Question

I’ve been using this pattern to initialize static data in my classes. It looks thread safe to me, but I know how subtle threading problems can be. Here’s the code:

public class MyClass // bad code, do not use
{
    static string _myResource = "";
    static volatile bool _init = false;
    public MyClass()
    {
        if (_init == true) return;
        lock (_myResource)
        {
            if (_init == true) return;
            Thread.Sleep(3000); // some operation that takes a long time 
            _myResource = "Hello World";
            _init = true;
        }
    }
    public string MyResource { get { return _myResource; } }
}

Are there any holes here? Maybe there is a simpler way to do this.

UPDATE: Consensus seems to be that a static constructor is the way to go. I came up with the following version using a static constructor.

public class MyClass
{
    static MyClass() // a static constructor
    {
        Thread.Sleep(3000); // some operation that takes a long time 
        _myResource = "Hello World";
    }

    static string _myResource = null;

    public MyClass() { LocalString = "Act locally"; } // an instance constructor

    // use but don't modify
    public bool MyResourceReady { get { return _myResource != null; } }
    public string LocalString { get; set; }
}

I hope this is better.

Answer 1

You can use static constructors to intialize your static variables, which C# guarantees will only be called once within each AppDomain. Not sure if you considered them.

So you can read this: http://msdn.microsoft.com/en-us/library/aa645612(VS.71).aspx (Static Constructors)

And this: Is the C# static constructor thread safe?