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514094f9 | 1 | <?xml version='1.0'?> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
42f1ab50 | 5 | |
dc83f27a | 6 | <refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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7 | |
8 | <refentryinfo> | |
9 | <title>sd_event_wait</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_event_wait</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_event_wait</refname> | |
20 | <refname>sd_event_prepare</refname> | |
21 | <refname>sd_event_dispatch</refname> | |
dc83f27a | 22 | <refname>sd_event_get_state</refname> |
60a3b1e1 | 23 | <refname>sd_event_get_iteration</refname> |
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24 | <refname>SD_EVENT_INITIAL</refname> |
25 | <refname>SD_EVENT_PREPARING</refname> | |
26 | <refname>SD_EVENT_ARMED</refname> | |
27 | <refname>SD_EVENT_PENDING</refname> | |
28 | <refname>SD_EVENT_RUNNING</refname> | |
29 | <refname>SD_EVENT_EXITING</refname> | |
30 | <refname>SD_EVENT_FINISHED</refname> | |
31 | ||
32 | <refpurpose>Low-level event loop operations</refpurpose> | |
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33 | </refnamediv> |
34 | ||
35 | <refsynopsisdiv> | |
36 | <funcsynopsis> | |
37 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
38 | ||
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39 | <funcsynopsisinfo><token>enum</token> { |
40 | <constant>SD_EVENT_INITIAL</constant>, | |
41 | <constant>SD_EVENT_PREPARING</constant>, | |
42 | <constant>SD_EVENT_ARMED</constant>, | |
43 | <constant>SD_EVENT_PENDING</constant>, | |
44 | <constant>SD_EVENT_RUNNING</constant>, | |
45 | <constant>SD_EVENT_EXITING</constant>, | |
46 | <constant>SD_EVENT_FINISHED</constant>, | |
47 | };</funcsynopsisinfo> | |
48 | ||
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49 | <funcprototype> |
50 | <funcdef>int <function>sd_event_prepare</function></funcdef> | |
51 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
52 | </funcprototype> | |
53 | ||
54 | <funcprototype> | |
55 | <funcdef>int <function>sd_event_wait</function></funcdef> | |
56 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
dc83f27a | 57 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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58 | </funcprototype> |
59 | ||
60 | <funcprototype> | |
61 | <funcdef>int <function>sd_event_dispatch</function></funcdef> | |
62 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
63 | </funcprototype> | |
64 | ||
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65 | <funcprototype> |
66 | <funcdef>int <function>sd_event_get_state</function></funcdef> | |
67 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
68 | </funcprototype> | |
69 | ||
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70 | <funcprototype> |
71 | <funcdef>int <function>sd_event_get_iteration</function></funcdef> | |
72 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
73 | <paramdef>uint64_t *<parameter>ret</parameter></paramdef> | |
74 | </funcprototype> | |
75 | ||
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76 | </funcsynopsis> |
77 | </refsynopsisdiv> | |
78 | ||
79 | <refsect1> | |
80 | <title>Description</title> | |
81 | ||
dc83f27a LP |
82 | <para>The low-level <function>sd_event_prepare()</function>, |
83 | <function>sd_event_wait()</function> and | |
84 | <function>sd_event_dispatch()</function> functions may be used to | |
85 | execute specific phases of an event loop. See | |
86 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
87 | and | |
88 | <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
89 | for higher-level functions that execute individual but complete | |
7f3fdb7f | 90 | iterations of an event loop or run it continuously.</para> |
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91 | |
92 | <para><function>sd_event_prepare()</function> checks for pending | |
42f1ab50 | 93 | events and arms necessary timers. If any events are ready to be |
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94 | processed ("pending"), it returns a positive, non-zero value, and the caller |
95 | should process these events with | |
96 | <function>sd_event_dispatch()</function>.</para> | |
97 | ||
98 | <para><function>sd_event_dispatch()</function> dispatches the | |
99 | highest priority event source that has a pending event. On | |
100 | success, <function>sd_event_dispatch()</function> returns either | |
101 | zero, which indicates that no further event sources may be | |
102 | dispatched and exiting of the event loop was requested via | |
103 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>; | |
104 | or a positive non-zero value, which means that an event source was | |
105 | dispatched and the loop returned to its initial state, and the | |
106 | caller should initiate the next event loop iteration by invoking | |
107 | <function>sd_event_prepare()</function> again.</para> | |
108 | ||
109 | <para>In case <function>sd_event_prepare()</function> returned | |
110 | zero, <function>sd_event_wait()</function> should be called to | |
111 | wait for further events or a timeout. If any events are ready to | |
112 | be processed, it returns a positive, non-zero value, and the | |
