libuv

libuv is a multi-platform library for asynchronous I/O. It was primarily developed for use by Node.js, but it's also used by Luvit, Julia, pyuv, and others.
It supports Windows IOCP, epoll, kqueue, and Solaris event ports. It also provides the event loop and callback-based asynchrony. The library is written in C and has bindings to various languages.

Features

1. Cross-Platform Abstraction: It hides different low-level OS notification systems—like epoll on Linux, kqueue on macOS, and IOCP on Windows—behind a single uniform API.
2. Event Loop: It manages an event loop that runs callbacks when tasks (like network requests or timers) finish, keeping applications fast and non-blocking.
3. Thread Pool: It provides an internal thread pool to handle operations that do not have native asynchronous support from the operating system, such as file system tasks.

Example

1. Create a Timer

$ sudo apt-get install libuv1-dev           Install libuv

#include <stdio.h>
#include <uv.h>

// This function runs when the timer finishes
void on_timer(uv_timer_t* handle) {
    printf("Timer finished!\n");
}

int main() {
    uv_loop_t *loop = uv_default_loop();

    uv_timer_t timer;
    uv_timer_init(loop, &timer);
    
    // Start the timer: call on_timer after 1000ms (1 second), do not repeat
    uv_timer_start(&timer, on_timer, 1000, 0);

    // Run the event loop
    uv_run(loop, UV_RUN_DEFAULT);

    // Clean up
    uv_loop_close(loop);
    return 0;
}