How can I observe changes to an underlying array?

I suppose it's pretty safe to assume that you can't know approximately what block of array elements is most likely to change, so...

You could kind of load-balance by divvying up index blocks among several threads. Since the number of elements is variable, I would setup some way to determine how big each array index block is on a per-thread basis, so for example, if you have 5000 elements, you could create 10 threads, and assign a block of 500 elements to each thread. This would make the change detection somewhat faster.

If you have over 50k elements, you could create more threads and/or watch larger blocks per thread.

It would be a challenging task to marshall all of these things, but I would personally get a real kick out of having to come up with a solution, if it were me.

It's too bad you're not using .Net 4, because it supports parallel tasking on a multi-cpu machine, and it's built just for problems like this.

BTW, this load-balancing approach would still require you to wqrap the array in an ObservableCollection of integers, and update those integers from from the array. I would probably build my items like this:

public class ArrayItem : IObservable
{
    private Array[int] m_array = null;
    private int m_value;
 
    public int Value
    {
        get
        {
            return m_value;
        }
        set
        {
            m_value = value;
            OnPropertyChanged("Value");
        }
    }
 
    public int Index { get; set; }
     
    //--------------------------------------------------------------------
    public void OnPropertyChanged(string propertyName)
    {
        // blah blah
    }
 
    //--------------------------------------------------------------------
    public ArrayItem(Array[] int source, int index)
    {
        m_array = source;
        Index   = index;
        Value   = m_array[Index];
    }

 
    //--------------------------------------------------------------------
    // call this method from the thread when the array value changes
    public UpdateValue()
    {
        Value   = m_array[Index];
    }
}

Of course, you could probably avoid passing in the array if it's static and you can get to it anywhere in your app.