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@@ -3,9 +3,6 @@ libuEv | Simple event loop for Linux
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[![Travis Status][]][Travis] [![Coverity Status][]][Coverity Scan]
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Table of Contents
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-----------------
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* [Introduction](#introduction)
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* [API](#api)
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* [Create an Event Context](#create-an-event-context)
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@@ -15,50 +12,22 @@ Table of Contents
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* [Using -luev](#using--luev)
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* [Joystick Example](#joystick-example)
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* [Build & Install](#build--install)
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* [Background](#background)
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* [Origin & References](#origin--references)
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Introduction
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------------
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> “Why an event loop, why not use threads?”
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With the advent of light-weight processes (threads) programmers these
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days have a [golden hammer](http://c2.com/cgi/wiki?GoldenHammer) they
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often swing without consideration. Event loops and non-blocking I/O is
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often a far easier approach, as well as less error prone.
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The purpose of many applications is, with a little logic sprinkled on
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top, to act on network packets entering an interface, timeouts expiring,
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mouse clicks, or other types of events. Such applications are often
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very well suited to use an event loop.
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Applications that need to churn massively parallel algorithms are more
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suitable for running multiple (independent) threads on several CPU
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cores. However, threaded applications must deal with the side effects
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of concurrency, like race conditions, deadlocks, live locks, etc.
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Writing error free threaded applications is hard, debugging them can be
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even harder.
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Sometimes the combination of multiple threads *and* an event loop per
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thread can be the best approach, but each application of course needs to
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be broken down individually to find the most optimal approach. Do keep
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in mind, however, that not all systems your application will run on have
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multiple CPU cores -- some small embedded systems still use a single CPU
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core, even though they run Linux, with multiple threads a program may
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actually run slower! Always profile your program, and if possible, test
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it on different architectures.
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[libuEv][] is a simple event loop in the style of the more established
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[libevent][1], [libev][2] and the venerable [Xt(3)][3] event loop. The
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*u* (micro) in the name refers to both the small feature set and the
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small size overhead impact of the library. The primary target of
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[libuEv][] is a modern Linux system.
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small size overhead impact of the library.
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Experienced developers may appreciate that [libuEv][] is built on top of
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modern Linux APIs: epoll, timerfd and signalfd. Note, a certain amount
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of care is needed when dealing with APIs that employ signalfd. For
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details, see [this article][4] at [lwn.net](http://lwn.net).
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modern Linux APIs: epoll, timerfd and signalfd. Note however, a certain
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amount of care is needed when dealing with APIs that employ signalfd.
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For details, see [this article][4] at [lwn.net](http://lwn.net).
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> “Event driven software improves concurrency” -- [Dave Zarzycki, Apple][]
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@@ -306,7 +275,7 @@ Build & Install
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---------------
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The library is built for and developed on GNU/Linux systems, patches to
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support *BSD and its kqueue interface are most welcome.
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support *BSD and its [kqueue][] interface are most welcome.
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libuEv use the GNU configure and build system. To try out the bundled
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examples, use the `--enable-examples` switch to the `configure` script.
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@@ -319,6 +288,38 @@ examples, use the `--enable-examples` switch to the `configure` script.
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The resulting .so file is ~14 kiB (<kbd>make install-strip</kbd>).
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Background
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----------
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> “Why an event loop, why not use threads?”
|
|
|
|
|
|
|
|
|
|
With the advent of light-weight processes (threads) programmers these
|
|
|
|
|
days have a [golden hammer](http://c2.com/cgi/wiki?GoldenHammer) 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
|
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|
|
|
core, even though they run Linux, with multiple threads a program may
|
|
|
|
|
actually run slower! Always profile your program, and if possible, test
|
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|
|
|
it on different architectures.
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Origin & References
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-------------------
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@@ -344,6 +345,7 @@ event library used for inspiration is the very small [Picoev][9] by
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[Coverity Scan]: https://scan.coverity.com/projects/3846
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[Coverity Status]: https://scan.coverity.com/projects/3846/badge.svg
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[LibuEv]: https://github.com/troglobit/libuev
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[kqueue]: https://github.com/mheily/libkqueue
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[Oku Kazuho]: https://github.com/kazuho
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[Mark Lehmann]: http://software.schmorp.de
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[Joachim Nilsson]: http://troglobit.com
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