register other components in the registry as / after it's constructed. Let's say I have the following components:
interface IConfiguration
{
string SourceDirectory { get; }
string TargetDirectory { get; }
// other primitive-typed configuration parameters
}
class FileConfiguration : IConfiguration
{
// read parameters from some config file
}
class SourceDirectoryWrapper
{
public byte[] ReadFile(string filename)
{
// read a file from the source directory
}
public string Directory { get; set; }
}
class TargetDirectoryWrapper
{
public byte[] WriteFile(string filename)
{
// write a file into the source directory
}
public string Directory { get; set; }
}
class DirectoryWrapperFactory
{
public DirectoryWrapperFactory(IConfiguration config)
{
var source = new SourceDirectoryWrapper {
Directory = config.SourceDirectory
};
var target = new TargetDirectoryWrapper {
Directory = config.SourceDirectory
};
}
}
The components FileConfiguration and DirectoryWrapperFactory can be registered as is usual.
However, what I'd like to accomplish is to somehow "outject" the source and target objects created in DirectoryWrapperFactory. The basic idea is that different environments might require different configuration providers. (And even if not, I think it's a good idea to put reading configuration parameters into a separate component.)
I'd also like to have SourceDirectoryWrapper and TargetDirectoryWrapper managed in the IoC container. In my case, mainly for convenience – I have an EventSource implementation that I need everywhere, so I inject it using property autowiring. Every object not in the IoC container needs to have it passed explicitly, which kind of bugs me.
So: is this possible with AutoFac? If so, how? I poked at the lifecycle events but most don't allow access to the registry after an object is built.

I don't quite understand why DirectoryWrapperFactory needs to exist. You could just register SourceDirectoryWrapper and TargetDirectoryWrapper directly as part of normal wireup:
builder.Register(c => new SourceDirectoryWrapper {
Directory = c.Resolve<IConfiguration>().SourceDirectory
});
builder.Register(c => new TargetDirectoryWrapper {
Directory = c.Resolve<IConfiguration>().SourceDirectory
});

Creating a wrapper over setup and teardown of AppDomain

using System;
using System.IO;
using System.Reflection;
using System.Text;
using MyApp.Logging;
namespace MyApp.SmsService.Common
{
public class MyAppAppDomain:MarshalByRefObject
{
private readonly AppDomainSetup domaininfo;
private readonly AppDomain appDomain;
public static string libDllPath;
public MyAppAppDomain(string appDomainName) //Constructor
{
//Setup the App Domain Parameters
domaininfo = new AppDomainSetup();
domaininfo.ApplicationBase = AppDomain.CurrentDomain.SetupInformation.ApplicationBase;
domaininfo.DisallowBindingRedirects = false;
domaininfo.DisallowCodeDownload = true;
domaininfo.ConfigurationFile = AppDomain.CurrentDomain.SetupInformation.ConfigurationFile;
// Create the application domain.
appDomain = AppDomain.CreateDomain(appDomainName, null, domaininfo);
//Set the dll path using Static class ref.
//Dependency resolution handler
appDomain.AssemblyResolve += LoadFromLibFolder; /*Exception*/
}
private static Assembly LoadFromLibFolder(object sender, ResolveEventArgs args)
{
if (libDllPath != null)
{
string assemblyPath = Path.Combine(libDllPath, new AssemblyName(args.Name).Name + ".dll");
if (File.Exists(assemblyPath) == false)
{
return null;
}
Assembly assembly = Assembly.LoadFrom(assemblyPath);
//Assembly dependancy resolved.
return assembly;
}
return null;
}
public Object getNewInstanceOf(string fullyQualifiedTypeName)
{
return appDomain.CreateInstanceAndUnwrap(Assembly.GetExecutingAssembly().FullName, fullyQualifiedTypeName);
}
public Type getTypeOf(string fullyQualifiedTypeName)
{
return getNewInstanceOf(fullyQualifiedTypeName).GetType();
}
public void unloadDomain()
{
AppDomain.Unload(appDomain);
}
}
}
The above class is a wrapper that I want to create to setup and teardown an application domain. However, in my webservice I am getting a FileNotFoundException [Failed to load a dll xyz.dll] whenever I am instantiating the object of MyAppAppDomain.
Following is the ex:
MyAppAppDomain.libDllPath = appDllLibPath; //Some directory other than bin.
pluginDomain = new MyAppAppDomain("SmsServicePlugins"); //Throws FileNotFoundException.
When I debug, I see that the line that caused the exception is the one marked above as /exception/, inside the constructor of MyAppAppDomain.
What is going wrong?
EDIT:
I was going through other articles and I read that objects cannot be visible across domains. This can only happen when the object can be serialized in both domains (use of MarshalByRefObject) and then can be accessed through proxies.
Would be of great help if someone can point out the issues in the above code. In the meanwhile I am attempting to learn more on Marshalling and Proxy-ing.

First problem is you are trying to doing everything inside app domain wrapper, it is really two different components. The first component you need is your object that you want to create inside your new app domain which inherits from MarshalByRefObject (or marked as Serializable). The other lives inside your current AppDomain and is used to create the new AppDomain.
Have a look at the msdn example to see what I mean.
However your error is probably more than likely that your path is wrong to your DLL. Could you show the full stack trace to show what line is throwing the exception?