computer science

Libevent

Libevent is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Libevent rather than just read about it. In short: libevent is a software library that provides asynchronous event notification. 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. libevent also supports callbacks triggered by signals and regular timeouts. libevent is meant to replace the event loop found in event-driven network servers.

Key takeaways

Libevent belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Libevent to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Libevent from memory before moving on to harder problems.

Reference excerpt

libevent is a software library that provides asynchronous event notification. 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. libevent also supports callbacks triggered by signals and regular timeouts. libevent is meant to replace the event loop found in event-driven network servers. An application can just call event_dispatch() and then add or remove events dynamically without having to change the event loop. Currently, libevent supports /dev/poll, kqueue(2), POSIX select(2), Windows IOCP, poll(2), epoll(7) and Solaris event ports. It also has experimental support for real-time signals. The exposed event API is uniform over all of the supported platforms. As a result, libevent allows for portable application development and provides "the most scalable event notification mechanism available on an operating system". Using callbacks on signals, libevent makes it possible to write "secure" signal handlers as none of the user supplied signal handling code runs in the signal's context. libevent was created by Niels Provos, and is maintained primarily by Azat Khuzhin. It is released under a BSD license.

Notable applications

Some of the notable applications that take advantage of libevent are:

Chromium: Google's open-source web browser memcached: a high-performance, distributed memory object caching system Transmission: a fast, easy, and free BitTorrent client NTP: the network time protocol that makes your clock right (uses libevent in SNTP) tmux: a terminal multiplexer Tor: an anonymous Internet communication system

Alternatives libev libuv FAM Boost Asio

Major version releases libevent 2.1 was released on April 3, 2012. libevent 2.0 was released on April 17, 2009. libevent 1.4 was released on November 11, 2007. libevent 1.3 was released on February 15, 2007. libevent 1.2 was released on October 15, 2006. libevent 1.1 was released on May 14, 2005.

References

External links

Libevent web page Libevent github repository Libevent 2.0 book Dan Kegel's "The C10K problem" web page A benchmark by the libev author comparing libevent with libev, a similar library

Worked examples

Example 1 — a first encounter with Libevent

Start with the simplest possible case. Write down what Libevent claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Libevent before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Libevent ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Libevent

In research: Libevent appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Libevent in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Libevent is common in secondary-school and first-year university syllabi. It links to neighbouring topics C (programming language) libraries, Events (computing), Free computer libraries, so understanding it makes those chapters shorter.
In everyday life: Look for Libevent outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Libevent in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Libevent means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Libevent out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Libevent in simple terms?

Why does Libevent matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Libevent?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Libevent.