Call this function to begin a busy state.
virtual void BeginBusyState( );
The BeginBusyState and EndBusyState calls increment and decrement, respectively, a counter that determines whether the application is busy. For example, two calls to BeginBusyState and one call to EndBusyState still result in a busy state. To cancel a busy state it is necessary to call EndBusyState the same number of times BeginBusyState has been called.
By default, the framework enters the busy state during idle processing, which is performed by CWinApp::OnIdle. While the application is handling ON_COMMANDUPDATEUI notifications, incoming calls are handled later, after idle processing is complete.