Polling limits the capabilities of the MVC paradigm. The use of processor time to test for incoming events is the primary shortcoming, especially in a multitasking environment. Polling becomes very difficult and inefficient in a multitasking environment because it limits the system to sequential processing of user input and eliminates the possibility for multiple input foci. In addition, polling code is typically littered with special case tests and exceptions. The thread of control becomes confusing because of multiple nested polling loops in the controllers. Secondly, there is considerable processing overhead involved in finding the active view and the correct context for an event.