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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 | <!-- | |
6 | SPDX-License-Identifier: LGPL-2.1+ | |
7 | ||
8 | This file is part of systemd. | |
9 | ||
10 | Copyright 2014 Lennart Poettering | |
11 | --> | |
12 | ||
13 | <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
14 | ||
15 | <refentryinfo> | |
16 | <title>sd_event_add_time</title> | |
17 | <productname>systemd</productname> | |
18 | ||
19 | <authorgroup> | |
20 | <author> | |
21 | <contrib>Developer</contrib> | |
22 | <firstname>Lennart</firstname> | |
23 | <surname>Poettering</surname> | |
24 | <email>lennart@poettering.net</email> | |
25 | </author> | |
26 | </authorgroup> | |
27 | </refentryinfo> | |
28 | ||
29 | <refmeta> | |
30 | <refentrytitle>sd_event_add_time</refentrytitle> | |
31 | <manvolnum>3</manvolnum> | |
32 | </refmeta> | |
33 | ||
34 | <refnamediv> | |
35 | <refname>sd_event_add_time</refname> | |
36 | <refname>sd_event_source_get_time</refname> | |
37 | <refname>sd_event_source_set_time</refname> | |
38 | <refname>sd_event_source_get_time_accuracy</refname> | |
39 | <refname>sd_event_source_set_time_accuracy</refname> | |
40 | <refname>sd_event_source_get_time_clock</refname> | |
41 | <refname>sd_event_time_handler_t</refname> | |
42 | ||
43 | <refpurpose>Add a timer event source to an event loop</refpurpose> | |
44 | </refnamediv> | |
45 | ||
46 | <refsynopsisdiv> | |
47 | <funcsynopsis> | |
48 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
49 | ||
50 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
51 | ||
52 | <funcprototype> | |
53 | <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef> | |
54 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
55 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
56 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
57 | </funcprototype> | |
58 | ||
59 | <funcprototype> | |
60 | <funcdef>int <function>sd_event_add_time</function></funcdef> | |
61 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
62 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
63 | <paramdef>clockid_t <parameter>clock</parameter></paramdef> | |
64 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
65 | <paramdef>uint64_t <parameter>accuracy</parameter></paramdef> | |
66 | <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef> | |
67 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
68 | </funcprototype> | |
69 | ||
70 | <funcprototype> | |
71 | <funcdef>int <function>sd_event_source_get_time</function></funcdef> | |
72 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
73 | <paramdef>uint64_t *<parameter>usec</parameter></paramdef> | |
74 | </funcprototype> | |
75 | ||
76 | <funcprototype> | |
77 | <funcdef>int <function>sd_event_source_set_time</function></funcdef> | |
78 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
79 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
80 | </funcprototype> | |
81 | ||
82 | <funcprototype> | |
83 | <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef> | |
84 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
85 | <paramdef>uint64_t *<parameter>usec</parameter></paramdef> | |
86 | </funcprototype> | |
87 | ||
88 | <funcprototype> | |
89 | <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef> | |
90 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
91 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
92 | </funcprototype> | |
93 | ||
94 | <funcprototype> | |
95 | <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef> | |
96 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
97 | <paramdef>clockid_t *<parameter>clock</parameter></paramdef> | |
98 | </funcprototype> | |
99 | ||
100 | </funcsynopsis> | |
101 | </refsynopsisdiv> | |
102 | ||
103 | <refsect1> | |
104 | <title>Description</title> | |
105 | ||
106 | <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop | |
107 | object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the | |
108 | <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one | |
109 | of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>, | |
110 | <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See | |
111 | <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details | |
112 | regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in | |
113 | microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past | |
114 | is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be | |
115 | dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse, | |
116 | which may be used as an alternative to explicitly disabling a timer event source with | |
117 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The | |
118 | <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the | |
119 | timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum | |
120 | accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed | |
121 | substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively, | |
122 | improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when | |
123 | the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be | |
124 | chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called | |
125 | slightly later, subject to the specified accuracy value, the kernel timer slack (see | |
126 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional | |
127 | scheduling latencies. To query the actual time the handler was called use | |
128 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
129 | ||
130 | <para>By default, the timer will elapse once | |
131 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
132 | with | |
133 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
134 | If the handler function returns a negative error code, it will be | |
135 | disabled after the invocation, even if the | |
136 | <constant>SD_EVENT_ON</constant> mode was requested before. Note | |
137 | that a timer event set to <constant>SD_EVENT_ON</constant> will | |
138 | fire continuously unless its configured time is updated using | |
139 | <function>sd_event_source_set_time()</function>. | |
140 | </para> | |
141 | ||
142 | <para>To destroy an event source object use | |
143 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
144 | but note that the event source is only removed from the event loop | |
145 | when all references to the event source are dropped. To make sure | |
146 | an event source does not fire anymore, even if it is still referenced, | |
147 | disable the event source using | |
148 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
149 | with <constant>SD_EVENT_OFF</constant>.</para> | |
150 | ||
151 | <para>If the second parameter of | |
152 | <function>sd_event_add_time()</function> is | |