113 | events should be dispatched with | |
114 | <function>sd_event_dispatch()</function>. Otherwise, the event | |
115 | loop returned to its initial state and the next event loop | |
116 | iteration should be initiated by invoking | |
117 | <function>sd_event_prepare()</function> again.</para> | |
118 | ||
119 | <para><function>sd_event_get_state()</function> may be used to | |
120 | determine the state the event loop is currently in. It returns one | |
121 | of the states described below.</para> | |
122 | ||
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123 | <para><function>sd_event_get_iteration()</function> may be used to determine the current iteration of the event |
124 | loop. It returns an unsigned 64bit integer containing a counter that increases monotonically with each iteration of | |
125 | the event loop, starting with 0. The counter is increased at the time of the | |
126 | <function>sd_event_prepare()</function> invocation.</para> | |
127 | ||
128 | <para>All five functions take, as the first argument, the event loop object <parameter>event</parameter> that has | |
129 | been created with <function>sd_event_new()</function>. The timeout for <function>sd_event_wait()</function> is | |
130 | specified in <parameter>usec</parameter> in microseconds. <constant>(uint64_t) -1</constant> may be used to | |
131 | specify an infinite timeout.</para> | |
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132 | </refsect1> |
133 | ||
134 | <refsect1> | |
135 | <title>State Machine</title> | |
136 | ||
137 | <para>The event loop knows the following states, that may be | |
138 | queried with <function>sd_event_get_state()</function>.</para> | |
42f1ab50 | 139 | |
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140 | <variablelist> |
141 | <varlistentry> | |
142 | <term><constant>SD_EVENT_INITIAL</constant></term> | |
143 | ||
144 | <listitem><para>The initial state the event loop is in, | |
145 | before each event loop iteration. Use | |
146 | <function>sd_event_prepare()</function> to transition the | |
147 | event loop into the <constant>SD_EVENT_ARMED</constant> or | |
148 | <constant>SD_EVENT_PENDING</constant> states.</para></listitem> | |
149 | </varlistentry> | |
150 | ||
151 | <varlistentry> | |
152 | <term><constant>SD_EVENT_PREPARING</constant></term> | |
153 | ||
154 | <listitem><para>An event source is currently being prepared, | |
7f3fdb7f | 155 | i.e. the preparation handler is currently being executed, as |
dc83f27a | 156 | set with |
227bcd91 | 157 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This |
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158 | state is only seen in the event source preparation handler |
159 | that is invoked from the | |
160 | <function>sd_event_prepare()</function> call and is | |
161 | immediately followed by <constant>SD_EVENT_ARMED</constant> or | |
162 | <constant>SD_EVENT_PENDING</constant>.</para></listitem> | |
163 | </varlistentry> | |
164 | ||
165 | <varlistentry> | |
166 | <term><constant>SD_EVENT_ARMED</constant></term> | |
167 | ||
168 | <listitem><para><function>sd_event_prepare()</function> has | |
169 | been called and no event sources were ready to be | |
170 | dispatched. Use <function>sd_event_wait()</function> to wait | |
171 | for new events, and transition into | |
172 | <constant>SD_EVENT_PENDING</constant> or back into | |
173 | <constant>SD_EVENT_INITIAL</constant>.</para></listitem> | |
174 | </varlistentry> | |
175 | ||
176 | <varlistentry> | |
177 | <term><constant>SD_EVENT_PENDING</constant></term> | |
178 | ||
179 | <listitem><para><function>sd_event_prepare()</function> or | |
180 | <function>sd_event_wait()</function> have been called and | |
181 | there were event sources with events pending. Use | |
182 | <function>sd_event_dispatch()</function> to dispatch the | |
183 | highest priority event source and transition back to | |
184 | <constant>SD_EVENT_INITIAL</constant>, or | |
185 | <constant>SD_EVENT_FINISHED</constant>.</para></listitem> | |
186 | </varlistentry> | |
187 | ||
188 | <varlistentry> | |
189 | <term><constant>SD_EVENT_RUNNING</constant></term> | |
190 | ||
191 | <listitem><para>A regular event source is currently being | |
192 | dispatched. This state is only seen in the event source | |
193 | handler that is invoked from the | |
194 | <function>sd_event_dispatch()</function> call, and is | |
195 | immediately followed by <constant>SD_EVENT_INITIAL</constant> | |
196 | or <constant>SD_EVENT_FINISHED</constant> as soon the event | |
197 | source handler returns. Note that during dispatching of exit | |
198 | event sources the <constant>SD_EVENT_EXITING</constant> state | |
199 | is seen instead.</para></listitem> | |
200 | </varlistentry> | |
201 | ||
202 | <varlistentry> | |
203 | <term><constant>SD_EVENT_EXITING</constant></term> | |
204 | ||
205 | <listitem><para>Similar to | |
206 | <constant>SD_EVENT_RUNNING</constant> but is the state in | |
207 | effect while dispatching exit event sources. It is followed by | |
208 | <constant>SD_EVENT_INITIAL</constant> or | |
209 | <constant>SD_EVENT_FINISHED</constant> as soon as the event | |
210 | handler returns.</para></listitem> | |
211 | </varlistentry> | |
212 | ||
213 | <varlistentry> | |
