man/sd_event_add_time.xml

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  10   Copyright 2014 Lennart Poettering
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  25
  26 <refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">
  27
  28   <refentryinfo>
  29     <title>sd_event_add_time</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_event_add_time</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_event_add_time</refname>
  49     <refname>sd_event_source_get_time</refname>
  50     <refname>sd_event_source_set_time</refname>
  51     <refname>sd_event_source_get_time_accuracy</refname>
  52     <refname>sd_event_source_set_time_accuracy</refname>
  53     <refname>sd_event_source_get_time_clock</refname>
  54     <refname>sd_event_time_handler_t</refname>
  55
  56     <refpurpose>Add a timer event source to an event loop</refpurpose>
  57   </refnamediv>
  58
  59   <refsynopsisdiv>
  60     <funcsynopsis>
  61       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  62
  63       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  64
  65       <funcprototype>
  66         <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
  67         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  68         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  69         <paramdef>void *<parameter>userdata</parameter></paramdef>
  70       </funcprototype>
  71
  72       <funcprototype>
  73         <funcdef>int <function>sd_event_add_time</function></funcdef>
  74         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  75         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  76         <paramdef>clockid_t <parameter>clock</parameter></paramdef>
  77         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
  78         <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
  79         <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
  80         <paramdef>void *<parameter>userdata</parameter></paramdef>
  81       </funcprototype>
  82
  83       <funcprototype>
  84         <funcdef>int <function>sd_event_source_get_time</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</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_accuracy</function></funcdef>
  97         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  98         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  99       </funcprototype>
 100
 101       <funcprototype>
 102         <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
 103         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
 104         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
 105       </funcprototype>
 106
 107       <funcprototype>
 108         <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
 109         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
 110         <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
 111       </funcprototype>
 112
 113     </funcsynopsis>
 114   </refsynopsisdiv>
 115
 116   <refsect1>
 117     <title>Description</title>
 118
 119     <para><function>sd_event_add_time()</function> adds a new timer event source to an event loop. The event loop
 120     object is specified in the <parameter>event</parameter> parameter, the event source object is returned in the
 121     <parameter>source</parameter> parameter. The <parameter>clock</parameter> parameter takes a clock identifier, one
 122     of <constant>CLOCK_REALTIME</constant>, <constant>CLOCK_MONOTONIC</constant>, <constant>CLOCK_BOOTTIME</constant>,
 123     <constant>CLOCK_REALTIME_ALARM</constant>, or <constant>CLOCK_BOOTTIME_ALARM</constant>. See
 124     <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details
 125     regarding the various types of clocks. The <parameter>usec</parameter> parameter specifies the earliest time, in
 126     microseconds (µs), relative to the clock's epoch, when the timer shall be triggered. If a time already in the past
 127     is specified (including <constant>0</constant>), this timer source "fires" immediately and is ready to be
 128     dispatched. If the parameter is specified as <constant>UINT64_MAX</constant> the timer event will never elapse,
 129     which may be used as an alternative to explicitly disabling a timer event source with
 130     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
 131     <parameter>accuracy</parameter> parameter specifies an additional accuracy value in µs specifying how much the
 132     timer event may be delayed. Use <constant>0</constant> to select the default accuracy (250ms). Use 1µs for maximum
 133     accuracy. Consider specifying 60000000µs (1min) or larger for long-running events that may be delayed
 134     substantially. Picking higher accuracy values allows the system to coalesce timer events more aggressively,
 135     improving power efficiency. The <parameter>handler</parameter> parameter shall reference a function to call when
 136     the timer elapses. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be
 137     chosen freely by the caller. The handler is also passed the configured trigger time, even if it is actually called
 138     slightly later, subject to the specified accuracy value, the kernel timer slack (see
 139     <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), and additional
 140     scheduling latencies. To query the actual time the handler was called use
 141     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 142
 143     <para>By default, the timer will elapse once
 144     (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
 145     with
 146     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 147     If the handler function returns a negative error code, it will be
 148     disabled after the invocation, even if the
 149     <constant>SD_EVENT_ON</constant> mode was requested before. Note
 150     that a timer event set to <constant>SD_EVENT_ON</constant> will
 151     fire continuously unless its configured time is updated using
 152     <function>sd_event_source_set_time()</function>.
