man/sd_event_add_time.xml

   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+ -->
   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_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>
  25     <refname>sd_event_time_handler_t</refname>
  26
  27     <refpurpose>Add a timer event source to an event loop</refpurpose>
  28   </refnamediv>
  29
  30   <refsynopsisdiv>
  31     <funcsynopsis>
  32       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</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>
  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>
  51         <paramdef>void *<parameter>userdata</parameter></paramdef>
  52       </funcprototype>
  53
  54       <funcprototype>
  55         <funcdef>int <function>sd_event_add_time_relative</function></funcdef>
  56         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  57         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  58         <paramdef>clockid_t <parameter>clock</parameter></paramdef>
  59         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  60         <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
  61         <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
  62         <paramdef>void *<parameter>userdata</parameter></paramdef>
  63       </funcprototype>
  64
  65       <funcprototype>
  66         <funcdef>int <function>sd_event_source_get_time</function></funcdef>
  67         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  68         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  69       </funcprototype>
  70
  71       <funcprototype>
  72         <funcdef>int <function>sd_event_source_set_time</function></funcdef>
  73         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  74         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  75       </funcprototype>
  76
  77       <funcprototype>
  78         <funcdef>int <function>sd_event_source_set_time_relative</function></funcdef>
  79         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  80         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  81       </funcprototype>
  82
  83       <funcprototype>
  84         <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
  85         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  86         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  87       </funcprototype>
  88
  89       <funcprototype>
  90         <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
  91         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  92         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  93       </funcprototype>
  94
  95       <funcprototype>
  96         <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
  97         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  98         <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
  99       </funcprototype>
 100
 101     </funcsynopsis>
 102   </refsynopsisdiv>
 103
 104   <refsect1>
 105     <title>Description</title>
 106
 107     <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
 108     object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
 109     <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
 110     of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
 111     <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
 112     <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
 113     regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
 114     microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
 115     is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
 116     dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
 117     which may be used as an alternative to explicitly disabling a timer event source with
 118     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
 119     <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
 120     timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
 121     accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
 122     substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
 123     improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
 124     the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
 125     chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
 126     slightly later, subject to the specified accuracy value, the kernel timer slack (see
 127     <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
 128     scheduling latencies. To query the actual time the handler was called use
 129     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 130
 131     <para>By default, the timer will elapse once
 132     (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
 133     with
 134     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 135     If the handler function returns a negative error code, it will be
 136     disabled after the invocation, even if the
 137     <constant>SD_EVENT_ON</constant> mode was requested before. Note
 138     that a timer event set to <constant>SD_EVENT_ON</constant> will
 139     fire continuously unless its configured time is updated using
 140     <function>sd_event_source_set_time()</function>.
 141     </para>
 142
 143     <para><function>sd_event_add_time_relative()</function> is like <function>sd_event_add_time()</function>,
 144     but takes a relative time specification. It's relative to the current time of the event loop iteration,
 145     as returned by
 146     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 147
 148     <para>To destroy an event source object use
 149     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 150     but note that the event source is only removed from the event loop
 151     when all references to the event source are dropped. To make sure
 152     an event source does not fire anymore, even if it is still referenced,
 153     disable the event source using
 154     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 155     with <constant>SD_EVENT_OFF</constant>.</para>
 156
 157     <para>If the second parameter of
 158     <function>sd_event_add_time()</function> is
 159     <constant>NULL</constant> no reference to the event source object
 160     is returned. In this case the event source is considered
 161     "floating", and will be destroyed implicitly when the event loop
 162     itself is destroyed.</para>
 163
 164     <para>If the <parameter>handler</parameter> to
 165     <function>sd_event_add_time()</function> is
 166     <constant>NULL</constant>, and the event source fires, this will
 167     be considered a request to exit the event loop. In this case, the
 168     <parameter>userdata</parameter> parameter, cast to an integer, is
 169     used for the exit code passed to
 170     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 171
 172     <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
 173     <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
