1<?xml version='1.0'?>
2<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
5
6<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
7
8  <refentryinfo>
9    <title>sd_event_add_time</title>
10    <productname>systemd</productname>
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_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>
28
29    <refpurpose>Add a timer event source to an event loop</refpurpose>
30  </refnamediv>
31
32  <refsynopsisdiv>
33    <funcsynopsis>
34      <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
35
36      <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
37
38      <funcprototype>
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>
43      </funcprototype>
44
45      <funcprototype>
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>
54      </funcprototype>
55
56      <funcprototype>
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>
65      </funcprototype>
66
67      <funcprototype>
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>
71      </funcprototype>
72
73      <funcprototype>
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>
77      </funcprototype>
78
79      <funcprototype>
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>
83      </funcprototype>
84
85      <funcprototype>
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>
89      </funcprototype>
90
91      <funcprototype>
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>
95      </funcprototype>
96
97      <funcprototype>
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>
101      </funcprototype>
102
103    </funcsynopsis>
104  </refsynopsisdiv>
105
106  <refsect1>
107    <title>Description</title>
108
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>
126
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
138    used.</para>
139
140    <para>By default, the timer will elapse once (<constant>SD_EVENT_ONESHOT</constant>), but this may be
141    changed with
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
145    terminate, see
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>
149
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,
152    as returned by
153    <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
154
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>
163
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>
170
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>
176
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>
180
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>
187
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>
202
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>
209
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>
214
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>
218
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>
224
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>
229
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>
235  </refsect1>
236
237  <refsect1>
238    <title>Return Value</title>
239
240    <para>On success, these functions return 0 or a positive
241    integer. On failure, they return a negative errno-style error
242    code. </para>
243
244    <refsect2>
245      <title>Errors</title>
246
247      <para>Returned values may indicate the following problems:</para>
248
249      <variablelist>
250        <varlistentry>
251          <term><constant>-ENOMEM</constant></term>
252
253          <listitem><para>Not enough memory to allocate an object.</para></listitem>
254        </varlistentry>
255
256        <varlistentry>
257          <term><constant>-EINVAL</constant></term>
258
259          <listitem><para>An invalid argument has been passed.</para></listitem>
260
261        </varlistentry>
262
263        <varlistentry>
264          <term><constant>-ESTALE</constant></term>
265
266          <listitem><para>The event loop is already terminated.</para></listitem>
267
268        </varlistentry>
269
270        <varlistentry>
271          <term><constant>-ECHILD</constant></term>
272
273          <listitem><para>The event loop has been created in a different process.</para></listitem>
274
275        </varlistentry>
276
277        <varlistentry>
278          <term><constant>-EOPNOTSUPP</constant></term>
279
280          <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
281
282        </varlistentry>
283
284        <varlistentry>
285          <term><constant>-EDOM</constant></term>
286
287          <listitem><para>The passed event source is not a timer event source.</para></listitem>
288        </varlistentry>
289
290        <varlistentry>
291          <term><constant>-EOVERFLOW</constant></term>
292
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></listitem>
295        </varlistentry>
296      </variablelist>
297    </refsect2>
298  </refsect1>
299
300  <xi:include href="libsystemd-pkgconfig.xml" />
301
302  <refsect1>
303    <title>See Also</title>
304
305    <para>
306      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
307      <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
308      <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
309      <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
310      <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
311      <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
312      <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
313      <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
314      <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
315      <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
316      <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
317      <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
318      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
319      <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
320      <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
321      <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
322      <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
323    </para>
324  </refsect1>
325
326</refentry>
327