 153     </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> to
 172     <function>sd_event_add_time()</function> is
 173     <constant>NULL</constant>, and the event source fires, this will
 174     be considered a request to exit the event loop. In this case, the
 175     <parameter>userdata</parameter> parameter, cast to an integer, is
 176     used for the exit code passed to
 177     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 178
 179     <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
 180     <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
 181     that may wake up the system from suspend.</para>
 182
 183     <para>In order to set up relative timers (that is, relative to the
 184     current time), retrieve the current time via
 185     <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 186     add the desired timespan to it, and use the result as
 187     the <parameter>usec</parameter> parameter to
 188     <function>sd_event_add_time()</function>.</para>
 189
 190     <para>In order to set up repetitive timers (that is, timers that
 191     are triggered in regular intervals), set up the timer normally,
 192     for the first invocation. Each time the event handler is invoked,
 193     update the timer's trigger time with
 194     <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
 195     iteration, and reenable the timer using
 196     <function>sd_event_source_set_enabled()</function>. To calculate
 197     the next point in time to pass to
 198     <function>sd_event_source_set_time()</function>, either use as
 199     base the <parameter>usec</parameter> parameter passed to the timer
 200     callback, or the timestamp returned by
 201     <function>sd_event_now()</function>. In the former case timer
 202     events will be regular, while in the latter case the scheduling
 203     latency will keep accumulating on the timer.</para>
 204
 205     <para><function>sd_event_source_get_time()</function> retrieves
 206     the configured time value of an event source created
 207     previously with <function>sd_event_add_time()</function>. It takes
 208     the event source object and a pointer to a variable to store the
 209     time in, relative to the selected clock's epoch, in µs.</para>
 210
 211     <para><function>sd_event_source_set_time()</function> changes the
 212     time of an event source created previously with
 213     <function>sd_event_add_time()</function>. It takes the event
 214     source object and a time relative to the selected clock's epoch,
 215     in µs.</para>
 216
 217     <para><function>sd_event_source_get_time_accuracy()</function>
 218     retrieves the configured accuracy value of an event source
 219     created previously with <function>sd_event_add_time()</function>. It
 220     takes the event source object and a pointer to a variable to store
 221     the accuracy in. The accuracy is specified in µs.</para>
 222
 223     <para><function>sd_event_source_set_time_accuracy()</function>
 224     changes the configured accuracy of a timer event source created
 225     previously with <function>sd_event_add_time()</function>. It takes
 226     the event source object and accuracy, in µs.</para>
 227
 228     <para><function>sd_event_source_get_time_clock()</function>
 229     retrieves the configured clock of an event source created
 230     previously with <function>sd_event_add_time()</function>. It takes
 231     the event source object and a pointer to a variable to store the
 232     clock identifier in.</para>
 233   </refsect1>
 234
 235   <refsect1>
 236     <title>Return Value</title>
 237
 238     <para>On success, these functions return 0 or a positive
 239     integer. On failure, they return a negative errno-style error
 240     code. </para>
 241   </refsect1>
 242
 243   <refsect1>
 244     <title>Errors</title>
 245
 246     <para>Returned values may indicate the following problems:</para>
 247
 248     <variablelist>
 249       <varlistentry>
 250         <term><constant>-ENOMEM</constant></term>
 251
 252         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 253       </varlistentry>
 254
 255       <varlistentry>
 256         <term><constant>-EINVAL</constant></term>
 257
 258         <listitem><para>An invalid argument has been passed.</para></listitem>
 259
 260       </varlistentry>
 261
 262       <varlistentry>
 263         <term><constant>-ESTALE</constant></term>
 264
 265         <listitem><para>The event loop is already terminated.</para></listitem>
 266
 267       </varlistentry>
 268
 269       <varlistentry>
 270         <term><constant>-ECHILD</constant></term>
 271
 272         <listitem><para>The event loop has been created in a different process.</para></listitem>
 273
 274       </varlistentry>
 275
 276       <varlistentry>
 277         <term><constant>-EOPNOTSUPP</constant></term>
 278
 279         <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>
 280
 281       </varlistentry>
 282
 283       <varlistentry>
 284         <term><constant>-EDOM</constant></term>
 285
 286         <listitem><para>The passed event source is not a timer event source.</para></listitem>
 287       </varlistentry>
 288     </variablelist>
 289   </refsect1>
 290
 291   <xi:include href="libsystemd-pkgconfig.xml" />
 292
 293   <refsect1>
 294     <title>See Also</title>
 295
 296     <para>
 297       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 298       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 299       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 300       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 301       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 302       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 303       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 304       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 305       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 306       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 307       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 308       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 309       <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 310       <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 311       <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 312     </para>
 313   </refsect1>
 314
 315 </refentry>