libevent

Libevent is a powerful API that provides a mechanism to execute a callback function when specific events occur on file descriptors or timouts occur. It also supports callbacks due to signals or regular timeouts.

Designed for event-driven network servers, Libevent replaces the event loop with a simple application that needs only to call event_dispatch(). At that point, events can be added or removed dynamically without having to alter the event loop.

Libevent supports /dev/poll, kqueue(2), event ports, select(2), poll(2) and epoll(4), making it versatile and adaptable. The internal event mechanism is independent of the exposed event API, which means that a simple update of Libevent can provide new functionality without redesigning the application.

This portability extends to multi-threaded applications, making Libevent an excellent choice for developers working on a range of platforms. It is a cross-platform library and should compile on Mac OS X, Linux, BSD, Solaris and Windows.

In short, Libevent offers a scalable event notification mechanism that provides a seamless experience for developers without sacrificing versatility or functionality. It is an excellent choice for those looking to develop portable applications without having to compromise on performance.