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514094f9 | 1 | <?xml version='1.0'?> |
b408026b | 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 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
dc83f27a | 9 | <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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10 | |
11 | <refentryinfo> | |
12 | <title>sd_event_add_time</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_event_add_time</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_event_add_time</refname> | |
23 | <refname>sd_event_source_get_time</refname> | |
24 | <refname>sd_event_source_set_time</refname> | |
25 | <refname>sd_event_source_get_time_accuracy</refname> | |
26 | <refname>sd_event_source_set_time_accuracy</refname> | |
27 | <refname>sd_event_source_get_time_clock</refname> | |
dc83f27a | 28 | <refname>sd_event_time_handler_t</refname> |
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29 | |
30 | <refpurpose>Add a timer event source to an event loop</refpurpose> | |
31 | </refnamediv> | |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
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35 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
36 | ||
37 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
38 | ||
39 | <funcprototype> | |
40 | <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef> | |
41 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
42 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
43 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
44 | </funcprototype> | |
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45 | |
46 | <funcprototype> | |
47 | <funcdef>int <function>sd_event_add_time</function></funcdef> | |
48 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
49 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
50 | <paramdef>clockid_t <parameter>clock</parameter></paramdef> | |
51 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
52 | <paramdef>uint64_t <parameter>accuracy</parameter></paramdef> | |
53 | <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef> | |
3b3d7d06 | 54 | <paramdef>void *<parameter>userdata</parameter></paramdef> |
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55 | </funcprototype> |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>int <function>sd_event_source_get_time</function></funcdef> | |
59 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 60 | <paramdef>uint64_t *<parameter>usec</parameter></paramdef> |
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61 | </funcprototype> |
62 | ||
63 | <funcprototype> | |
64 | <funcdef>int <function>sd_event_source_set_time</function></funcdef> | |
65 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 66 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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67 | </funcprototype> |
68 | ||
69 | <funcprototype> | |
70 | <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef> | |
71 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 72 | <paramdef>uint64_t *<parameter>usec</parameter></paramdef> |
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73 | </funcprototype> |
74 | ||
75 | <funcprototype> | |
76 | <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef> | |
77 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 78 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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79 | </funcprototype> |
80 | ||
81 | <funcprototype> | |
82 | <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef> | |
83 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
84 | <paramdef>clockid_t *<parameter>clock</parameter></paramdef> | |
85 | </funcprototype> | |
86 | ||
87 | </funcsynopsis> | |
88 | </refsynopsisdiv> | |
89 | ||
90 | <refsect1> | |
91 | <title>Description</title> | |
92 | ||
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93 | <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop |
94 | object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the | |
95 | <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one | |
96 | of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>, | |
97 | <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See | |
98 | <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details | |
99 | regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in | |
100 | microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past | |
101 | is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be | |
595bfe7d | 102 | dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse, |
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103 | which may be used as an alternative to explicitly disabling a timer event source with |
104 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The | |
105 | <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the | |
106 | timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum | |
107 | accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed | |
108 | substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively, | |
109 | improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when | |
110 | the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be | |
111 | chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called | |
112 | slightly later, subject to the specified accuracy value, the kernel timer slack (see | |
113 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional | |
114 | scheduling latencies. To query the actual time the handler was called use | |
dc83f27a | 115 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> |
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116 | |
117 | <para>By default, the timer will elapse once | |
118 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
119 | with | |
120 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
121 | If the handler function returns a negative error code, it will be | |
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122 | disabled after the invocation, even if the |
123 | <constant>SD_EVENT_ON</constant> mode was requested before. Note | |
124 | that a timer event set to <constant>SD_EVENT_ON</constant> will | |
7f3fdb7f | 125 | fire continuously unless its configured time is updated using |
dc83f27a | 126 | <function>sd_event_source_set_time()</function>. |
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127 | </para> |
128 | ||
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129 | <para>To destroy an event source object use |
130 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
131 | but note that the event source is only removed from the event loop | |
132 | when all references to the event source are dropped. To make sure | |
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133 | an event source does not fire anymore, even if it is still referenced, |
134 | disable the event source using | |
135 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
136 | with <constant>SD_EVENT_OFF</constant>.</para> | |
dc83f27a | 137 | |
7f3fdb7f | 138 | <para>If the second parameter of |
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139 | <function>sd_event_add_time()</function> is |
140 | <constant>NULL</constant> no reference to the event source object | |
141 | is returned. In this case the event source is considered | |
142 | "floating", and will be destroyed implicitly when the event loop | |
143 | itself is destroyed.</para> | |
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144 | |
145 | <para>If the <parameter>handler</parameter> to | |
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146 | <function>sd_event_add_time()</function> is |
147 | <constant>NULL</constant>, and the event source fires, this will | |
148 | be considered a request to exit the event loop. In this case, the | |