214 | <term><constant>SD_EVENT_FINISHED</constant></term> | |
215 | ||
216 | <listitem><para>The event loop has exited. All exit event | |
217 | sources have run. If the event loop is in this state it serves | |
218 | no purpose anymore, and should be freed.</para></listitem> | |
219 | </varlistentry> | |
220 | ||
221 | </variablelist> | |
222 | ||
223 | <para>A simplified flow chart of the states and the calls to | |
224 | transition between them is shown below. Note that | |
225 | <constant>SD_EVENT_PREPARING</constant>, | |
226 | <constant>SD_EVENT_RUNNING</constant> and | |
227 | <constant>SD_EVENT_EXITING</constant> are not shown here.</para> | |
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228 | |
229 | <programlisting> | |
dc83f27a LP |
230 | INITIAL -<---<---<---<---<---<---<---<---<---<---<---<---\ |
231 | | | | |
232 | | ^ | |
233 | | | | |
234 | v ret == 0 | | |
235 | sd_event_prepare() >--->--->--->--->- ARMED | | |
236 | | | ^ | |
237 | | ret > 0 | | | |
238 | | | | | |
239 | v v ret == 0 | | |
240 | PENDING <---<---<---<---<---< sd_event_wait() >--->--->--+ | |
241 | | ret > 0 ^ | |
242 | | | | |
243 | | | | |
244 | v | | |
245 | sd_event_dispatch() >--->--->--->--->--->--->--->--->--->--->/ | |
246 | | ret > 0 | |
247 | | ret == 0 | |
248 | | | |
249 | v | |
250 | FINISHED | |
42f1ab50 | 251 | </programlisting> |
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252 | </refsect1> |
253 | ||
254 | <refsect1> | |
255 | <title>Return Value</title> | |
256 | ||
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257 | <para>On success, these functions return 0 or a positive integer. On failure, they return a negative |
258 | errno-style error code. In case of <function>sd_event_prepare()</function> and | |
259 | <function>sd_event_wait()</function>, a positive, non-zero return code indicates that events are ready to | |
260 | be processed and zero indicates that no events are ready. In case of | |
261 | <function>sd_event_dispatch()</function>, a positive, non-zero return code indicates that the event loop | |
262 | returned to its initial state and zero indicates the event loop has | |
263 | exited. <function>sd_event_get_state()</function> returns a positive or zero state on success.</para> | |
42f1ab50 | 264 | |
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265 | <refsect2> |
266 | <title>Errors</title> | |
42f1ab50 | 267 | |
b1de39de | 268 | <para>Returned errors may indicate the following problems:</para> |
42f1ab50 | 269 | |
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270 | <variablelist> |
271 | <varlistentry> | |
272 | <term><constant>-EINVAL</constant></term> | |
42f1ab50 | 273 | |
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274 | <listitem><para>The <parameter>event</parameter> parameter is invalid or <constant>NULL</constant>. |
275 | </para></listitem> | |
276 | </varlistentry> | |
42f1ab50 | 277 | |
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278 | <varlistentry> |
279 | <term><constant>-EBUSY</constant></term> | |
42f1ab50 | 280 | |
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281 | <listitem><para>The event loop object is not in the right state.</para></listitem> |
282 | </varlistentry> | |
42f1ab50 | 283 | |
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284 | <varlistentry> |
285 | <term><constant>-ESTALE</constant></term> | |
42f1ab50 | 286 | |
b1de39de | 287 | <listitem><para>The event loop is already terminated.</para></listitem> |
42f1ab50 | 288 | |
b1de39de | 289 | </varlistentry> |
42f1ab50 | 290 | |
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291 | <varlistentry> |
292 | <term><constant>-ECHILD</constant></term> | |
42f1ab50 | 293 | |
b1de39de | 294 | <listitem><para>The event loop has been created in a different process.</para></listitem> |
42f1ab50 | 295 | |
b1de39de | 296 | </varlistentry> |
42f1ab50 | 297 | |
b1de39de | 298 | </variablelist> |
42f1ab50 | 299 | |
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300 | <para>Other errors are possible, too.</para> |
301 | </refsect2> | |
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302 | </refsect1> |
303 | ||
dc83f27a | 304 | <xi:include href="libsystemd-pkgconfig.xml" /> |
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305 | |
306 | <refsect1> | |
307 | <title>See Also</title> | |
308 | ||
309 | <para> | |
310 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
311 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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312 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
313 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
314 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8274a30d LP |
315 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
316 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
42f1ab50 | 317 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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318 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
319 | <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
320 | <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
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321 | </para> |
322 | </refsect1> | |
323 | ||
324 | </refentry> |