Why this static constructor is not getting called?

Question

I am creating asp.net web service. I have one class, whose static constructor is not getting called when I try to initialize object of that class. I am not able to understand this behavior. Inside static constructor I am reading values from web.config file.

Here is part of code :

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class Service : System.Web.Services.WebService
{
    AppController extractor;

    public Service()
    {
        try
        {
            extractor = new AppController();
        }
        catch(Exception ex)
        {
            // I am not getting exception at this point.
        }
    }
}

public class AppController
{
    static string converterBatchFilePath = null;
    static string personalProfileOutputFolderPath = null;

    static AppController()
    {
        // reading some settings from web.config file
        try
        {
            converterBatchFilePath = ConfigurationManager.AppSettings["WordToTextConverterBatFilePath"];
        }
        catch(Exception ex)
        { // }
    }
    public AppController()
    {
        // do some initialization
    }
}

While debugging web service I noticed that only instance constructor is getting called and control never goes to static constructor.

Anyone know why this is happening?

I am using VS 2008 Express edition and C#.

EDIT

Actually this AppController is console based project. I have added that project as a reference inside Web service project and then using it. If I use AppController from command line, it works fine, but its not working from inside web service project.

Answer 1

Today my static initializer was not being called. It turns out static initializers are not called prior to accessing const members of a class.

Since const values are known at compile time this makes sense, but it means that the documentation which states "It is called automatically before ... any static members are referenced" is technically incorrect, at least when combined with @JonSkeet's assertion that "All constants declarations are implicitly static".

This program demonstrates the problem:

using System;

static class Program
{
    public static void Main()
    {
        Console.WriteLine("Constant={0}", Problem.Constant);
        Console.WriteLine("ReadOnly={0}", Problem.ReadOnly);
        Console.WriteLine("Field={0}", Problem.Field);
        Console.WriteLine("Property={0}", Problem.Property);
    }

    private static class Problem
    {
        public const int Constant = 1;
        public static readonly int ReadOnly = 2;
        public static int Field = 3;
        private static int mProperty = 4;
        public static int Property { get { return mProperty; } }

        static Problem()
        {
            Console.WriteLine("Problem: static initializer");
        }
    }
}

The output is:

Constant=1
Problem: static initializer
ReadOnly=2
Field=3
Property=4

(Tested against .NET 4.5.)

Answer 2

My guess is that it's called before you expected it to be called. If you have already debugged your site but not recycled the AppPool, it's very likely that the static constructor has already been run. Similarly anything that accesses any static members will also call the static constructor if it hasn't already been called.

Answer 3

A static constructor is used to initialize any static data, or to perform a particular action that needs performed once only. It is called automatically before the first instance is created or any static members are referenced.

Please note that a static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced. and the user has no control on when the static constructor is executed in the program.

Taken from MSDN's Static Constructors (C# Programming Guide) .

Answer 4

I suspect that your problem is caused by an exception being raised in your static constructor and being swallowed by the code that creates the instance.

Potentially even an exception in a static field initializer which are even harder to debug.

Perhaps enabling breaking on first-chance exceptions helps debugging the problem.

---

I would not put code that reads from a config file into a static constructor at all. I'd instead encapsulate all config dependent stuff you have in a class and pass an instance of that class into your constructor, probably using an IoC container.

This has a number of advantages:

• You can use different configurations in the same AppDomain at the same time
• You can use alternate ways of loading the configuration
• You don't need to do complex stuff that might fail in a static constructor. As you have seen static constructors tend to be problematic to debug, so I'd do only simple initializations that don't depend on external state there

(I know this is not an answer, but it's too long for a comment)

Answer 5

When I was trying to debug by placing a breakpoint on the line where the static field had referenced, I was not getting debug control on the static constructor.

I kept breakpoint on the static constructor entrance, removed the breakpoint from the line where the static field had referenced. Now Debug control started coming into the static constructor code.

This image shows how your editor with breakpoints would look like

Answer 6

Here's a quick sample I put together to get values from a config file in your extractor class, both in the static and instance constructors. This works for me -- compare it against what you're doing and see what's different:

public class Service : System.Web.Services.WebService
{
    AppController extractor;

    [WebMethod]
    public string HelloWorld()
    {
        extractor = new AppController();
        return AppController.staticString + " :: " + extractor.instanceString;
    }
}

class AppController
{
    public static string staticString;
    public string instanceString;

    static AppController()
    {
        staticString = System.Configuration.ConfigurationManager.AppSettings["static"];
    }
    public AppController()
    {
        instanceString = System.Configuration.ConfigurationManager.AppSettings["instance"];
    }
}

My web.config:

  <appSettings>
    <add key="static" value="blah blah"/>
    <add key="instance" value="ha ha"/>
  </appSettings>

My response:

<?xml version="1.0" encoding="UTF-8"?>
<string xmlns="http://tempuri.org/">blah blah :: ha ha</string>