MainThreadWorkItemDispatcher
MainThreadWorkItemDispatcher handles execution of WorkItems by
            directly executing them on the main thread. This is different
            from the SimpleWorkItemDispatcher where the work item is dispatched
            onto its own thread.
            
                
The level of parallelism supported
            
public MainThreadWorkItemDispatcher()
This method is not supported for
            this dispatcher. Using it will throw a
            NotSupportedException.
            
Dispatch a single work item for execution by
            executing it directly.
            
Start execution, dispatching the top level
            work into the main thread.