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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+ --> |
b408026b | 5 | |
dc83f27a | 6 | <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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7 | |
8 | <refentryinfo> | |
9 | <title>sd_event_add_time</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_event_add_time</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_event_add_time</refname> | |
20 | <refname>sd_event_source_get_time</refname> | |
21 | <refname>sd_event_source_set_time</refname> | |
22 | <refname>sd_event_source_get_time_accuracy</refname> | |
23 | <refname>sd_event_source_set_time_accuracy</refname> | |
24 | <refname>sd_event_source_get_time_clock</refname> | |
dc83f27a | 25 | <refname>sd_event_time_handler_t</refname> |
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26 | |
27 | <refpurpose>Add a timer event source to an event loop</refpurpose> | |
28 | </refnamediv> | |
29 | ||
30 | <refsynopsisdiv> | |
31 | <funcsynopsis> | |
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32 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
33 | ||
34 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
35 | ||
36 | <funcprototype> | |
37 | <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef> | |
38 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
39 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
40 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
41 | </funcprototype> | |
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42 | |
43 | <funcprototype> | |
44 | <funcdef>int <function>sd_event_add_time</function></funcdef> | |
45 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
46 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
47 | <paramdef>clockid_t <parameter>clock</parameter></paramdef> | |
48 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> | |
49 | <paramdef>uint64_t <parameter>accuracy</parameter></paramdef> | |
50 | <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef> | |
3b3d7d06 | 51 | <paramdef>void *<parameter>userdata</parameter></paramdef> |
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52 | </funcprototype> |
53 | ||
54 | <funcprototype> | |
55 | <funcdef>int <function>sd_event_source_get_time</function></funcdef> | |
56 | <paramdef>sd_event_source *<parameter>source</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_source_set_time</function></funcdef> | |
62 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 63 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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64 | </funcprototype> |
65 | ||
66 | <funcprototype> | |
67 | <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef> | |
68 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 69 | <paramdef>uint64_t *<parameter>usec</parameter></paramdef> |
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70 | </funcprototype> |
71 | ||
72 | <funcprototype> | |
73 | <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef> | |
74 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
dc83f27a | 75 | <paramdef>uint64_t <parameter>usec</parameter></paramdef> |
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76 | </funcprototype> |
77 | ||
78 | <funcprototype> | |
79 | <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef> | |
80 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
81 | <paramdef>clockid_t *<parameter>clock</parameter></paramdef> | |
82 | </funcprototype> | |
83 | ||
84 | </funcsynopsis> | |
85 | </refsynopsisdiv> | |
86 | ||
87 | <refsect1> | |
88 | <title>Description</title> | |
89 | ||
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90 | <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop |
91 | object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the | |
92 | <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one | |
93 | of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>, | |
94 | <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See | |
95 | <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details | |
96 | regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in | |
97 | microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past | |
98 | is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be | |
595bfe7d | 99 | dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse, |
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100 | which may be used as an alternative to explicitly disabling a timer event source with |
101 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The | |
102 | <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the | |
103 | timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum | |
104 | accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed | |
105 | substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively, | |
106 | improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when | |
107 | the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be | |
108 | chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called | |
109 | slightly later, subject to the specified accuracy value, the kernel timer slack (see | |
110 | <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional | |
111 | scheduling latencies. To query the actual time the handler was called use | |
dc83f27a | 112 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> |
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113 | |
114 | <para>By default, the timer will elapse once | |
115 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
116 | with | |
117 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
118 | If the handler function returns a negative error code, it will be | |
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119 | disabled after the invocation, even if the |
120 | <constant>SD_EVENT_ON</constant> mode was requested before. Note | |
121 | that a timer event set to <constant>SD_EVENT_ON</constant> will | |
7f3fdb7f | 122 | fire continuously unless its configured time is updated using |
dc83f27a | 123 | <function>sd_event_source_set_time()</function>. |
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124 | </para> |
125 | ||
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126 | <para>To destroy an event source object use |
127 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
128 | but note that the event source is only removed from the event loop | |
129 | when all references to the event source are dropped. To make sure | |
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130 | an event source does not fire anymore, even if it is still referenced, |
131 | disable the event source using | |
132 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
133 | with <constant>SD_EVENT_OFF</constant>.</para> | |
dc83f27a | 134 | |
7f3fdb7f | 135 | <para>If the second parameter of |
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136 | <function>sd_event_add_time()</function> is |
137 | <constant>NULL</constant> no reference to the event source object | |
138 | is returned. In this case the event source is considered | |
139 | "floating", and will be destroyed implicitly when the event loop | |
140 | itself is destroyed.</para> | |
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141 | |
142 | <para>If the <parameter>handler</parameter> to | |
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143 | <function>sd_event_add_time()</function> is |
144 | <constant>NULL</constant>, and the event source fires, this will | |
145 | be considered a request to exit the event loop. In this case, the | |
146 | <parameter>userdata</parameter> parameter, cast to an integer, is | |
147 | used for the exit code passed to | |
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148 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> |
