libev

What it is

libev is a high-performance event loop library in C that provides asynchronous I/O, timers, signals, and child process handling. It is designed for efficiency and scalability in networked and event-driven applications.

libev allows you to register watchers for I/O events, timers, signals, and child processes. The library invokes callback functions when events occur, making it suitable for scalable network servers and asynchronous applications.

Installation

sudo apt install libev-dev

Getting started

The smallest useful thing you can do with it, and what each part means.

Simple timer watcher

c

1234567891011121314151617#include <ev.h>
#include <stdio.h>

static void timeout_cb(EV_P_ ev_timer *w, int revents) {
    printf("Timer fired!\n");
}

int main() {
    struct ev_loop *loop = EV_DEFAULT;
    ev_timer timer_watcher;

    ev_timer_init(&timer_watcher, timeout_cb, 1.0, 0.0);
    ev_timer_start(loop, &timer_watcher);

    ev_run(loop, 0);
    return 0;
}

Creates a one-shot timer that fires after 1 second using libev.

I/O watcher example

c

// Monitor a file descriptor for readability using ev_io watcher and a callback function.

Advanced usage

Where the library earns its place over a simpler alternative.

Signal handling

c

// Use ev_signal watcher to handle signals like SIGINT and perform graceful shutdowns.

Child process monitoring

c

// Use ev_child watcher to detect when a child process exits and handle it asynchronously.

Combining multiple watchers

c

// Use ev_loop with timers, I/O, and signals together for complex event-driven programs.

Errors and fixes

The failures you are most likely to hit, and what actually resolves them.

ev_run returns unexpectedly: Ensure all watchers are initialized and started correctly; check for unhandled exceptions in callbacks.
Segmentation fault in callback: Verify that watcher pointers and user data are valid and properly allocated.

Best practices

Always use the default event loop unless multiple loops are required.
Avoid blocking calls in callbacks to maintain responsiveness.
Use proper initialization and start/stop watchers correctly.
Free resources and watchers when no longer needed.
Combine I/O, timer, and signal watchers efficiently to scale network applications.

Background

Why it exists, and what it was reacting to.

libev was created by Marc Lehmann as a portable and efficient alternative to other event libraries like libevent. It abstracts platform-specific event notification mechanisms (epoll, kqueue, select) and provides a consistent API for building fast asynchronous programs.

Related libraries

Others in Messaging & Streaming for C.

libwebsockets

libevent