What Is the Epoll Interface?

Epoll is a Linux event-notification interface that lets a program register many file descriptors and then wait to learn which of them are ready for input or output. Unlike older approaches, its cost does not grow with the total number of descriptors watched. It is the basis for high-concurrency network servers on Linux.

Why it matters

Epoll is why event-driven servers can handle thousands of connections in one process, which underlies many tools CI depends on. Understanding it clarifies how non-blocking IO scales without a thread per connection.

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