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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 | <!-- | |
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6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2015 Zbigniew Jędrzejewski-Szmek | |
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 | ||
dc83f27a | 26 | <refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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27 | |
28 | <refentryinfo> | |
29 | <title>sd_event_wait</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Tom</firstname> | |
36 | <surname>Gundersen</surname> | |
37 | <email>teg@jklm.no</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd_event_wait</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd_event_wait</refname> | |
49 | <refname>sd_event_prepare</refname> | |
50 | <refname>sd_event_dispatch</refname> | |
dc83f27a | 51 | <refname>sd_event_get_state</refname> |
60a3b1e1 | 52 | <refname>sd_event_get_iteration</refname> |
dc83f27a LP |
53 | <refname>SD_EVENT_INITIAL</refname> |
54 | <refname>SD_EVENT_PREPARING</refname> | |
55 | <refname>SD_EVENT_ARMED</refname> | |
56 | <refname>SD_EVENT_PENDING</refname> | |
57 | <refname>SD_EVENT_RUNNING</refname> | |
58 | <refname>SD_EVENT_EXITING</refname> | |
59 | <refname>SD_EVENT_FINISHED</refname> | |
60 | ||
61 | <refpurpose>Low-level event loop operations</refpurpose> | |
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62 | </refnamediv> |
63 | ||
64 | <refsynopsisdiv> | |
65 | <funcsynopsis> | |
66 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
67 | ||
dc83f27a LP |
68 | <funcsynopsisinfo><token>enum</token> { |
69 | <constant>SD_EVENT_INITIAL</constant>, | |
70 | <constant>SD_EVENT_PREPARING</constant>, | |
71 | <constant>SD_EVENT_ARMED</constant>, | |
72 | <constant>SD_EVENT_PENDING</constant>, | |
73 | <constant>SD_EVENT_RUNNING</constant>, | |
74 | <constant>SD_EVENT_EXITING</constant>, | |
75 | <constant>SD_EVENT_FINISHED</constant>, | |
76 | };</funcsynopsisinfo> | |
77 | ||
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78 | <funcprototype> |
79 | <funcdef>int <function>sd_event_prepare</function></funcdef> | |
80 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
81 | </funcprototype> | |
82 | ||
83 | <funcprototype> | |
84 | <funcdef>int <function>sd_event_wait</function></funcdef> | |
85 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
dc83f27a | 86 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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87 | </funcprototype> |
88 | ||
89 | <funcprototype> | |
90 | <funcdef>int <function>sd_event_dispatch</function></funcdef> | |
91 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
92 | </funcprototype> | |
93 | ||
dc83f27a LP |
94 | <funcprototype> |
95 | <funcdef>int <function>sd_event_get_state</function></funcdef> | |
96 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
97 | </funcprototype> | |
98 | ||
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99 | <funcprototype> |
100 | <funcdef>int <function>sd_event_get_iteration</function></funcdef> | |
101 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
102 | <paramdef>uint64_t *<parameter>ret</parameter></paramdef> | |
103 | </funcprototype> | |
104 | ||
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105 | </funcsynopsis> |
106 | </refsynopsisdiv> | |
107 | ||
108 | <refsect1> | |
109 | <title>Description</title> | |
110 | ||
dc83f27a LP |
111 | <para>The low-level <function>sd_event_prepare()</function>, |
112 | <function>sd_event_wait()</function> and | |
113 | <function>sd_event_dispatch()</function> functions may be used to | |
114 | execute specific phases of an event loop. See | |
115 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
116 | and | |
117 | <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
118 | for higher-level functions that execute individual but complete | |
7f3fdb7f | 119 | iterations of an event loop or run it continuously.</para> |
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120 | |
121 | <para><function>sd_event_prepare()</function> checks for pending | |
42f1ab50 | 122 | events and arms necessary timers. If any events are ready to be |
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123 | processed ("pending"), it returns a positive, non-zero value, and the caller |
124 | should process these events with | |
125 | <function>sd_event_dispatch()</function>.</para> | |
126 | ||
127 | <para><function>sd_event_dispatch()</function> dispatches the | |
128 | highest priority event source that has a pending event. On | |
129 | success, <function>sd_event_dispatch()</function> returns either | |
130 | zero, which indicates that no further event sources may be | |
131 | dispatched and exiting of the event loop was requested via | |
132 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>; | |
133 | or a positive non-zero value, which means that an event source was | |
134 | dispatched and the loop returned to its initial state, and the | |
135 | caller should initiate the next event loop iteration by invoking | |
