I was just encountering a bug with using the System.Threading.Timer object in Silverlight for UnitDriven. It was very non-intuitive and sporadic so I thought I’d post some of my conclusions here just in case.

The problem was, that if I had a test that contained a BackgroundWorker that called Thread.Sleep(x) in it’s DoWork event, the timer callback would never get called. I would set the timer to fire in 5 seconds then call sleep for 30. The timer would only fire after the sleep was concluded.

I believe this is the case because Silverlight only has 1 background thread, or at least the Timer and the BackgroundWorker are sharing the same thread. So even though the timers timeout has expired it cannot get CPU time to do the work and fire the callback. The solution I came up with was to, instead of using a timer, simply call Application.Current.RootVisual.BeginInvoke(this.CheckForTimeout) and do the calculation myself. That worked like a charm.

So my conclusion is that getting yourself onto the UI thread in Silverlight is a more reliable way of guaranteeing CPU time since the UI thread is more likely to pumping continuously. Of course too much of that and everything will seem sluggish. What I really need is a backround work queue, or a dispatcher for a background thread in other words.

The book DSLs in Boo: Domain-Specific Languages in .NET written by Oren Eini writing as Ayende Rahien has finally shipped. The final version is available online at Manning Press and I highly recommend it.

I was one of the technical reviewers so I have already read this book and I can tell you first hand it’s definitely one for your book shelf. The first few chapters describe the generalities of DSLs and Boo then the subsequent chapters describe all of the details you might need to know to implement an internal DSL in your application.

If you’ve been wondering about the whole DSL thing, this book would be a good gateway to the world. It’ll stretch your brain and certainly expose you to some new ideas. In addition the author makes a good case for some practical business applications and introduces a new addition to the open source scene: Rhino DSL.

I also got an honorable mention in the acknowledgments section of the book and a special quote on the Manning Press web site that’s pretty cool! Check out it out!