C# .NET WinForms App - Update UI while in a long operation

Hi All,

I am using VisualStudio 2010 - Framework 4.0.

In my C# .NET WinForms application, I have a long process running on click of a button.

I need to update the status of operation in the UI. I am working on an existing code so I cannot disturb the existing functionality.

My problem is that the long running method sits in a different project (P1) and the UI in other(P2). Also there is an interface which connects these two which sits in another project (P3).

So my requirement is to update a label in the UI (P2.Label) from P1.Method through P3.Interface.

Is there anyway I can update UI without threading? If threading/background process is the only workaround for this, then please explain it in my case. I am not comfortable with interfaces. What about using INotifyChanged which I am using in WPF?

Hope I explained well.

Thanks

Bian