What an event loop is
An event loop is a programming construct that continuously waits for events to occur and then dispatches each one to the appropriate code to handle it. Rather than running straight through a fixed set of steps, a program built around an event loop sits ready, responding to things as they happen - a click, a message arriving, a timer going off. The loop is the central mechanism that keeps the program responsive to this stream of events.
Why event loops exist
Many programs do not follow a simple start-to-finish path; instead, they must react to events that can happen at unpredictable times. Interactive applications, for example, need to respond whenever the user does something. The event loop provides a clean way to handle this: the program waits for the next event and deals with it, then waits again. This event-driven style fits naturally with software that must stay responsive to outside input.
How an event loop works
At its core, an event loop repeatedly does a simple cycle: it checks whether any events have occurred, and if so, it takes the next one and runs the code responsible for handling it. Once that handler finishes, the loop goes back to checking for more events. Events that arrive while the program is busy typically wait their turn in a queue. This steady loop of waiting, taking an event, and handling it is what gives the construct its name.
Handling events one at a time
A typical event loop processes events one at a time, finishing one before moving to the next. This keeps things orderly, but it means each handler should do its work and return promptly, so the loop can get back to serving other events. If a single handler takes too long, the program can feel unresponsive because the loop is stuck and cannot handle anything else. Keeping handlers short is therefore important in event-driven programs.
Where event loops are used
Event loops are at the heart of many kinds of software. Applications with user interfaces use them to respond to interactions. Programs that handle many incoming requests use them to react as each arrives. The event loop is also central to asynchronous programming, where a program starts tasks and responds to their results as they come in. Wherever software must react to a flow of events, the event loop is a common and powerful pattern.
Why it matters
The event loop is a fundamental pattern behind interactive and responsive software, from apps to servers. Understanding what an event loop is - a loop that waits for events and dispatches each to be handled - clarifies how programs react to input and manage many things happening over time. For anyone interested in how responsive and asynchronous software works, the event loop is a key concept.
Related on Skillo
See also: What is a callback function? Explained, Process vs thread: the difference explained.
Sources
Published date reflects the original event date (2023-05-30). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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