149 | ||
150 | <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and | |
151 | <constant>CLOCK_REALTIME_ALARM</constant> to define event sources | |
152 | that may wake up the system from suspend.</para> | |
153 | ||
154 | <para>In order to set up relative timers (that is, relative to the | |
155 | current time), retrieve the current time via | |
156 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
f23e83b1 | 157 | add the desired timespan to it, and use the result as |
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158 | the <parameter>usec</parameter> parameter to |
159 | <function>sd_event_add_time()</function>.</para> | |
160 | ||
161 | <para>In order to set up repetitive timers (that is, timers that | |
162 | are triggered in regular intervals), set up the timer normally, | |
163 | for the first invocation. Each time the event handler is invoked, | |
164 | update the timer's trigger time with | |
165 | <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer | |
166 | iteration, and reenable the timer using | |
167 | <function>sd_event_source_set_enabled()</function>. To calculate | |
168 | the next point in time to pass to | |
169 | <function>sd_event_source_set_time()</function>, either use as | |
170 | base the <parameter>usec</parameter> parameter passed to the timer | |
171 | callback, or the timestamp returned by | |
172 | <function>sd_event_now()</function>. In the former case timer | |
173 | events will be regular, while in the latter case the scheduling | |
174 | latency will keep accumulating on the timer.</para> | |
175 | ||
b408026b | 176 | <para><function>sd_event_source_get_time()</function> retrieves |
f23e83b1 | 177 | the configured time value of an event source created |
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178 | previously with <function>sd_event_add_time()</function>. It takes |
179 | the event source object and a pointer to a variable to store the | |
f23e83b1 | 180 | time in, relative to the selected clock's epoch, in µs.</para> |
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181 | |
182 | <para><function>sd_event_source_set_time()</function> changes the | |
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183 | time of an event source created previously with |
184 | <function>sd_event_add_time()</function>. It takes the event | |
185 | source object and a time relative to the selected clock's epoch, | |
186 | in µs.</para> | |
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187 | |
188 | <para><function>sd_event_source_get_time_accuracy()</function> | |
037a3ded | 189 | retrieves the configured accuracy value of an event source |
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190 | created previously with <function>sd_event_add_time()</function>. It |
191 | takes the event source object and a pointer to a variable to store | |
f23e83b1 | 192 | the accuracy in. The accuracy is specified in µs.</para> |
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193 | |
194 | <para><function>sd_event_source_set_time_accuracy()</function> | |
195 | changes the configured accuracy of a timer event source created | |
196 | previously with <function>sd_event_add_time()</function>. It takes | |
f23e83b1 | 197 | the event source object and accuracy, in µs.</para> |
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198 | |
199 | <para><function>sd_event_source_get_time_clock()</function> | |
037a3ded | 200 | retrieves the configured clock of an event source created |
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201 | previously with <function>sd_event_add_time()</function>. It takes |
202 | the event source object and a pointer to a variable to store the | |
203 | clock identifier in.</para> | |
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204 | </refsect1> |
205 | ||
206 | <refsect1> | |
207 | <title>Return Value</title> | |
208 | ||
209 | <para>On success, these functions return 0 or a positive | |
210 | integer. On failure, they return a negative errno-style error | |
211 | code. </para> | |
b408026b | 212 | |
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213 | <refsect2> |
214 | <title>Errors</title> | |
b408026b | 215 | |
b1de39de | 216 | <para>Returned values may indicate the following problems:</para> |
b408026b | 217 | |
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218 | <variablelist> |
219 | <varlistentry> | |
220 | <term><constant>-ENOMEM</constant></term> | |
b408026b | 221 | |
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222 | <listitem><para>Not enough memory to allocate an object.</para></listitem> |
223 | </varlistentry> | |
b408026b | 224 | |
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225 | <varlistentry> |
226 | <term><constant>-EINVAL</constant></term> | |
b408026b | 227 | |
b1de39de | 228 | <listitem><para>An invalid argument has been passed.</para></listitem> |
b408026b | 229 | |
b1de39de | 230 | </varlistentry> |
b408026b | 231 | |
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232 | <varlistentry> |
233 | <term><constant>-ESTALE</constant></term> | |
b408026b | 234 | |
b1de39de | 235 | <listitem><para>The event loop is already terminated.</para></listitem> |
b408026b | 236 | |
b1de39de | 237 | </varlistentry> |
b408026b | 238 | |
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239 | <varlistentry> |
240 | <term><constant>-ECHILD</constant></term> | |
b408026b | 241 | |
b1de39de | 242 | <listitem><para>The event loop has been created in a different process.</para></listitem> |
b408026b | 243 | |
b1de39de | 244 | </varlistentry> |
b408026b | 245 | |
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246 | <varlistentry> |
247 | <term><constant>-EOPNOTSUPP</constant></term> | |
b408026b | 248 | |
b1de39de | 249 | <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem> |
b408026b | 250 | |
b1de39de | 251 | </varlistentry> |
b408026b | 252 | |
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253 | <varlistentry> |
254 | <term><constant>-EDOM</constant></term> | |
b408026b | 255 | |
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256 | <listitem><para>The passed event source is not a timer event source.</para></listitem> |
257 | </varlistentry> | |
258 | </variablelist> | |
259 | </refsect2> | |
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260 | </refsect1> |
261 | ||
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262 | <xi:include href="libsystemd-pkgconfig.xml" /> |
263 | ||
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264 | <refsect1> |
265 | <title>See Also</title> | |
266 | ||
267 | <para> | |
268 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
269 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
270 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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271 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
272 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
3144ebca | 273 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
edf25737 | 274 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
1eb54dc6 | 275 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
4dfefc19 | 276 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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277 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
278 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
279 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
280 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
281 | <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
282 | <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, | |
283 | <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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284 | </para> |
285 | </refsect1> | |
286 | ||
287 | </refentry> |