2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
6 <refentry id=
"sd_event_add_time" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
9 <title>sd_event_add_time
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>sd_event_add_time
</refentrytitle>
15 <manvolnum>3</manvolnum>
19 <refname>sd_event_add_time
</refname>
20 <refname>sd_event_add_time_relative
</refname>
21 <refname>sd_event_source_get_time
</refname>
22 <refname>sd_event_source_set_time
</refname>
23 <refname>sd_event_source_set_time_relative
</refname>
24 <refname>sd_event_source_get_time_accuracy
</refname>
25 <refname>sd_event_source_set_time_accuracy
</refname>
26 <refname>sd_event_source_get_time_clock
</refname>
27 <refname>sd_event_time_handler_t
</refname>
29 <refpurpose>Add a timer event source to an event loop
</refpurpose>
34 <funcsynopsisinfo>#include
<systemd/sd-event.h
></funcsynopsisinfo>
36 <funcsynopsisinfo><token>typedef
</token> struct sd_event_source sd_event_source;
</funcsynopsisinfo>
39 <funcdef>typedef int (*
<function>sd_event_time_handler_t
</function>)
</funcdef>
40 <paramdef>sd_event_source *
<parameter>s
</parameter></paramdef>
41 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
42 <paramdef>void *
<parameter>userdata
</parameter></paramdef>
46 <funcdef>int
<function>sd_event_add_time
</function></funcdef>
47 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
48 <paramdef>sd_event_source **
<parameter>source
</parameter></paramdef>
49 <paramdef>clockid_t
<parameter>clock
</parameter></paramdef>
50 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
51 <paramdef>uint64_t
<parameter>accuracy
</parameter></paramdef>
52 <paramdef>sd_event_time_handler_t
<parameter>handler
</parameter></paramdef>
53 <paramdef>void *
<parameter>userdata
</parameter></paramdef>
57 <funcdef>int
<function>sd_event_add_time_relative
</function></funcdef>
58 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
59 <paramdef>sd_event_source **
<parameter>source
</parameter></paramdef>
60 <paramdef>clockid_t
<parameter>clock
</parameter></paramdef>
61 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
62 <paramdef>uint64_t
<parameter>accuracy
</parameter></paramdef>
63 <paramdef>sd_event_time_handler_t
<parameter>handler
</parameter></paramdef>
64 <paramdef>void *
<parameter>userdata
</parameter></paramdef>
68 <funcdef>int
<function>sd_event_source_get_time
</function></funcdef>
69 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
70 <paramdef>uint64_t *
<parameter>usec
</parameter></paramdef>
74 <funcdef>int
<function>sd_event_source_set_time
</function></funcdef>
75 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
76 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
80 <funcdef>int
<function>sd_event_source_set_time_relative
</function></funcdef>
81 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
82 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
86 <funcdef>int
<function>sd_event_source_get_time_accuracy
</function></funcdef>
87 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
88 <paramdef>uint64_t *
<parameter>usec
</parameter></paramdef>
92 <funcdef>int
<function>sd_event_source_set_time_accuracy
</function></funcdef>
93 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
94 <paramdef>uint64_t
<parameter>usec
</parameter></paramdef>
98 <funcdef>int
<function>sd_event_source_get_time_clock
</function></funcdef>
99 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
100 <paramdef>clockid_t *
<parameter>clock
</parameter></paramdef>
107 <title>Description
</title>
109 <para><function>sd_event_add_time()
</function> adds a new timer event source to an event loop. The event loop
110 object is specified in the
<parameter>event
</parameter> parameter, the event source object is returned in the
111 <parameter>source
</parameter> parameter. The
<parameter>clock
</parameter> parameter takes a clock identifier, one
112 of
<constant>CLOCK_REALTIME
</constant>,
<constant>CLOCK_MONOTONIC
</constant>,
<constant>CLOCK_BOOTTIME
</constant>,
113 <constant>CLOCK_REALTIME_ALARM
</constant>, or
<constant>CLOCK_BOOTTIME_ALARM
</constant>. See
114 <citerefentry><refentrytitle>timerfd_create
</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
115 regarding the various types of clocks. The
<parameter>usec
</parameter> parameter specifies the earliest time, in
116 microseconds (μs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
117 is specified (including
<constant>0</constant>), this timer source
"fires" immediately and is ready to be
118 dispatched. If the parameter is specified as
<constant>UINT64_MAX
</constant> the timer event will never elapse,
119 which may be used as an alternative to explicitly disabling a timer event source with
120 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
121 <parameter>accuracy
</parameter> parameter specifies an additional accuracy value in μs specifying how much the
122 timer event may be delayed. Use
<constant>0</constant> to select the default accuracy (
250ms). Use
1μs for maximum
123 accuracy. Consider specifying
60000000μs (
1min) or larger for long-running events that may be delayed
124 substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
125 improving power efficiency.
