Static instance, desctructor never called

Question

Please see code below. The destructors are never called. Anyone know why and how this can be rectified?

public partial class Form1 : Form
{
    private Goo goo;

    public Form1()
    {
        InitializeComponent();

        goo = Goo.GetInstance();         
    }
}

public class Goo
{
    private foo f = new foo();
    private static Goo goo;
    private Goo()
    {}

    public static Goo GetInstance()
    {
        if(goo!=null)
        {
            goo = new Goo();
        }
        return goo;
    }

    ~Goo()
    {

    }
}

class foo
{
    ~foo()
    {

    }
}

Answer 1

Objects referenced by static fields are not simply finalized unless you clear (set to null) the field - and even then it is non-deterministic and not guaranteed. Static fields count as root objects.

When (and why) would you expect this to be collected/finalized? It is still accessible...

Answer 2

Objects referenced by static fields are always reachable (assuming no class unloading or any other GC funkiness) and will never be collected.

Answer 3

Even though you might expect the finalizer on static objects to run when the process is shutdown, there are no guarantees there either:

• http://blogs.msdn.com/cbrumme/archive/2004/02/20/77460.aspx (look at the section titled "V1 & V1.1 Finalization Guarantees"). I'm not sure how much of this has changed in .NET 2.0 or later.

Answer 4

That's not a destructor. It's a finalizer. That's a different thing. As the other two have said, because this is a static, it will never be collected, hence the finalizer will never run.