c#: How to handle finalizer exceptions from a 3rd-party library?

Question

Finalizers are always called by .net framework, so the sequence could be out of control; and even if the constructor failed, the destructor still can be triggered.

This could bring troubles, when such finalizer exceptions come from a 3rd-party library: I can't find a way to handle them!

For example, in the code below, although class A's constructor always throw an exception and fail, finalizer of A will be triggered by the .net framework, also ~B() is called as A has a property of B type.

class Program // my code
{
    static void Main(string[] args)
    {
        A objA;
        try
        {
            objA = new A();
        }
        catch (Exception)
        {
        }

        ; // when A() throws an exception, objA is null

        GC.Collect(); // however, this can force ~A() and ~B() to be called.

        Console.ReadLine();
    }
}

public class A  // 3rd-party code
{
    public B objB;

    public A()
    {
        objB = new B(); // this will lead ~B() to be called.
        throw new Exception("Exception in A()");
    }

    ~A() // called by .net framework
    {
        throw new Exception("Exception in ~A()"); // bad coding but I can't modify
    } 
}

public class B // 3rd-party code
{
    public B() { }

    ~B() // called by .net framework
    {
        throw new Exception("Exception in ~B()"); // bad coding but I can't modify
    } 
}

If these are my code, it is a bit easier - I can use try-catch in finalizers, at least I can do some logging - I can allow the exception to crash the program, to discover the error asap - or if I want to "tolerate" the exception, I can have a try-catch to suppress the exception, and have a graceful exit.

But if A and B are classes from a 3rd-party library, I can do nothing! I can't control the exception to happen, I can't catch them, so I can't log it or suppress it!

What can I do?

Answer 1

Sounds like the 3rd party utility is poorly written. :)

Have you tried catching it using AppDomain.UnhandledException?