Since is very common to use coroutines for spawn non blocking asynchronous activities in Caliburn Micro (CM), I wrote a simple base class than executes the computation via a BackgroundWorker and ensure the result “Completed” is fired on the same thread who start the call, typically, but not necessary, the UI thread. Here the class:

public abstract class AbstractBackgroundAction:IResult
   {
       abstract protected void OnExecute(ActionExecutionContext context);
       #region IResult Members

       public event EventHandler<ResultCompletionEventArgs> Completed = delegate { };

       public void Execute(ActionExecutionContext context)
       {
           using( BackgroundWorker bw = new BackgroundWorker() )
           {
               Exception exception=null;
               bw.DoWork+=(s,e)=>
                   {
                       try
                       {
                           OnExecute(context);
                       }
                       catch (Exception workException)
                       {
                           exception = workException;
                       }
                   };
               bw.RunWorkerCompleted+=(s,e)=>
                   {
                       Completed(this, new ResultCompletionEventArgs { Error=exception });
                   };
               bw.RunWorkerAsync();
           }
       }

       #endregion
   }