136 | <function>sd_event_prepare()</function> again.</para> | |
137 | ||
138 | <para>In case <function>sd_event_prepare()</function> returned | |
139 | zero, <function>sd_event_wait()</function> should be called to | |
140 | wait for further events or a timeout. If any events are ready to | |
141 | be processed, it returns a positive, non-zero value, and the | |
142 | events should be dispatched with | |
143 | <function>sd_event_dispatch()</function>. Otherwise, the event | |
144 | loop returned to its initial state and the next event loop | |
145 | iteration should be initiated by invoking | |
146 | <function>sd_event_prepare()</function> again.</para> | |
147 | ||
148 | <para><function>sd_event_get_state()</function> may be used to | |
149 | determine the state the event loop is currently in. It returns one | |
150 | of the states described below.</para> | |
151 | ||
60a3b1e1 LP |
152 | <para><function>sd_event_get_iteration()</function> may be used to determine the current iteration of the event |
153 | loop. It returns an unsigned 64bit integer containing a counter that increases monotonically with each iteration of | |
154 | the event loop, starting with 0. The counter is increased at the time of the | |
155 | <function>sd_event_prepare()</function> invocation.</para> | |
156 | ||
157 | <para>All five functions take, as the first argument, the event loop object <parameter>event</parameter> that has | |
158 | been created with <function>sd_event_new()</function>. The timeout for <function>sd_event_wait()</function> is | |
159 | specified in <parameter>usec</parameter> in microseconds. <constant>(uint64_t) -1</constant> may be used to | |
160 | specify an infinite timeout.</para> | |
dc83f27a LP |
161 | </refsect1> |
162 | ||
163 | <refsect1> | |
164 | <title>State Machine</title> | |
165 | ||
166 | <para>The event loop knows the following states, that may be | |
167 | queried with <function>sd_event_get_state()</function>.</para> | |
42f1ab50 | 168 | |
dc83f27a LP |
169 | <variablelist> |
170 | <varlistentry> | |
171 | <term><constant>SD_EVENT_INITIAL</constant></term> | |
172 | ||
173 | <listitem><para>The initial state the event loop is in, | |
174 | before each event loop iteration. Use | |
175 | <function>sd_event_prepare()</function> to transition the | |
176 | event loop into the <constant>SD_EVENT_ARMED</constant> or | |
177 | <constant>SD_EVENT_PENDING</constant> states.</para></listitem> | |
178 | </varlistentry> | |
179 | ||
180 | <varlistentry> | |
181 | <term><constant>SD_EVENT_PREPARING</constant></term> | |
182 | ||
183 | <listitem><para>An event source is currently being prepared, | |
7f3fdb7f | 184 | i.e. the preparation handler is currently being executed, as |
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185 | set with |
186 | <citerefentry><refentrytitle>sd_event_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This | |
187 | state is only seen in the event source preparation handler | |
188 | that is invoked from the | |
189 | <function>sd_event_prepare()</function> call and is | |
190 | immediately followed by <constant>SD_EVENT_ARMED</constant> or | |
191 | <constant>SD_EVENT_PENDING</constant>.</para></listitem> | |
192 | </varlistentry> | |
193 | ||
194 | <varlistentry> | |
195 | <term><constant>SD_EVENT_ARMED</constant></term> | |
196 | ||
197 | <listitem><para><function>sd_event_prepare()</function> has | |
198 | been called and no event sources were ready to be | |
199 | dispatched. Use <function>sd_event_wait()</function> to wait | |
200 | for new events, and transition into | |
201 | <constant>SD_EVENT_PENDING</constant> or back into | |
202 | <constant>SD_EVENT_INITIAL</constant>.</para></listitem> | |
203 | </varlistentry> | |
204 | ||
205 | <varlistentry> | |
206 | <term><constant>SD_EVENT_PENDING</constant></term> | |
207 | ||
208 | <listitem><para><function>sd_event_prepare()</function> or | |
209 | <function>sd_event_wait()</function> have been called and | |
210 | there were event sources with events pending. Use | |
211 | <function>sd_event_dispatch()</function> to dispatch the | |
212 | highest priority event source and transition back to | |
213 | <constant>SD_EVENT_INITIAL</constant>, or | |
214 | <constant>SD_EVENT_FINISHED</constant>.</para></listitem> | |
215 | </varlistentry> | |
216 | ||
217 | <varlistentry> | |
218 | <term><constant>SD_EVENT_RUNNING</constant></term> | |
219 | ||
220 | <listitem><para>A regular event source is currently being | |
221 | dispatched. This state is only seen in the event source | |
222 | handler that is invoked from the | |
223 | <function>sd_event_dispatch()</function> call, and is | |
224 | immediately followed by <constant>SD_EVENT_INITIAL</constant> | |
225 | or <constant>SD_EVENT_FINISHED</constant> as soon the event | |
226 | source handler returns. Note that during dispatching of exit | |
227 | event sources the <constant>SD_EVENT_EXITING</constant> state | |
228 | is seen instead.</para></listitem> | |
229 | </varlistentry> | |
230 | ||
231 | <varlistentry> | |
