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Software → Programming

Event Loop

A runtime mechanism that waits for events and dispatches callbacks or tasks without blocking the main execution flow.

Motivation

Event loop solves the problem of handling many waiting operations with a small number of threads.

Where it fits

Event Loop belongs to runtime systems and asynchronous programming.

Mental model

An event loop repeatedly picks ready events or callbacks and runs them without blocking on every I/O operation.

Common mistakes

Blocking the event loop with CPU-heavy work.
Assuming async code automatically runs in parallel.

Event Loop connects to asynchronous programming, non-blocking I/O, callback, promise, and concurrency.