libevent - an event notification library
  
 
The libevent API provides a mechanism to execute a callback function when a specific event occurs on a file descriptor or after a timeout has been reached. Furthermore, libevent also support callbacks due to signals or regular timeouts.

libevent is meant to replace the event loop found in event driven network servers. An application just needs to call event_dispatch() and then add or remove events dynamically without having to change the event loop.

Currently, libevent supports /dev/poll, kqueue(2), event ports, select(2), poll(2) and epoll(4). The internal event mechanism is completely independent of the exposed event API, and a simple update of libevent can provide new functionality without having to redesign the applications. As a result, Libevent allows for portable application development and provides the most scalable event notification mechanism available on an operating system. Libevent can also be used for multi-threaded applications; see Steven Grimm's explanation. Libevent should compile on Linux, *BSD, Mac OS X, Solaris and Windows.

More information about event notification mechanisms for network servers can be found on Dan Kegel's "The C10K problem" web page. Another library that abstracts asynchronous event notification is liboop.

A mailing list for libevent is now available. Libevent is maintained by Nick Mathewson and Niels Provos.

 
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Documentation and Support

Documentation: Libevent 1.4.3-stable
Sample Application: event-test.c.
Bug Tracking: Bugs Features
Mailing List: Info Blog

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Libevent has been released under a 3-clause BSD license. Information on public subversion access. 		     

Benchmark

Performance comparison using different event notification mechansims in Libevent. We declare interest in a large number of connections of which most are cold and only a few are active.
 
The benchmark measures how long it takes to serve one active connection and exposes scalability issues of traditional interfaces like select or poll.   The benchmark measures how long it takes to serve one hundred active connections that chain writes to new connections until thousand writes and reads have happened. It exercises the event loop several times.

  

Programs using libevent

The usefulness of libevent API is demonstrated by the following applications:
  • Vomit - Voice Over Misconfigured Internet Telephones
  • Crawl - A Small and Efficient HTTP Crawler
  • Libio - an input/output abstraction library
  • Honeyd - a virtual honeynet daemon - can be used to fight Internet worms.
  • Fragroute - an IDS testing tool
  • Nylon - nested proxy server
  • Disconcert - a Distributed Computing Framework for Loosely-Coupled Workstations.
  • PLB - pure load balancer: a free high-performance load balancer for Unix.
  • Trickle - a lightweight userspace bandwidth shaper.
  • Memcached - a high-performance, distributed memory object caching system.
  • watchcatd - software watchdog designed to take actions not as drastic as the usual solutions, which reset the machine.
  • ScanSSH - a fast SSH server and open proxy scanner.
  • Nttlscan - a network topology scanner for Honeyd.
  • NetChat - a combination of netcat and ppp's chat.
  • Io - a small programming language; uses libevent for network communication.
  • Tor - an anonymous Internet communication system.
  • Systrace - a system call sandbox.
  • SpyBye - detect malware on web pages.
  • GreenSQL - an SQL database firewall.
  • dnsscan - a fast scanner for identifying open recursive dns resolvers
  
Niels Provos
Last modified: Wed Apr 7 23:19:27 EDT 2004 		  You can keep me happy while hacking by reducing my Wishlists: Books, Music
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NB: configure magic as always provided by Dug Song, though I am learning.