man/sd_event_add_time.xml

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   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
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  10   Copyright 2014 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>sd_event_add_time</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_event_add_time</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_event_add_time</refname>
  36     <refname>sd_event_source_get_time</refname>
  37     <refname>sd_event_source_set_time</refname>
  38     <refname>sd_event_source_get_time_accuracy</refname>
  39     <refname>sd_event_source_set_time_accuracy</refname>
  40     <refname>sd_event_source_get_time_clock</refname>
  41     <refname>sd_event_time_handler_t</refname>
  42
  43     <refpurpose>Add a timer event source to an event loop</refpurpose>
  44   </refnamediv>
  45
  46   <refsynopsisdiv>
  47     <funcsynopsis>
  48       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  49
  50       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  51
  52       <funcprototype>
  53         <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
  54         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  55         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  56         <paramdef>void *<parameter>userdata</parameter></paramdef>
  57       </funcprototype>
  58
  59       <funcprototype>
  60         <funcdef>int <function>sd_event_add_time</function></funcdef>
  61         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  62         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  63         <paramdef>clockid_t <parameter>clock</parameter></paramdef>
  64         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  65         <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
  66         <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
  67         <paramdef>void *<parameter>userdata</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>int <function>sd_event_source_get_time</function></funcdef>
  72         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  73         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  74       </funcprototype>
  75
  76       <funcprototype>
  77         <funcdef>int <function>sd_event_source_set_time</function></funcdef>
  78         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  79         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  80       </funcprototype>
  81
  82       <funcprototype>
  83         <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
  84         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  85         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  86       </funcprototype>
  87
  88       <funcprototype>
  89         <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
  90         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  91         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  92       </funcprototype>
  93
  94       <funcprototype>
  95         <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
  96         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  97         <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
  98       </funcprototype>
  99
 100     </funcsynopsis>
 101   </refsynopsisdiv>
 102
 103   <refsect1>
 104     <title>Description</title>
 105
 106     <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
 107     object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
 108     <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
 109     of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
 110     <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
 111     <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
 112     regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
 113     microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
 114     is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
 115     dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
 116     which may be used as an alternative to explicitly disabling a timer event source with
 117     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
 118     <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
 119     timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
 120     accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
 121     substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
 122     improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
 123     the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
 124     chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
 125     slightly later, subject to the specified accuracy value, the kernel timer slack (see
 126     <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
 127     scheduling latencies. To query the actual time the handler was called use
 128     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 129
 130     <para>By default, the timer will elapse once
 131     (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
 132     with
 133     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 134     If the handler function returns a negative error code, it will be
 135     disabled after the invocation, even if the
 136     <constant>SD_EVENT_ON</constant> mode was requested before. Note
 137     that a timer event set to <constant>SD_EVENT_ON</constant> will
 138     fire continuously unless its configured time is updated using
 139     <function>sd_event_source_set_time()</function>.
 140     </para>
 141
 142     <para>To destroy an event source object use
 143     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 144     but note that the event source is only removed from the event loop
 145     when all references to the event source are dropped. To make sure
 146     an event source does not fire anymore, even if it is still referenced,
 147     disable the event source using
 148     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 149     with <constant>SD_EVENT_OFF</constant>.</para>
 150
 151     <para>If the second parameter of
 152     <function>sd_event_add_time()</function> is
 153     <constant>NULL</constant> no reference to the event source object
 154     is returned. In this case the event source is considered
 155     "floating", and will be destroyed implicitly when the event loop
