4.8 KiB
libuEv | Simple event loop for Linux
Introduction
libuEv is a simple event loop in the style of the more established libevent, libev and the venerable Xt(3) event loop. The u (micro) in the name refers to both the small feature set and the small size overhead impact of the library.
Experienced developers may appreciate that libuEv is built on top of modern Linux APIs: epoll, timerfd and signalfd. Note however, a certain amount of care is needed when dealing with APIs that employ signalfd. For details, see this article at lwn.net.
“Event driven software improves concurrency” -- Dave Zarzycki, Apple
Documentation
The API documentation is available as separate README in the src/
directory.
Build & Install
The library is built for and developed on GNU/Linux systems, patches to support *BSD and its kqueue interface are most welcome.
libuEv use the GNU configure and build system. To try out the bundled
examples, use the --enable-examples switch to the configure script.
$ ./configure
$ make -j5
$ make test
$ sudo make install-strip
$ sudo ldconfig
The resulting .so file is ~14 kiB (make install-strip).
Background
“Why an event loop, why not use threads?”
With the advent of light-weight processes (threads) programmers these days have a golden hammer they often swing without consideration. Event loops and non-blocking I/O is often a far easier approach, as well as less error prone.
The purpose of many applications is, with a little logic sprinkled on top, to act on network packets entering an interface, timeouts expiring, mouse clicks, or other types of events. Such applications are often very well suited to use an event loop.
Applications that need to churn massively parallel algorithms are more suitable for running multiple (independent) threads on several CPU cores. However, threaded applications must deal with the side effects of concurrency, like race conditions, deadlocks, live locks, etc. Writing error free threaded applications is hard, debugging them can be even harder.
Sometimes the combination of multiple threads and an event loop per thread can be the best approach, but each application of course needs to be broken down individually to find the most optimal approach. Do keep in mind, however, that not all systems your application will run on have multiple CPU cores -- some small embedded systems still use a single CPU core, even though they run Linux, with multiple threads a program may actually run slower! Always profile your program, and if possible, test it on different architectures.
Origin & References
libuEv was originally based on LibUEvent by Flemming Madsen but has been completely rewritten with a much clearer API. Now more similar to the famous libev by Mark Lehmann. Another small event library used for inspiration is the very small Picoev by Oku Kazuho.
libuEv is developed and maintained by Joachim Nilsson.