1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 This file is part of elogind.
7 SPDX-License-Identifier: LGPL-2.1+
10 Copyright 2015 Lennart Poettering
13 <refentry id="sd-event" xmlns:xi="http://www.w3.org/2001/XInclude">
16 <title>sd-event</title>
17 <productname>elogind</productname>
21 <contrib>Developer</contrib>
22 <firstname>Lennart</firstname>
23 <surname>Poettering</surname>
24 <email>lennart@poettering.net</email>
30 <refentrytitle>sd-event</refentrytitle>
31 <manvolnum>3</manvolnum>
35 <refname>sd-event</refname>
36 <refpurpose>A generic event loop implementation</refpurpose>
41 <funcsynopsisinfo>#include <elogind/sd-event.h></funcsynopsisinfo>
45 <command>pkg-config --cflags --libs libelogind</command>
51 <title>Description</title>
53 <para><filename>sd-event.h</filename> provides a generic event
54 loop implementation, based on Linux <citerefentry
55 project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
59 <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
60 <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
61 <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
62 <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
63 <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
64 <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
65 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
66 <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
67 <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
68 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
69 <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
70 <citerefentry><refentrytitle>sd_event_source_get_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
71 <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
72 <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
73 <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
74 <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
75 <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
76 <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
77 <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
78 <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>
79 for more information about the functions available.</para>
81 <para>The event loop design is targeted on running a separate
82 instance of the event loop in each thread; it has no concept of
83 distributing events from a single event loop instance onto
84 multiple worker threads. Dispatching events is strictly ordered
85 and subject to configurable priorities. In each event loop
86 iteration a single event source is dispatched. Each time an event
87 source is dispatched the kernel is polled for new events, before
88 the next event source is dispatched. The event loop is designed to
89 honor priorities and provide fairness within each priority. It is
90 not designed to provide optimal throughput, as this contradicts
91 these goals due the limitations of the underlying <citerefentry
92 project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
95 <para>The event loop implementation provides the following features:</para>
98 <listitem><para>I/O event sources, based on <citerefentry
99 project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>'s
100 file descriptor watching, including edge triggered events (<constant>EPOLLET</constant>). See <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
102 <listitem><para>Timer event sources, based on <citerefentry
103 project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
104 supporting the <constant>CLOCK_MONOTONIC</constant>,
105 <constant>CLOCK_REALTIME</constant>,
106 <constant>CLOCK_BOOTIME</constant> clocks, as well as the
107 <constant>CLOCK_REALTIME_ALARM</constant> and
108 <constant>CLOCK_BOOTTIME_ALARM</constant> clocks that can resume
109 the system from suspend. When creating timer events a required
110 accuracy parameter may be specified which allows coalescing of
111 timer events to minimize power consumption. See <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
113 <listitem><para>UNIX process signal events, based on
115 project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
116 including full support for real-time signals, and queued parameters. See <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
118 <listitem><para>Child process state change events, based on
119 <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>. See <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
121 <listitem><para>Static event sources, of three types: defer,
122 post and exit, for invoking calls in each event loop, after
123 other event sources or at event loop termination. See
124 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
126 <listitem><para>Event sources may be assigned a 64bit priority
127 value, that controls the order in which event sources are
128 dispatched if multiple are pending simultaneously. See
129 <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
131 <listitem><para>The event loop may automatically send watchdog
132 notification messages to the service manager. See
133 <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
135 <listitem><para>The event loop may be integrated into foreign
136 event loops, such as the GLib one. See
137 <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>
138 for an example.</para></listitem>
143 <xi:include href="libelogind-pkgconfig.xml" />
146 <title>See Also</title>
148 <!-- 0 /// elogind is in section 8
149 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
151 <citerefentry><refentrytitle>elogind</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
153 <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
154 <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
155 <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
156 <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
157 <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
158 <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
159 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
160 <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
161 <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
162 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
163 <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
164 <citerefentry><refentrytitle>sd_event_source_get_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
165 <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
166 <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
167 <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
168 <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
169 <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
170 <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
171 <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
172 <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
173 <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
174 <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
175 <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
176 <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>