 156     itself is destroyed.</para>
 157
 158     <para>If the <parameter>handler</parameter> to
 159     <function>sd_event_add_time()</function> is
 160     <constant>NULL</constant>, and the event source fires, this will
 161     be considered a request to exit the event loop. In this case, the
 162     <parameter>userdata</parameter> parameter, cast to an integer, is
 163     used for the exit code passed to
 164     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 165
 166     <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
 167     <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
 168     that may wake up the system from suspend.</para>
 169
 170     <para>In order to set up relative timers (that is, relative to the
 171     current time), retrieve the current time via
 172     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 173     add the desired timespan to it, and use the result as
 174     the <parameter>usec</parameter> parameter to
 175     <function>sd_event_add_time()</function>.</para>
 176
 177     <para>In order to set up repetitive timers (that is, timers that
 178     are triggered in regular intervals), set up the timer normally,
 179     for the first invocation. Each time the event handler is invoked,
 180     update the timer's trigger time with
 181     <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
 182     iteration, and reenable the timer using
 183     <function>sd_event_source_set_enabled()</function>. To calculate
 184     the next point in time to pass to
 185     <function>sd_event_source_set_time()</function>, either use as
 186     base the <parameter>usec</parameter> parameter passed to the timer
 187     callback, or the timestamp returned by
 188     <function>sd_event_now()</function>. In the former case timer
 189     events will be regular, while in the latter case the scheduling
 190     latency will keep accumulating on the timer.</para>
 191
 192     <para><function>sd_event_source_get_time()</function> retrieves
 193     the configured time value of an event source created
 194     previously with <function>sd_event_add_time()</function>. It takes
 195     the event source object and a pointer to a variable to store the
 196     time in, relative to the selected clock's epoch, in µs.</para>
 197
 198     <para><function>sd_event_source_set_time()</function> changes the
 199     time of an event source created previously with
 200     <function>sd_event_add_time()</function>. It takes the event
 201     source object and a time relative to the selected clock's epoch,
 202     in µs.</para>
 203
 204     <para><function>sd_event_source_get_time_accuracy()</function>
 205     retrieves the configured accuracy value of an event source
 206     created previously with <function>sd_event_add_time()</function>. It
 207     takes the event source object and a pointer to a variable to store
 208     the accuracy in. The accuracy is specified in µs.</para>
 209
 210     <para><function>sd_event_source_set_time_accuracy()</function>
 211     changes the configured accuracy of a timer event source created
 212     previously with <function>sd_event_add_time()</function>. It takes
 213     the event source object and accuracy, in µs.</para>
 214
 215     <para><function>sd_event_source_get_time_clock()</function>
 216     retrieves the configured clock of an event source created
 217     previously with <function>sd_event_add_time()</function>. It takes
 218     the event source object and a pointer to a variable to store the
 219     clock identifier in.</para>
 220   </refsect1>
 221
 222   <refsect1>
 223     <title>Return Value</title>
 224
 225     <para>On success, these functions return 0 or a positive
 226     integer. On failure, they return a negative errno-style error
 227     code. </para>
 228   </refsect1>
 229
 230   <refsect1>
 231     <title>Errors</title>
 232
 233     <para>Returned values may indicate the following problems:</para>
 234
 235     <variablelist>
 236       <varlistentry>
 237         <term><constant>-ENOMEM</constant></term>
 238
 239         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 240       </varlistentry>
 241
 242       <varlistentry>
 243         <term><constant>-EINVAL</constant></term>
 244
 245         <listitem><para>An invalid argument has been passed.</para></listitem>
 246
 247       </varlistentry>
 248
 249       <varlistentry>
 250         <term><constant>-ESTALE</constant></term>
 251
 252         <listitem><para>The event loop is already terminated.</para></listitem>
 253
 254       </varlistentry>
 255
 256       <varlistentry>
 257         <term><constant>-ECHILD</constant></term>
 258
 259         <listitem><para>The event loop has been created in a different process.</para></listitem>
 260
 261       </varlistentry>
 262
 263       <varlistentry>
 264         <term><constant>-EOPNOTSUPP</constant></term>
 265
 266         <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
 267
 268       </varlistentry>
 269
 270       <varlistentry>
 271         <term><constant>-EDOM</constant></term>
 272
 273         <listitem><para>The passed event source is not a timer event source.</para></listitem>
 274       </varlistentry>
 275     </variablelist>
 276   </refsect1>
 277
 278   <xi:include href="libsystemd-pkgconfig.xml" />
 279
 280   <refsect1>
 281     <title>See Also</title>
 282
 283     <para>
 284       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 285       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 286       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 287       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 288       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 289       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 290       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 291       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 292       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 293       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 294       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 295       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 296       <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 297       <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 298       <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 299     </para>
 300   </refsect1>
 301
 302 </refentry>