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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 | ||
dc83f27a | 24 | <refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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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> | |
dc83f27a | 49 | <refname>sd_event_get_state</refname> |
60a3b1e1 | 50 | <refname>sd_event_get_iteration</refname> |
dc83f27a LP |
51 | <refname>SD_EVENT_INITIAL</refname> |
52 | <refname>SD_EVENT_PREPARING</refname> | |
53 | <refname>SD_EVENT_ARMED</refname> | |
54 | <refname>SD_EVENT_PENDING</refname> | |
55 | <refname>SD_EVENT_RUNNING</refname> | |
56 | <refname>SD_EVENT_EXITING</refname> | |
57 | <refname>SD_EVENT_FINISHED</refname> | |
58 | ||
59 | <refpurpose>Low-level event loop operations</refpurpose> | |
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60 | </refnamediv> |
61 | ||
62 | <refsynopsisdiv> | |
63 | <funcsynopsis> | |
64 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
65 | ||
dc83f27a LP |
66 | <funcsynopsisinfo><token>enum</token> { |
67 | <constant>SD_EVENT_INITIAL</constant>, | |
68 | <constant>SD_EVENT_PREPARING</constant>, | |
69 | <constant>SD_EVENT_ARMED</constant>, | |
70 | <constant>SD_EVENT_PENDING</constant>, | |
71 | <constant>SD_EVENT_RUNNING</constant>, | |
72 | <constant>SD_EVENT_EXITING</constant>, | |
73 | <constant>SD_EVENT_FINISHED</constant>, | |
74 | };</funcsynopsisinfo> | |
75 | ||
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76 | <funcprototype> |
77 | <funcdef>int <function>sd_event_prepare</function></funcdef> | |
78 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
79 | </funcprototype> | |
80 | ||
81 | <funcprototype> | |
82 | <funcdef>int <function>sd_event_wait</function></funcdef> | |
83 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
dc83f27a | 84 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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85 | </funcprototype> |
86 | ||
87 | <funcprototype> | |
88 | <funcdef>int <function>sd_event_dispatch</function></funcdef> | |
89 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
90 | </funcprototype> | |
91 | ||
dc83f27a LP |
92 | <funcprototype> |
93 | <funcdef>int <function>sd_event_get_state</function></funcdef> | |
94 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
95 | </funcprototype> | |
96 | ||
60a3b1e1 LP |
97 | <funcprototype> |
98 | <funcdef>int <function>sd_event_get_iteration</function></funcdef> | |
99 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
100 | <paramdef>uint64_t *<parameter>ret</parameter></paramdef> | |
101 | </funcprototype> | |
102 | ||
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103 | </funcsynopsis> |
104 | </refsynopsisdiv> | |
105 | ||
106 | <refsect1> | |
107 | <title>Description</title> | |
108 | ||
dc83f27a LP |
109 | <para>The low-level <function>sd_event_prepare()</function>, |
110 | <function>sd_event_wait()</function> and | |
111 | <function>sd_event_dispatch()</function> functions may be used to | |
112 | execute specific phases of an event loop. See | |
113 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
114 | and | |
115 | <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
116 | for higher-level functions that execute individual but complete | |
7f3fdb7f | 117 | iterations of an event loop or run it continuously.</para> |
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118 | |
119 | <para><function>sd_event_prepare()</function> checks for pending | |
42f1ab50 | 120 | events and arms necessary timers. If any events are ready to be |
dc83f27a LP |
121 | processed ("pending"), it returns a positive, non-zero value, and the caller |
122 | should process these events with | |
123 | <function>sd_event_dispatch()</function>.</para> | |
124 | ||
125 | <para><function>sd_event_dispatch()</function> dispatches the | |
126 | highest priority event source that has a pending event. On | |
127 | success, <function>sd_event_dispatch()</function> returns either | |
128 | zero, which indicates that no further event sources may be | |
129 | dispatched and exiting of the event loop was requested via | |
130 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>; | |
131 | or a positive non-zero value, which means that an event source was | |
132 | dispatched and the loop returned to its initial state, and the | |
133 | caller should initiate the next event loop iteration by invoking | |
134 | <function>sd_event_prepare()</function> again.</para> | |
135 | ||
136 | <para>In case <function>sd_event_prepare()</function> returned | |
137 | zero, <function>sd_event_wait()</function> should be called to | |
138 | wait for further events or a timeout. If any events are ready to | |
139 | be processed, it returns a positive, non-zero value, and the | |
140 | events should be dispatched with | |
