Description
Event driven systems are typically used when there is some asynchronous external activity that needs to be handled by a program. For example, a user who presses a button on their mouse. The outside activity causes the event (it fires), some outside hardware and or software will collect data about the event, and when the program signals that it is ready to accept an event, the event will be dispatched to the event handler software that will deal with it.
A program can choose to ignore events, and there may be libraries to dispatch an event to multiple handlers that may be programmed to listen for a particular event. The data associated with an event at a minimum specifies what type of event it is, but may include other information such as when it occurred, who or what caused it to occur, and extra data provided by the event source to the handler about how the event should be processed.
Events are typically used in user interfaces, where actions in the outside world (mouse clicks, window-resizing, keyboard presses, messages from other programs, etc.) are handled by the program as a series of events. Programs written for many windowing environments consist predominantly of event handlers.
Events can also be used at instruction set level, where they complement interrupts. Compared to interrupts, events are normally handled synchronously: the program explicitly waits for an event to be serviced (typically by calling an instruction that dispatches the next event), whereas an interrupt can demand service at any time.
Read more about this topic: Event (computing)
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