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> parameter to <function>sd_event_add_time()</function> is
 165     <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
 166     event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
 167     the exit code parameter to
 168     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 169
 170     <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
 171     <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
 172     that may wake up the system from suspend.</para>
 173
 174     <para>In order to set up relative timers (that is, relative to the
 175     current time), retrieve the current time via
 176     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 177     add the desired timespan to it, and use the result as
 178     the <parameter>usec</parameter> parameter to
 179     <function>sd_event_add_time()</function>.</para>
 180
 181     <para>In order to set up repetitive timers (that is, timers that
 182     are triggered in regular intervals), set up the timer normally,
 183     for the first invocation. Each time the event handler is invoked,
 184     update the timer's trigger time with
 185     <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
 186     iteration, and reenable the timer using
 187     <function>sd_event_source_set_enabled()</function>. To calculate
 188     the next point in time to pass to
 189     <function>sd_event_source_set_time()</function>, either use as
 190     base the <parameter>usec</parameter> parameter passed to the timer
 191     callback, or the timestamp returned by
 192     <function>sd_event_now()</function>. In the former case timer
 193     events will be regular, while in the latter case the scheduling
 194     latency will keep accumulating on the timer.</para>
 195
 196     <para><function>sd_event_source_get_time()</function> retrieves the configured time value of an event
 197     source created previously with <function>sd_event_add_time()</function> or
 198     <function>sd_event_add_time_relative()</function>. It takes the event source object and a pointer to a
 199     variable to store the time in, relative to the selected clock's epoch, in µs. The returned value is
 200     relative to the epoch, even if the event source was created with a relative time via
 201     <function>sd_event_add_time_relative()</function>.</para>
 202
 203     <para><function>sd_event_source_set_time()</function> changes the time of an event source created
 204     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 time relative
 206     to the selected clock's epoch, in µs.</para>
 207
 208     <para><function>sd_event_source_set_time_relative()</function> is similar to
 209     <function>sd_event_source_set_time()</function>, but takes a time relative to the current time of the
 210     event loop iteration, as returned by <function>sd_event_now()</function>.</para>
 211
 212     <para><function>sd_event_source_get_time_accuracy()</function>
 213     retrieves the configured accuracy value of an event source
 214     created previously with <function>sd_event_add_time()</function>. It
 215     takes the event source object and a pointer to a variable to store
 216     the accuracy in. The accuracy is specified in µs.</para>
 217
 218     <para><function>sd_event_source_set_time_accuracy()</function>
 219     changes the configured accuracy of a timer event source created
 220     previously with <function>sd_event_add_time()</function>. It takes
 221     the event source object and accuracy, in µs.</para>
 222
 223     <para><function>sd_event_source_get_time_clock()</function>
 224     retrieves the configured clock of an event source created
 225     previously with <function>sd_event_add_time()</function>. It takes
 226     the event source object and a pointer to a variable to store the
 227     clock identifier in.</para>
 228   </refsect1>
 229
 230   <refsect1>
 231     <title>Return Value</title>
 232
 233     <para>On success, these functions return 0 or a positive
 234     integer. On failure, they return a negative errno-style error
 235     code. </para>
 236
 237     <refsect2>
 238       <title>Errors</title>
 239
 240       <para>Returned values may indicate the following problems:</para>
 241
 242       <variablelist>
 243         <varlistentry>
 244           <term><constant>-ENOMEM</constant></term>
 245
 246           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 247         </varlistentry>
 248
 249         <varlistentry>
 250           <term><constant>-EINVAL</constant></term>
 251
 252           <listitem><para>An invalid argument has been passed.</para></listitem>
 253
 254         </varlistentry>
 255
 256         <varlistentry>
 257           <term><constant>-ESTALE</constant></term>
 258
 259           <listitem><para>The event loop is already terminated.</para></listitem>
 260
 261         </varlistentry>
 262
 263         <varlistentry>
 264           <term><constant>-ECHILD</constant></term>
 265
 266           <listitem><para>The event loop has been created in a different process.</para></listitem>
 267
 268         </varlistentry>
 269
 270         <varlistentry>
 271           <term><constant>-EOPNOTSUPP</constant></term>
 272
 273           <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
 274
 275         </varlistentry>
 276
 277         <varlistentry>
 278           <term><constant>-EDOM</constant></term>
 279
 280           <listitem><para>The passed event source is not a timer event source.</para></listitem>
 281         </varlistentry>
 282
 283         <varlistentry>
 284           <term><constant>-EOVERFLOW</constant></term>
 285
 286           <listitem><para>The passed relative time is outside of the allowed range for time values (i.e. the
 287           specified value added to the current time is outside the 64 bit unsigned integer range).</para></listitem>
 288         </varlistentry>
 289       </variablelist>
 290     </refsect2>
 291   </refsect1>
 292
 293   <xi:include href="libsystemd-pkgconfig.xml" />
 294
 295   <refsect1>
 296     <title>See Also</title>
 297
 298     <para>
 299       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 300       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 301       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 302       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 303       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 304       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 305       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 306       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 307       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 308       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 309       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 310       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 311       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 312       <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 313       <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 314       <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 315       <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 316     </para>
 317   </refsect1>
 318
 319 </refentry>