</para>
127 <para>The
<parameter>handler
</parameter> is a function to call when the timer elapses or
128 <constant>NULL
</constant>. The
<parameter>userdata
</parameter> pointer will be passed to the handler
129 function, and may be chosen freely by the caller. The configured trigger time is also passed to the
130 handler, even if the call actually happens slightly later, subject to the specified accuracy value, the
131 kernel timer slack (see
132 <citerefentry><refentrytitle>prctl
</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and
133 additional scheduling latencies. To query the actual time the handler was called use
134 <citerefentry><refentrytitle>sd_event_now
</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
135 handler may return negative to signal an error (see below), other return values are ignored. If
136 <parameter>handler
</parameter> is
<constant>NULL
</constant>, a default handler that calls
137 <citerefentry><refentrytitle>sd_event_exit
</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
140 <para>By default, the timer will elapse once (
<constant>SD_EVENT_ONESHOT
</constant>), but this may be
142 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
143 If the handler function returns a negative error code, it will either be disabled after the invocation,
144 even if the
<constant>SD_EVENT_ON
</constant> mode was requested before, or it will cause the loop to
146 <citerefentry><refentrytitle>sd_event_source_set_exit_on_failure
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
147 Note that a timer event set to
<constant>SD_EVENT_ON
</constant> will fire continuously unless its
148 configured time is updated using
<function>sd_event_source_set_time()
</function>.
</para>
150 <para><function>sd_event_add_time_relative()
</function> is like
<function>sd_event_add_time()
</function>,
151 but takes a relative time specification. It's relative to the current time of the event loop iteration,
153 <citerefentry><refentrytitle>sd_event_now
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
155 <para>To destroy an event source object use
156 <citerefentry><refentrytitle>sd_event_source_unref
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
157 but note that the event source is only removed from the event loop
158 when all references to the event source are dropped. To make sure
159 an event source does not fire anymore, even if it is still referenced,
160 disable the event source using
161 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
162 with
<constant>SD_EVENT_OFF
</constant>.
</para>
164 <para>If the second parameter of
165 <function>sd_event_add_time()
</function> is
166 <constant>NULL
</constant> no reference to the event source object
167 is returned. In this case the event source is considered
168 "floating", and will be destroyed implicitly when the event loop
169 itself is destroyed.
</para>
171 <para>If the
<parameter>handler
</parameter> parameter to
<function>sd_event_add_time()
</function> is
172 <constant>NULL
</constant>, and the event source fires, this will be considered a request to exit the
173 event loop. In this case, the
<parameter>userdata
</parameter> parameter, cast to an integer, is passed as
174 the exit code parameter to
175 <citerefentry><refentrytitle>sd_event_exit
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
177 <para>Use
<constant>CLOCK_BOOTTIME_ALARM
</constant> and
178 <constant>CLOCK_REALTIME_ALARM
</constant> to define event sources
179 that may wake up the system from suspend.
</para>
181 <para>In order to set up relative timers (that is, relative to the
182 current time), retrieve the current time via
183 <citerefentry><refentrytitle>sd_event_now
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
184 add the desired timespan to it, and use the result as
185 the
<parameter>usec
</parameter> parameter to
186 <function>sd_event_add_time()
</function>.
</para>
188 <para>In order to set up repetitive timers (that is, timers that
189 are triggered in regular intervals), set up the timer normally,
190 for the first invocation. Each time the event handler is invoked,
191 update the timer's trigger time with
192 <citerefentry><refentrytitle>sd_event_source_set_time
</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
193 iteration, and reenable the timer using
194 <function>sd_event_source_set_enabled()
</function>. To calculate
195 the next point in time to pass to
196 <function>sd_event_source_set_time()
</function>, either use as
197 base the
<parameter>usec
</parameter> parameter passed to the timer
198 callback, or the timestamp returned by
199 <function>sd_event_now()
</function>. In the former case timer
200 events will be regular, while in the latter case the scheduling
201 latency will keep accumulating on the timer.
</para>
203 <para><function>sd_event_source_get_time()
</function> retrieves the configured time value of an event
204 source created previously with
<function>sd_event_add_time()
</function> or
205 <function>sd_event_add_time_relative()
</function>. It takes the event source object and a pointer to a
206 variable to store the time in, relative to the selected clock's epoch, in μs. The returned value is
207 relative to the epoch, even if the event source was created with a relative time via
208 <function>sd_event_add_time_relative()
</function>.