149 | <parameter>userdata</parameter> parameter, cast to an integer, is | |
150 | used for the exit code passed to | |
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151 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> |
152 | ||
153 | <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and | |
154 | <constant>CLOCK_REALTIME_ALARM</constant> to define event sources | |
155 | that may wake up the system from suspend.</para> | |
156 | ||
157 | <para>In order to set up relative timers (that is, relative to the | |
158 | current time), retrieve the current time via | |
159 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
f23e83b1 | 160 | add the desired timespan to it, and use the result as |
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161 | the <parameter>usec</parameter> parameter to |
162 | <function>sd_event_add_time()</function>.</para> | |
163 | ||
164 | <para>In order to set up repetitive timers (that is, timers that | |
165 | are triggered in regular intervals), set up the timer normally, | |
166 | for the first invocation. Each time the event handler is invoked, | |
167 | update the timer's trigger time with | |
168 | <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer | |
169 | iteration, and reenable the timer using | |
170 | <function>sd_event_source_set_enabled()</function>. To calculate | |
171 | the next point in time to pass to | |
172 | <function>sd_event_source_set_time()</function>, either use as | |
173 | base the <parameter>usec</parameter> parameter passed to the timer | |
174 | callback, or the timestamp returned by | |
175 | <function>sd_event_now()</function>. In the former case timer | |
176 | events will be regular, while in the latter case the scheduling | |
177 | latency will keep accumulating on the timer.</para> | |
178 | ||
b408026b | 179 | <para><function>sd_event_source_get_time()</function> retrieves |
f23e83b1 | 180 | the configured time value of an event source created |
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181 | previously with <function>sd_event_add_time()</function>. It takes |
182 | the event source object and a pointer to a variable to store the | |
f23e83b1 | 183 | time in, relative to the selected clock's epoch, in µs.</para> |
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184 | |
185 | <para><function>sd_event_source_set_time()</function> changes the | |
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186 | time of an event source created previously with |
187 | <function>sd_event_add_time()</function>. It takes the event | |
188 | source object and a time relative to the selected clock's epoch, | |
189 | in µs.</para> | |
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190 | |
191 | <para><function>sd_event_source_get_time_accuracy()</function> | |
037a3ded | 192 | retrieves the configured accuracy value of an event source |
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193 | created previously with <function>sd_event_add_time()</function>. It |
194 | takes the event source object and a pointer to a variable to store | |
f23e83b1 | 195 | the accuracy in. The accuracy is specified in µs.</para> |
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196 | |
197 | <para><function>sd_event_source_set_time_accuracy()</function> | |
198 | changes the configured accuracy of a timer event source created | |
199 | previously with <function>sd_event_add_time()</function>. It takes | |
f23e83b1 | 200 | the event source object and accuracy, in µs.</para> |
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201 | |
202 | <para><function>sd_event_source_get_time_clock()</function> | |
037a3ded | 203 | retrieves the configured clock of an event source created |
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204 | previously with <function>sd_event_add_time()</function>. It takes |
205 | the event source object and a pointer to a variable to store the | |
206 | clock identifier in.</para> | |
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207 | </refsect1> |
208 | ||
209 | <refsect1> | |
210 | <title>Return Value</title> | |
211 | ||
212 | <para>On success, these functions return 0 or a positive | |
213 | integer. On failure, they return a negative errno-style error | |
214 | code. </para> | |
215 | </refsect1> | |
216 | ||
217 | <refsect1> | |
218 | <title>Errors</title> | |
219 | ||
f23e83b1 | 220 | <para>Returned values may indicate the following problems:</para> |
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221 | |
222 | <variablelist> | |
223 | <varlistentry> | |
8474b70c | 224 | <term><constant>-ENOMEM</constant></term> |
b408026b | 225 | |
3144ebca | 226 | <listitem><para>Not enough memory to allocate an object.</para></listitem> |
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227 | </varlistentry> |
228 | ||
229 | <varlistentry> | |
8474b70c | 230 | <term><constant>-EINVAL</constant></term> |
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231 | |
232 | <listitem><para>An invalid argument has been passed.</para></listitem> | |
233 | ||
234 | </varlistentry> | |
235 | ||
236 | <varlistentry> | |
8474b70c | 237 | <term><constant>-ESTALE</constant></term> |
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238 | |
239 | <listitem><para>The event loop is already terminated.</para></listitem> | |
240 | ||
241 | </varlistentry> | |
242 | ||
243 | <varlistentry> | |
8474b70c | 244 | <term><constant>-ECHILD</constant></term> |
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245 | |
246 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
247 | ||
248 | </varlistentry> | |
249 | ||
250 | <varlistentry> | |
15411c0c | 251 | <term><constant>-EOPNOTSUPP</constant></term> |
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252 | |
253 | <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem> | |
254 | ||
255 | </varlistentry> | |
b408026b | 256 | |
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257 | <varlistentry> |
258 | <term><constant>-EDOM</constant></term> | |
b408026b | 259 | |
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260 | <listitem><para>The passed event source is not a timer event source.</para></listitem> |
261 | </varlistentry> | |
262 | </variablelist> | |
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263 | </refsect1> |
264 | ||
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265 | <xi:include href="libsystemd-pkgconfig.xml" /> |
266 | ||
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267 | <refsect1> |
268 | <title>See Also</title> | |
269 | ||
270 | <para> | |
271 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
272 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
273 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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274 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
275 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
3144ebca | 276 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
edf25737 | 277 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
1eb54dc6 | 278 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
4dfefc19 | 279 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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280 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
281 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
282 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
283 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
284 | <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
285 | <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
286 | <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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287 | </para> |
288 | </refsect1> | |
289 | ||
290 | </refentry> |