man/sd_event_add_time.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   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, library or module instance.</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>