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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"> | |
4 | ||
5 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2015 Lennart Poettering | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="sd-event" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
27 | ||
28 | <refentryinfo> | |
29 | <title>sd-event</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Lennart</firstname> | |
36 | <surname>Poettering</surname> | |
37 | <email>lennart@poettering.net</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd-event</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd-event</refname> | |
49 | <refpurpose>A generic event loop implementation</refpurpose> | |
50 | </refnamediv> | |
51 | ||
52 | <refsynopsisdiv> | |
53 | <funcsynopsis> | |
54 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
55 | </funcsynopsis> | |
56 | ||
57 | <cmdsynopsis> | |
58 | <command>pkg-config --cflags --libs libsystemd</command> | |
59 | </cmdsynopsis> | |
60 | ||
61 | </refsynopsisdiv> | |
62 | ||
63 | <refsect1> | |
64 | <title>Description</title> | |
65 | ||
66 | <para><filename>sd-event.h</filename> provides a generic event | |
67 | loop implementation, based on Linux <citerefentry | |
68 | project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>. | |
69 | </para> | |
70 | ||
71 | <para>See | |
72 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
73 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
74 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
75 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
76 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
77 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
78 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
79 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
80 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
81 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
82 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
83 | <citerefentry><refentrytitle>sd_event_source_get_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
84 | <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
85 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
86 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
87 | <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
88 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
89 | <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
90 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
91 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
92 | for more information about the functions available.</para> | |
93 | ||
94 | <para>The event loop design is targeted on running a separate | |
95 | instance of the event loop in each thread; it has no concept of | |
96 | distributing events from a single event loop instance onto | |
97 | multiple worker threads. Dispatching events is strictly ordered | |
98 | and subject to configurable priorities. In each event loop | |
99 | iteration a single event source is dispatched. Each time an event | |
100 | source is dispatched the kernel is polled for new events, before | |
101 | the next event source is dispatched. The event loop is designed to | |
2dd67817 | 102 | honor priorities and provide fairness within each priority. It is |
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103 | not designed to provide optimal throughput, as this contradicts |
104 | these goals due the limitations of the underlying <citerefentry | |
105 | project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
106 | primitives.</para> | |
107 | ||
108 | <para>The event loop implementation provides the following features:</para> | |
109 | ||
110 | <orderedlist> | |
111 | <listitem><para>I/O event sources, based on <citerefentry | |
112 | project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>'s | |
113 | file descriptor watching, including edge triggered events (<constant>EPOLLET</constant>). See <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> | |
114 | ||
115 | <listitem><para>Timer event sources, based on <citerefentry | |
116 | project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
117 | supporting the <constant>CLOCK_MONOTONIC</constant>, | |
118 | <constant>CLOCK_REALTIME</constant>, | |
119 | <constant>CLOCK_BOOTIME</constant> clocks, as well as the | |
120 | <constant>CLOCK_REALTIME_ALARM</constant> and | |
121 | <constant>CLOCK_BOOTTIME_ALARM</constant> clocks that can resume | |
122 | the system from suspend. When creating timer events a required | |
123 | accuracy parameter may be specified which allows coalescing of | |
124 | timer events to minimize power consumption. See <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> | |
125 | ||
126 | <listitem><para>UNIX process signal events, based on | |
127 | <citerefentry | |
128 | project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
129 | including full support for real-time signals, and queued parameters. See <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> | |
130 | ||
131 | <listitem><para>Child process state change events, based on | |
132 | <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> | |
133 | ||
134 | <listitem><para>Static event sources, of three types: defer, | |
135 | post and exit, for invoking calls in each event loop, after | |
136 | other event sources or at event loop termination. See | |
137 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> | |
138 | ||
139 | <listitem><para>Event sources may be assigned a 64bit priority | |
140 | value, that controls the order in which event sources are | |
7f3fdb7f | 141 | dispatched if multiple are pending simultaneously. See |
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142 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> |
143 | ||
144 | <listitem><para>The event loop may automatically send watchdog | |
145 | notification messages to the service manager. See | |
146 | <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem> | |
147 | ||
148 | <listitem><para>The event loop may be integrated into foreign | |
149 | event loops, such as the GLib one. See | |
150 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
151 | for an example.</para></listitem> | |
152 | </orderedlist> | |
153 | ||
154 | </refsect1> | |
155 | ||
156 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
157 | ||
158 | <refsect1> | |
159 | <title>See Also</title> | |
160 | <para> | |
161 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
162 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
163 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
164 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
165 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
166 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
167 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
168 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
169 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
170 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
171 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
172 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
173 | <citerefentry><refentrytitle>sd_event_source_get_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
174 | <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
175 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
176 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
177 | <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
178 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
179 | <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
180 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
181 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
182 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
183 | <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
184 | <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
185 | <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
186 | </para> | |
187 | </refsect1> | |
188 | ||
189 | </refentry> |