232 | <term><constant>SD_EVENT_EXITING</constant></term> | |
233 | ||
234 | <listitem><para>Similar to | |
235 | <constant>SD_EVENT_RUNNING</constant> but is the state in | |
236 | effect while dispatching exit event sources. It is followed by | |
237 | <constant>SD_EVENT_INITIAL</constant> or | |
238 | <constant>SD_EVENT_FINISHED</constant> as soon as the event | |
239 | handler returns.</para></listitem> | |
240 | </varlistentry> | |
241 | ||
242 | <varlistentry> | |
243 | <term><constant>SD_EVENT_FINISHED</constant></term> | |
244 | ||
245 | <listitem><para>The event loop has exited. All exit event | |
246 | sources have run. If the event loop is in this state it serves | |
247 | no purpose anymore, and should be freed.</para></listitem> | |
248 | </varlistentry> | |
249 | ||
250 | </variablelist> | |
251 | ||
252 | <para>A simplified flow chart of the states and the calls to | |
253 | transition between them is shown below. Note that | |
254 | <constant>SD_EVENT_PREPARING</constant>, | |
255 | <constant>SD_EVENT_RUNNING</constant> and | |
256 | <constant>SD_EVENT_EXITING</constant> are not shown here.</para> | |
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257 | |
258 | <programlisting> | |
dc83f27a LP |
259 | INITIAL -<---<---<---<---<---<---<---<---<---<---<---<---\ |
260 | | | | |
261 | | ^ | |
262 | | | | |
263 | v ret == 0 | | |
264 | sd_event_prepare() >--->--->--->--->- ARMED | | |
265 | | | ^ | |
266 | | ret > 0 | | | |
267 | | | | | |
268 | v v ret == 0 | | |
269 | PENDING <---<---<---<---<---< sd_event_wait() >--->--->--+ | |
270 | | ret > 0 ^ | |
271 | | | | |
272 | | | | |
273 | v | | |
274 | sd_event_dispatch() >--->--->--->--->--->--->--->--->--->--->/ | |
275 | | ret > 0 | |
276 | | ret == 0 | |
277 | | | |
278 | v | |
279 | FINISHED | |
42f1ab50 | 280 | </programlisting> |
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281 | </refsect1> |
282 | ||
283 | <refsect1> | |
284 | <title>Return Value</title> | |
285 | ||
286 | <para>On success, these functions return 0 or a positive integer. | |
287 | On failure, they return a negative errno-style error code. In case | |
dc83f27a LP |
288 | of <function>sd_event_prepare()</function> and |
289 | <function>sd_event_wait()</function>, a positive, non-zero return | |
290 | code indicates that events are ready to be processed and zero | |
291 | indicates that no events are ready. In case of | |
292 | <function>sd_event_dispatch()</function>, a positive, non-zero | |
293 | return code indicates that the event loop returned to its initial | |
294 | state and zero indicates the event loop has | |
295 | exited. <function>sd_event_get_state()</function> returns a | |
296 | positive or zero state on success.</para> | |
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297 | </refsect1> |
298 | ||
299 | <refsect1> | |
300 | <title>Errors</title> | |
301 | ||
302 | <para>Returned errors may indicate the following problems:</para> | |
303 | ||
304 | <variablelist> | |
305 | <varlistentry> | |
306 | <term><constant>-EINVAL</constant></term> | |
307 | ||
a8eaaee7 | 308 | <listitem><para>The <parameter>event</parameter> parameter is |
dc83f27a | 309 | invalid or <constant>NULL</constant>.</para></listitem> |
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310 | </varlistentry> |
311 | ||
312 | <varlistentry> | |
313 | <term><constant>-EBUSY</constant></term> | |
314 | ||
315 | <listitem><para>The event loop object is not in the right | |
316 | state.</para></listitem> | |
317 | </varlistentry> | |
318 | ||
319 | <varlistentry> | |
320 | <term><constant>-ESTALE</constant></term> | |
321 | ||
322 | <listitem><para>The event loop is already terminated.</para></listitem> | |
323 | ||
324 | </varlistentry> | |
325 | ||
326 | <varlistentry> | |
327 | <term><constant>-ECHILD</constant></term> | |
328 | ||
329 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
330 | ||
331 | </varlistentry> | |
332 | ||
333 | </variablelist> | |
334 | ||
b938cb90 | 335 | <para>Other errors are possible, too.</para> |
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336 | </refsect1> |
337 | ||
dc83f27a | 338 | <xi:include href="libsystemd-pkgconfig.xml" /> |
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339 | |
340 | <refsect1> | |
341 | <title>See Also</title> | |
342 | ||
343 | <para> | |
344 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
345 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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346 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
347 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
348 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
349 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
350 | <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
dc83f27a LP |
351 | <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
352 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
353 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
354 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
42f1ab50 ZJS |
355 | </para> |
356 | </refsect1> | |
357 | ||
358 | </refentry> |