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+
8 This file is part of systemd.
10 Copyright 2014 Lennart Poettering
13 <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
16 <title>sd_event_add_time</title>
17 <productname>systemd</productname>
21 <contrib>Developer</contrib>
22 <firstname>Lennart</firstname>
23 <surname>Poettering</surname>
24 <email>lennart@poettering.net</email>
30 <refentrytitle>sd_event_add_time</refentrytitle>
31 <manvolnum>3</manvolnum>
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>
43 <refpurpose>Add a timer event source to an event loop</refpurpose>
48 <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
50 <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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>
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>
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>
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>
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>
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>
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>
104 <title>Description</title>
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>
130 <para>By default, the timer will elapse once
131 (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
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>.
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>
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>
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>
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>
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>
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>
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>
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,
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>
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>
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>
223 <title>Return Value</title>
225 <para>On success, these functions return 0 or a positive
226 integer. On failure, they return a negative errno-style error
231 <title>Errors</title>
233 <para>Returned values may indicate the following problems:</para>
237 <term><constant>-ENOMEM</constant></term>
239 <listitem><para>Not enough memory to allocate an object.</para></listitem>
243 <term><constant>-EINVAL</constant></term>
245 <listitem><para>An invalid argument has been passed.</para></listitem>
250 <term><constant>-ESTALE</constant></term>
252 <listitem><para>The event loop is already terminated.</para></listitem>
257 <term><constant>-ECHILD</constant></term>
259 <listitem><para>The event loop has been created in a different process.</para></listitem>
264 <term><constant>-EOPNOTSUPP</constant></term>
266 <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
271 <term><constant>-EDOM</constant></term>
273 <listitem><para>The passed event source is not a timer event source.</para></listitem>
278 <xi:include href="libelogind-pkgconfig.xml" />
281 <title>See Also</title>
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_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
292 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
293 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
294 <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
295 <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
296 <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
297 <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
298 <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
299 <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>