I/O Multiplexing (select vs. poll vs. epoll/kqueue)

4 days ago

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I/O multiplexing processes multiple input/output events from a single event loop using system calls like poll and select.
kqueue (MacOS) and epoll (Linux) are scalable I/O event notification mechanisms designed for high concurrency scenarios like web servers.
select has performance issues with O(n) runtime and can crash processes when handling file descriptors beyond FD_SETSIZE (1024).
poll, introduced in 1986, improved upon select by removing the 1024 fd limit and offering more event types, but still operates in O(n) time.
kqueue, introduced in 2000, is a scalable event notification interface that efficiently manages events using kevent structures and system calls.
The kevent structure identifies events with an <ident, filter> pair and uses flags to manage event registration and behavior.
The kevent system call allows adding, modifying, or deleting events and waiting for events to occur.
An event loop with kqueue involves creating a queue, registering events, and handling them as they occur in an infinite loop.

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