 174     that may wake up the system from suspend.</para>
 175
 176     <para>In order to set up relative timers (that is, relative to the
 177     current time), retrieve the current time via
 178     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 179     add the desired timespan to it, and use the result as
 180     the <parameter>usec</parameter> parameter to
 181     <function>sd_event_add_time()</function>.</para>
 182
 183     <para>In order to set up repetitive timers (that is, timers that
 184     are triggered in regular intervals), set up the timer normally,
 185     for the first invocation. Each time the event handler is invoked,
 186     update the timer's trigger time with
 187     <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
 188     iteration, and reenable the timer using
 189     <function>sd_event_source_set_enabled()</function>. To calculate
 190     the next point in time to pass to
 191     <function>sd_event_source_set_time()</function>, either use as
 192     base the <parameter>usec</parameter> parameter passed to the timer
 193     callback, or the timestamp returned by
 194     <function>sd_event_now()</function>. In the former case timer
 195     events will be regular, while in the latter case the scheduling
 196     latency will keep accumulating on the timer.</para>
 197
 198     <para><function>sd_event_source_get_time()</function> retrieves the configured time value of an event
 199     source created previously with <function>sd_event_add_time()</function> or
 200     <function>sd_event_add_time_relative()</function>. It takes the event source object and a pointer to a
 201     variable to store the time in, relative to the selected clock's epoch, in µs. The returned value is
 202     relative to the epoch, even if the event source was created with a relative time via
 203     <function>sd_event_add_time_relative()</function>.</para>
 204
 205     <para><function>sd_event_source_set_time()</function> changes the time of an event source created
 206     previously with <function>sd_event_add_time()</function> or
 207     <function>sd_event_add_time_relative()</function>. It takes the event source object and a time relative
 208     to the selected clock's epoch, in µs.</para>
 209
 210     <para><function>sd_event_source_set_time_relative()</function> is similar to
 211     <function>sd_event_source_set_time()</function>, but takes a time relative to the current time of the
 212     event loop iteration, as returned by <function>sd_event_now()</function>.</para>
 213
 214     <para><function>sd_event_source_get_time_accuracy()</function>
 215     retrieves the configured accuracy value of an event source
 216     created previously with <function>sd_event_add_time()</function>. It
 217     takes the event source object and a pointer to a variable to store
 218     the accuracy in. The accuracy is specified in µs.</para>
 219
 220     <para><function>sd_event_source_set_time_accuracy()</function>
 221     changes the configured accuracy of a timer event source created
 222     previously with <function>sd_event_add_time()</function>. It takes
 223     the event source object and accuracy, in µs.</para>
 224
 225     <para><function>sd_event_source_get_time_clock()</function>
 226     retrieves the configured clock of an event source created
 227     previously with <function>sd_event_add_time()</function>. It takes
 228     the event source object and a pointer to a variable to store the
 229     clock identifier in.</para>
 230   </refsect1>
 231
 232   <refsect1>
 233     <title>Return Value</title>
 234
 235     <para>On success, these functions return 0 or a positive
 236     integer. On failure, they return a negative errno-style error
 237     code. </para>
 238
 239     <refsect2>
 240       <title>Errors</title>
 241
 242       <para>Returned values may indicate the following problems:</para>
 243
 244       <variablelist>
 245         <varlistentry>
 246           <term><constant>-ENOMEM</constant></term>
 247
 248           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 249         </varlistentry>
 250
 251         <varlistentry>
 252           <term><constant>-EINVAL</constant></term>
 253
 254           <listitem><para>An invalid argument has been passed.</para></listitem>
 255
 256         </varlistentry>
 257
 258         <varlistentry>
 259           <term><constant>-ESTALE</constant></term>
 260
 261           <listitem><para>The event loop is already terminated.</para></listitem>
 262
 263         </varlistentry>
 264
 265         <varlistentry>
 266           <term><constant>-ECHILD</constant></term>
 267
 268           <listitem><para>The event loop has been created in a different process.</para></listitem>
 269
 270         </varlistentry>
 271
 272         <varlistentry>
 273           <term><constant>-EOPNOTSUPP</constant></term>
 274
 275           <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
 276
 277         </varlistentry>
 278
 279         <varlistentry>
 280           <term><constant>-EDOM</constant></term>
 281
 282           <listitem><para>The passed event source is not a timer event source.</para></listitem>
 283         </varlistentry>
 284
 285         <varlistentry>
 286           <term><constant>-EOVERFLOW</constant></term>
 287
 288           <listitem><para>The passed relative time is outside of the allowed range for time values (i.e. the
 289           specified value added to the current time is outside the 64 bit unsigned integer range).</para></listitem>
 290         </varlistentry>
 291       </variablelist>
 292     </refsect2>
 293   </refsect1>
 294
 295   <xi:include href="libsystemd-pkgconfig.xml" />
 296
 297   <refsect1>
 298     <title>See Also</title>
 299
 300     <para>
 301       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 302       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 303       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 304       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 305       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 306       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 307       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 308       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 309       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 310       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 311       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 312       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 313       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 314       <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 315       <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 316       <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 317       <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 318     </para>
 319   </refsect1>
 320
 321 </refentry>