141 | <function>sd_event_dispatch()</function>. Otherwise, the event | |
142 | loop returned to its initial state and the next event loop | |
143 | iteration should be initiated by invoking | |
144 | <function>sd_event_prepare()</function> again.</para> | |
145 | ||
146 | <para><function>sd_event_get_state()</function> may be used to | |
147 | determine the state the event loop is currently in. It returns one | |
148 | of the states described below.</para> | |
149 | ||
60a3b1e1 LP |
150 | <para><function>sd_event_get_iteration()</function> may be used to determine the current iteration of the event |
151 | loop. It returns an unsigned 64bit integer containing a counter that increases monotonically with each iteration of | |
152 | the event loop, starting with 0. The counter is increased at the time of the | |
153 | <function>sd_event_prepare()</function> invocation.</para> | |
154 | ||
155 | <para>All five functions take, as the first argument, the event loop object <parameter>event</parameter> that has | |
156 | been created with <function>sd_event_new()</function>. The timeout for <function>sd_event_wait()</function> is | |
157 | specified in <parameter>usec</parameter> in microseconds. <constant>(uint64_t) -1</constant> may be used to | |
158 | specify an infinite timeout.</para> | |
dc83f27a LP |
159 | </refsect1> |
160 | ||
161 | <refsect1> | |
162 | <title>State Machine</title> | |
163 | ||
164 | <para>The event loop knows the following states, that may be | |
165 | queried with <function>sd_event_get_state()</function>.</para> | |
42f1ab50 | 166 | |
dc83f27a LP |
167 | <variablelist> |
168 | <varlistentry> | |
169 | <term><constant>SD_EVENT_INITIAL</constant></term> | |
170 | ||
171 | <listitem><para>The initial state the event loop is in, | |
172 | before each event loop iteration. Use | |
173 | <function>sd_event_prepare()</function> to transition the | |
174 | event loop into the <constant>SD_EVENT_ARMED</constant> or | |
175 | <constant>SD_EVENT_PENDING</constant> states.</para></listitem> | |
176 | </varlistentry> | |
177 | ||
178 | <varlistentry> | |
179 | <term><constant>SD_EVENT_PREPARING</constant></term> | |
180 | ||
181 | <listitem><para>An event source is currently being prepared, | |
7f3fdb7f | 182 | i.e. the preparation handler is currently being executed, as |
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183 | set with |
184 | <citerefentry><refentrytitle>sd_event_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This | |
185 | state is only seen in the event source preparation handler | |
186 | that is invoked from the | |
187 | <function>sd_event_prepare()</function> call and is | |
188 | immediately followed by <constant>SD_EVENT_ARMED</constant> or | |
189 | <constant>SD_EVENT_PENDING</constant>.</para></listitem> | |
190 | </varlistentry> | |
191 | ||
192 | <varlistentry> | |
193 | <term><constant>SD_EVENT_ARMED</constant></term> | |
194 | ||
195 | <listitem><para><function>sd_event_prepare()</function> has | |
196 | been called and no event sources were ready to be | |
197 | dispatched. Use <function>sd_event_wait()</function> to wait | |
198 | for new events, and transition into | |
199 | <constant>SD_EVENT_PENDING</constant> or back into | |
200 | <constant>SD_EVENT_INITIAL</constant>.</para></listitem> | |
201 | </varlistentry> | |
202 | ||
203 | <varlistentry> | |
204 | <term><constant>SD_EVENT_PENDING</constant></term> | |
205 | ||
206 | <listitem><para><function>sd_event_prepare()</function> or | |
207 | <function>sd_event_wait()</function> have been called and | |
208 | there were event sources with events pending. Use | |
209 | <function>sd_event_dispatch()</function> to dispatch the | |
210 | highest priority event source and transition back to | |
211 | <constant>SD_EVENT_INITIAL</constant>, or | |
212 | <constant>SD_EVENT_FINISHED</constant>.</para></listitem> | |
213 | </varlistentry> | |
214 | ||
215 | <varlistentry> | |
216 | <term><constant>SD_EVENT_RUNNING</constant></term> | |
217 | ||
218 | <listitem><para>A regular event source is currently being | |
219 | dispatched. This state is only seen in the event source | |
220 | handler that is invoked from the | |
221 | <function>sd_event_dispatch()</function> call, and is | |
222 | immediately followed by <constant>SD_EVENT_INITIAL</constant> | |
223 | or <constant>SD_EVENT_FINISHED</constant> as soon the event | |
224 | source handler returns. Note that during dispatching of exit | |
225 | event sources the <constant>SD_EVENT_EXITING</constant> state | |
226 | is seen instead.</para></listitem> | |
227 | </varlistentry> | |
228 | ||
229 | <varlistentry> | |
230 | <term><constant>SD_EVENT_EXITING</constant></term> | |
231 | ||
232 | <listitem><para>Similar to | |
233 | <constant>SD_EVENT_RUNNING</constant> but is the state in | |
234 | effect while dispatching exit event sources. It is followed by | |
