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