153 | <constant>NULL</constant> no reference to the event source object | |
154 | is returned. In this case the event source is considered | |
155 | "floating", and will be destroyed implicitly when the event loop | |
156 | itself is destroyed.</para> | |
157 | ||
158 | <para>If the <parameter>handler</parameter> to | |
159 | <function>sd_event_add_time()</function> is | |
160 | <constant>NULL</constant>, and the event source fires, this will | |
161 | be considered a request to exit the event loop. In this case, the | |
162 | <parameter>userdata</parameter> parameter, cast to an integer, is | |
163 | used for the exit code passed to | |
164 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
165 | ||
166 | <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and | |
167 | <constant>CLOCK_REALTIME_ALARM</constant> to define event sources | |
168 | that may wake up the system from suspend.</para> | |
169 | ||
170 | <para>In order to set up relative timers (that is, relative to the | |
171 | current time), retrieve the current time via | |
172 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
173 | add the desired timespan to it, and use the result as | |
174 | the <parameter>usec</parameter> parameter to | |
175 | <function>sd_event_add_time()</function>.</para> | |
176 | ||
177 | <para>In order to set up repetitive timers (that is, timers that | |
178 | are triggered in regular intervals), set up the timer normally, | |
179 | for the first invocation. Each time the event handler is invoked, | |
180 | update the timer's trigger time with | |
181 | <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer | |
182 | iteration, and reenable the timer using | |
183 | <function>sd_event_source_set_enabled()</function>. To calculate | |
184 | the next point in time to pass to | |
185 | <function>sd_event_source_set_time()</function>, either use as | |
186 | base the <parameter>usec</parameter> parameter passed to the timer | |
187 | callback, or the timestamp returned by | |
188 | <function>sd_event_now()</function>. In the former case timer | |
189 | events will be regular, while in the latter case the scheduling | |
190 | latency will keep accumulating on the timer.</para> | |
191 | ||
192 | <para><function>sd_event_source_get_time()</function> retrieves | |
193 | the configured time value of an event source created | |
194 | previously with <function>sd_event_add_time()</function>. It takes | |
195 | the event source object and a pointer to a variable to store the | |
196 | time in, relative to the selected clock's epoch, in µs.</para> | |
197 | ||
198 | <para><function>sd_event_source_set_time()</function> changes the | |
199 | time of an event source created previously with | |
200 | <function>sd_event_add_time()</function>. It takes the event | |
201 | source object and a time relative to the selected clock's epoch, | |
202 | in µs.</para> | |
203 | ||
204 | <para><function>sd_event_source_get_time_accuracy()</function> | |
205 | retrieves the configured accuracy value of an event source | |
206 | created previously with <function>sd_event_add_time()</function>. It | |
207 | takes the event source object and a pointer to a variable to store | |
208 | the accuracy in. The accuracy is specified in µs.</para> | |
209 | ||
210 | <para><function>sd_event_source_set_time_accuracy()</function> | |
211 | changes the configured accuracy of a timer event source created | |
212 | previously with <function>sd_event_add_time()</function>. It takes | |
213 | the event source object and accuracy, in µs.</para> | |
214 | ||
215 | <para><function>sd_event_source_get_time_clock()</function> | |
216 | retrieves the configured clock of an event source created | |
217 | previously with <function>sd_event_add_time()</function>. It takes | |
218 | the event source object and a pointer to a variable to store the | |
219 | clock identifier in.</para> | |
220 | </refsect1> | |
221 | ||
222 | <refsect1> | |
223 | <title>Return Value</title> | |
224 | ||
225 | <para>On success, these functions return 0 or a positive | |
226 | integer. On failure, they return a negative errno-style error | |
227 | code. </para> | |
228 | </refsect1> | |
229 | ||
230 | <refsect1> | |
231 | <title>Errors</title> | |
232 | ||
233 | <para>Returned values may indicate the following problems:</para> | |
234 | ||
235 | <variablelist> | |
236 | <varlistentry> | |
237 | <term><constant>-ENOMEM</constant></term> | |
238 | ||
239 | <listitem><para>Not enough memory to allocate an object.</para></listitem> | |
240 | </varlistentry> | |
241 | ||
242 | <varlistentry> | |
243 | <term><constant>-EINVAL</constant></term> | |
244 | ||
245 | <listitem><para>An invalid argument has been passed.</para></listitem> | |
246 | ||
247 | </varlistentry> | |
248 | ||
249 | <varlistentry> | |
250 | <term><constant>-ESTALE</constant></term> | |
251 | ||
252 | <listitem><para>The event loop is already terminated.</para></listitem> | |
253 | ||
254 | </varlistentry> | |
255 | ||
256 | <varlistentry> | |
257 | <term><constant>-ECHILD</constant></term> | |
258 | ||
259 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
260 | ||
261 | </varlistentry> | |
262 | ||
263 | <varlistentry> | |
264 | <term><constant>-EOPNOTSUPP</constant></term> | |
265 | ||
266 | <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem> | |
267 | ||
268 | </varlistentry> | |
269 | ||
270 | <varlistentry> | |
271 | <term><constant>-EDOM</constant></term> | |
272 | ||
273 | <listitem><para>The passed event source is not a timer event source.</para></listitem> | |
274 | </varlistentry> | |
275 | </variablelist> | |
276 | </refsect1> | |
277 | ||
278 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
279 | ||
280 | <refsect1> | |
281 | <title>See Also</title> | |
282 | ||
283 | <para> | |
284 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
285 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
286 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
287 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
288 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
289 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
290 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
291 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
292 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
293 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
294 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
295 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
296 | <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
297 | <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
298 | <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
299 | </para> | |
300 | </refsect1> | |
301 | ||
302 | </refentry> |