C# interview question

Question

This is an interview question I need help with.

You have the following ASP.NET code-behind class:

public partial class Page1 : Page 
{
    private string _value;

    public Page1() 
    {
        if (DateTime.Now.Ticks % 10 == 0)
            _value = "Test";
    }       

    ~Page1() 
    {
        if(_value.Equals("Test"))
            _value = string.Empty;      
    }
}

Any time someone requests this page, the w3wp.exe process terminates unexpectedly.

• Why does this occur versus the user seeing a yellow screen of death (default ASP.NET error page)?

• Why is there always an OutOfMemoryException present on the managed heap?

Answer 1

Hint: never throw exceptions in a destructor/finalizer or you will kill the thread on which the GC runs and without GC things might get ugly.

While there was some tolerance in .NET 1.1 towards exceptions thrown in background threads which were consumed and wouldn't bring the hosting process down that's no longer the case starting from CLR 2.0. Quote from the doc:

If Finalize or an override of Finalize throws an exception, and the runtime is not hosted by an application that overrides the default policy, the runtime terminates the process and no active try-finally blocks or finalizers are executed. This behavior ensures process integrity if the finalizer cannot free or destroy resources.

Throwing an exception in a finalizer is fatal.