</para>
210 <para><function>sd_event_source_set_time()
</function> changes the time of an event source created
211 previously with
<function>sd_event_add_time()
</function> or
212 <function>sd_event_add_time_relative()
</function>. It takes the event source object and a time relative
213 to the selected clock's epoch, in μs.
</para>
215 <para><function>sd_event_source_set_time_relative()
</function> is similar to
216 <function>sd_event_source_set_time()
</function>, but takes a time relative to the current time of the
217 event loop iteration, as returned by
<function>sd_event_now()
</function>.
</para>
219 <para><function>sd_event_source_get_time_accuracy()
</function>
220 retrieves the configured accuracy value of an event source
221 created previously with
<function>sd_event_add_time()
</function>. It
222 takes the event source object and a pointer to a variable to store
223 the accuracy in. The accuracy is specified in μs.
</para>
225 <para><function>sd_event_source_set_time_accuracy()
</function>
226 changes the configured accuracy of a timer event source created
227 previously with
<function>sd_event_add_time()
</function>. It takes
228 the event source object and accuracy, in μs.
</para>
230 <para><function>sd_event_source_get_time_clock()
</function>
231 retrieves the configured clock of an event source created
232 previously with
<function>sd_event_add_time()
</function>. It takes
233 the event source object and a pointer to a variable to store the
234 clock identifier in.
</para>
238 <title>Return Value
</title>
240 <para>On success, these functions return
0 or a positive
241 integer. On failure, they return a negative errno-style error
245 <title>Errors
</title>
247 <para>Returned values may indicate the following problems:
</para>
251 <term><constant>-ENOMEM
</constant></term>
253 <listitem><para>Not enough memory to allocate an object.
</para></listitem>
257 <term><constant>-EINVAL
</constant></term>
259 <listitem><para>An invalid argument has been passed.
</para></listitem>
264 <term><constant>-ESTALE
</constant></term>
266 <listitem><para>The event loop is already terminated.
</para></listitem>
271 <term><constant>-ECHILD
</constant></term>
273 <listitem><para>The event loop has been created in a different process, library or module instance.
</para></listitem>
278 <term><constant>-EOPNOTSUPP
</constant></term>
280 <listitem><para>The selected clock is not supported by the event loop implementation.
</para></listitem>
285 <term><constant>-EDOM
</constant></term>
287 <listitem><para>The passed event source is not a timer event source.
</para></listitem>
291 <term><constant>-EOVERFLOW
</constant></term>
293 <listitem><para>The passed relative time is outside of the allowed range for time values (i.e. the
294 specified value added to the current time is outside the
64 bit unsigned integer range).
</para>
296 <xi:include href=
"version-info.xml" xpointer=
"v247"/></listitem>
302 <xi:include href=
"libsystemd-pkgconfig.xml" />
305 <title>History
</title>
306 <para><function>sd_event_add_time()
</function>,
307 <function>sd_event_source_get_time()
</function>,
308 <function>sd_event_source_set_time()
</function>,
309 <function>sd_event_source_get_time_accuracy()
</function>,
310 <function>sd_event_source_set_time_accuracy()
</function>, and
311 <function>sd_event_source_get_time_clock()
</function> were added in version
213.
</para>
312 <para><function>sd_event_time_handler_t()
</function> was added in version
217.
</para>
313 <para><function>sd_event_add_time_relative()
</function> and
314 <function>sd_event_source_set_time_relative()
</function> were added in version
247.
</para>
318 <title>See Also
</title>
320 <para><simplelist type=
"inline">
321 <member><citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
322 <member><citerefentry><refentrytitle>sd-event
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
323 <member><citerefentry><refentrytitle>sd_event_new
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
324 <member><citerefentry><refentrytitle>sd_event_now
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
325 <member><citerefentry><refentrytitle>sd_event_add_io
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
326 <member><citerefentry><refentrytitle>sd_event_add_signal
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
327 <member><citerefentry><refentrytitle>sd_event_add_child
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
328 <member><citerefentry><refentrytitle>sd_event_add_inotify
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
329 <member><citerefentry><refentrytitle>sd_event_add_defer
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
330 <member><citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
331 <member><citerefentry><refentrytitle>sd_event_source_set_priority
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
332 <member><citerefentry><refentrytitle>sd_event_source_set_userdata
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
333 <member><citerefentry><refentrytitle>sd_event_source_set_description
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
334 <member><citerefentry><refentrytitle>sd_event_source_set_floating
</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
335 <member><citerefentry project='man-pages'
><refentrytitle>clock_gettime
</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
336 <member><citerefentry project='man-pages'
><refentrytitle>timerfd_create
</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
337 <member><citerefentry project='man-pages'
><refentrytitle>prctl
</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>