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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" | |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2015 Zbigniew Jędrzejewski-Szmek | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
48f69d8f | 24 | <refentry id="sd_event_wait"> |
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25 | |
26 | <refentryinfo> | |
27 | <title>sd_event_wait</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Tom</firstname> | |
34 | <surname>Gundersen</surname> | |
35 | <email>teg@jklm.no</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>sd_event_wait</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_event_wait</refname> | |
47 | <refname>sd_event_prepare</refname> | |
48 | <refname>sd_event_dispatch</refname> | |
49 | ||
50 | <refpurpose>Run parts of libsystemd event loop</refpurpose> | |
51 | </refnamediv> | |
52 | ||
53 | <refsynopsisdiv> | |
54 | <funcsynopsis> | |
55 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>int <function>sd_event_prepare</function></funcdef> | |
59 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
60 | </funcprototype> | |
61 | ||
62 | <funcprototype> | |
63 | <funcdef>int <function>sd_event_wait</function></funcdef> | |
64 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
65 | <paramdef>uint64_t <parameter>timeout</parameter></paramdef> | |
66 | </funcprototype> | |
67 | ||
68 | <funcprototype> | |
69 | <funcdef>int <function>sd_event_dispatch</function></funcdef> | |
70 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
71 | </funcprototype> | |
72 | ||
73 | </funcsynopsis> | |
74 | </refsynopsisdiv> | |
75 | ||
76 | <refsect1> | |
77 | <title>Description</title> | |
78 | ||
79 | <para>Functions described here form parts of an event loop.</para> | |
80 | ||
81 | <para><function>sd_event_prepare</function> checks for pending | |
82 | events and arms necessary timers. If any events are ready to be | |
83 | processed, it returns a positive value, and the events should be | |
84 | processed with <function>sd_event_dispatch</function>. | |
85 | <function>sd_event_dispatch</function> runs a handler for one of | |
86 | the events from the sources with the highest priority. On success, | |
87 | <function>sd_event_dispatch</function> returns either 0, which | |
88 | means that the loop is finished, or a positive value, which means | |
89 | that the loop is again in the initial state and | |
90 | <function>sd_event_prepare</function> should be called again. | |
91 | </para> | |
92 | ||
93 | <para>In case <function>sd_event_prepare</function> returned 0, | |
94 | <function>sd_event_wait</function> should be called to wait for | |
95 | events or a timeout. If any events are ready to be processed, it | |
96 | returns a positive value, and the events should be processed with | |
97 | <function>sd_event_dispatch</function>. Otherwise, the loop is | |
ff9b60f3 | 98 | back in the initial state and <function>sd_event_prepare</function> |
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99 | should be called again.</para> |
100 | ||
101 | <programlisting> | |
102 | ┌──────────┐ | |
103 | │ initial ├──←←←←←←←←←←←←←←←←←←←─┐ | |
104 | └───┬──────┘ ↑ | |
105 | │ ↑ | |
106 | sd_event_prepare ┌─────────┐ ↑ | |
107 | ├ 0 →→→→→→→──┤ armed │ ↑ | |
108 | 1 └───┬─────┘ ↑ | |
109 | ↓ │ ↑ | |
110 | ↓ sd_event_wait ↑ | |
111 | ├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘ | |
112 | ┌───┴──────┐ ↑ | |
113 | │ pending │ ↑ | |
114 | └───┬──────┘ ↑ | |
115 | │ ↑ | |
116 | sd_event_dispatch ↑ | |
117 | ↓ ↑ | |
118 | ├ 1 ──────────→→→→→→→─────────┘ | |
119 | 0 | |
120 | ↓ | |
121 | ┌───┴──────┐ | |
122 | │ finished │ | |
123 | └──────────┘ | |
124 | </programlisting> | |
125 | ||
126 | <para>All three functions as the first argument take the event | |
127 | loop object <parameter>event</parameter> that is created with with | |
128 | <function>sd_event_new</function>. The timeout for | |
129 | <function>sd_event_wait</function> is specified with | |
130 | <parameter>timeout</parameter> in milliseconds. | |
131 | <constant>(uint64_t) -1</constant> may be used to specify an | |
132 | infinite timeout.</para> | |
133 | </refsect1> | |
134 | ||
135 | <refsect1> | |
136 | <title>Return Value</title> | |
137 | ||
138 | <para>On success, these functions return 0 or a positive integer. | |
139 | On failure, they return a negative errno-style error code. In case | |
140 | of <function>sd_event_prepare</function> and | |
141 | <function>sd_event_wait</function> a positive value means that | |
142 | events are ready to be processed and 0 means that no events are | |
143 | ready. In case of <function>sd_event_dispatch</function> a | |
144 | positive value means that the loop is again in the initial state | |
145 | and 0 means the loop is finished. For any of those functions, a | |
146 | negative return value means the loop must be aborted.</para> | |
147 | </refsect1> | |
148 | ||
149 | <refsect1> | |
150 | <title>Errors</title> | |
151 | ||
152 | <para>Returned errors may indicate the following problems:</para> | |
153 | ||
154 | <variablelist> | |
155 | <varlistentry> | |
156 | <term><constant>-EINVAL</constant></term> | |
157 | ||
158 | <listitem><para>Parameter <parameter>event</parameter> is | |
159 | <constant>NULL</constant>.</para></listitem> | |
160 | </varlistentry> | |
161 | ||
162 | <varlistentry> | |
163 | <term><constant>-EBUSY</constant></term> | |
164 | ||
165 | <listitem><para>The event loop object is not in the right | |
166 | state.</para></listitem> | |
167 | </varlistentry> | |
168 | ||
169 | <varlistentry> | |
170 | <term><constant>-ESTALE</constant></term> | |
171 | ||
172 | <listitem><para>The event loop is already terminated.</para></listitem> | |
173 | ||
174 | </varlistentry> | |
175 | ||
176 | <varlistentry> | |
177 | <term><constant>-ECHILD</constant></term> | |
178 | ||
179 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
180 | ||
181 | </varlistentry> | |
182 | ||
183 | </variablelist> | |
184 | ||
185 | <para>Other errors are possible too.</para> | |
186 | </refsect1> | |
187 | ||
188 | <refsect1> | |
189 | <title>Notes</title> | |
190 | ||
191 | <para>Functions described here are available | |
192 | as a shared library, which can be compiled and linked to with the | |
193 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
194 | file.</para> | |
195 | </refsect1> | |
196 | ||
197 | <refsect1> | |
198 | <title>See Also</title> | |
199 | ||
200 | <para> | |
201 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
202 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
203 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
204 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
207 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
209 | <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
210 | </para> | |
211 | </refsect1> | |
212 | ||
213 | </refentry> |