235 | <constant>SD_EVENT_INITIAL</constant> or | |
236 | <constant>SD_EVENT_FINISHED</constant> as soon as the event | |
237 | handler returns.</para></listitem> | |
238 | </varlistentry> | |
239 | ||
240 | <varlistentry> | |
241 | <term><constant>SD_EVENT_FINISHED</constant></term> | |
242 | ||
243 | <listitem><para>The event loop has exited. All exit event | |
244 | sources have run. If the event loop is in this state it serves | |
245 | no purpose anymore, and should be freed.</para></listitem> | |
246 | </varlistentry> | |
247 | ||
248 | </variablelist> | |
249 | ||
250 | <para>A simplified flow chart of the states and the calls to | |
251 | transition between them is shown below. Note that | |
252 | <constant>SD_EVENT_PREPARING</constant>, | |
253 | <constant>SD_EVENT_RUNNING</constant> and | |
254 | <constant>SD_EVENT_EXITING</constant> are not shown here.</para> | |
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255 | |
256 | <programlisting> | |
dc83f27a LP |
257 | INITIAL -<---<---<---<---<---<---<---<---<---<---<---<---\ |
258 | | | | |
259 | | ^ | |
260 | | | | |
261 | v ret == 0 | | |
262 | sd_event_prepare() >--->--->--->--->- ARMED | | |
263 | | | ^ | |
264 | | ret > 0 | | | |
265 | | | | | |
266 | v v ret == 0 | | |
267 | PENDING <---<---<---<---<---< sd_event_wait() >--->--->--+ | |
268 | | ret > 0 ^ | |
269 | | | | |
270 | | | | |
271 | v | | |
272 | sd_event_dispatch() >--->--->--->--->--->--->--->--->--->--->/ | |
273 | | ret > 0 | |
274 | | ret == 0 | |
275 | | | |
276 | v | |
277 | FINISHED | |
42f1ab50 | 278 | </programlisting> |
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279 | </refsect1> |
280 | ||
281 | <refsect1> | |
282 | <title>Return Value</title> | |
283 | ||
284 | <para>On success, these functions return 0 or a positive integer. | |
285 | On failure, they return a negative errno-style error code. In case | |
dc83f27a LP |
286 | of <function>sd_event_prepare()</function> and |
287 | <function>sd_event_wait()</function>, a positive, non-zero return | |
288 | code indicates that events are ready to be processed and zero | |
289 | indicates that no events are ready. In case of | |
290 | <function>sd_event_dispatch()</function>, a positive, non-zero | |
291 | return code indicates that the event loop returned to its initial | |
292 | state and zero indicates the event loop has | |
293 | exited. <function>sd_event_get_state()</function> returns a | |
294 | positive or zero state on success.</para> | |
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295 | </refsect1> |
296 | ||
297 | <refsect1> | |
298 | <title>Errors</title> | |
299 | ||
300 | <para>Returned errors may indicate the following problems:</para> | |
301 | ||
302 | <variablelist> | |
303 | <varlistentry> | |
304 | <term><constant>-EINVAL</constant></term> | |
305 | ||
a8eaaee7 | 306 | <listitem><para>The <parameter>event</parameter> parameter is |
dc83f27a | 307 | invalid or <constant>NULL</constant>.</para></listitem> |
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308 | </varlistentry> |
309 | ||
310 | <varlistentry> | |
311 | <term><constant>-EBUSY</constant></term> | |
312 | ||
313 | <listitem><para>The event loop object is not in the right | |
314 | state.</para></listitem> | |
315 | </varlistentry> | |
316 | ||
317 | <varlistentry> | |
318 | <term><constant>-ESTALE</constant></term> | |
319 | ||
320 | <listitem><para>The event loop is already terminated.</para></listitem> | |
321 | ||
322 | </varlistentry> | |
323 | ||
324 | <varlistentry> | |
325 | <term><constant>-ECHILD</constant></term> | |
326 | ||
327 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
328 | ||
329 | </varlistentry> | |
330 | ||
331 | </variablelist> | |
332 | ||
b938cb90 | 333 | <para>Other errors are possible, too.</para> |
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334 | </refsect1> |
335 | ||
dc83f27a | 336 | <xi:include href="libsystemd-pkgconfig.xml" /> |
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337 | |
338 | <refsect1> | |
339 | <title>See Also</title> | |
340 | ||
341 | <para> | |
342 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
343 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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344 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
345 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
346 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
347 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
348 | <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
dc83f27a LP |
349 | <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
350 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
351 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
352 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
42f1ab50 ZJS |
353 | </para> |
354 | </refsect1> | |
355 | ||
356 | </refentry> |