man/sd_event_now.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_now" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_event_now</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_event_now</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_event_now</refname>
  20
  21     <refpurpose>Retrieve current event loop iteration timestamp</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <funcsynopsis>
  26       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  27
  28       <funcprototype>
  29         <funcdef>int <function>sd_event_now</function></funcdef>
  30         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  31         <paramdef>clockid_t <parameter>clock</parameter></paramdef>
  32         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  33       </funcprototype>
  34
  35     </funcsynopsis>
  36   </refsynopsisdiv>
  37
  38   <refsect1>
  39     <title>Description</title>
  40
  41     <para><function>sd_event_now()</function> returns the time when
  42     the most recent event loop iteration began. A timestamp
  43     is taken right after returning from the event sleep, and before
  44     dispatching any event sources. The <parameter>event</parameter>
  45     parameter specifies the event loop object to retrieve the timestamp
  46     from. The <parameter>clock</parameter> parameter specifies the clock to
  47     retrieve the timestamp for, and is one of
  48     <constant>CLOCK_REALTIME</constant> (or equivalently
  49     <constant>CLOCK_REALTIME_ALARM</constant>),
  50     <constant>CLOCK_MONOTONIC</constant>, or
  51     <constant>CLOCK_BOOTTIME</constant> (or equivalently
  52     <constant>CLOCK_BOOTTIME_ALARM</constant>), see
  53     <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  54     for more information on the various clocks. The retrieved
  55     timestamp is stored in the <parameter>usec</parameter> parameter,
  56     in µs since the clock's epoch. If this function is invoked before
  57     the first event loop iteration, the current time is returned, as
  58     reported by <function>clock_gettime()</function>. To distinguish
  59     this case from a regular invocation the return value will be
  60     positive, and zero when the returned timestamp refers to an actual
  61     event loop iteration.</para>
  62   </refsect1>
  63
  64   <refsect1>
  65     <title>Return Value</title>
  66
  67     <para>If the first event loop iteration has not run yet
  68     <function>sd_event_now()</function> writes current time to
  69     <parameter>usec</parameter> and returns a positive return value.
  70     Otherwise, it will write the requested timestamp to <parameter>usec</parameter>
  71     and return 0. On failure, the call returns a negative errno-style
  72     error code.</para>
  73   </refsect1>
  74
  75   <refsect1>
  76     <title>Errors</title>
  77
  78     <para>Returned values may indicate the following problems:</para>
  79
  80     <variablelist>
  81       <varlistentry>
  82         <term><constant>-EINVAL</constant></term>
  83
  84         <listitem><para>An invalid parameter was
  85         passed.</para></listitem>
  86
  87       </varlistentry>
  88
  89       <varlistentry>
  90         <term><constant>-EOPNOTSUPP</constant></term>
  91
  92         <listitem><para>Unsupported clock type.
  93         </para></listitem>
  94       </varlistentry>
  95
  96       <varlistentry>
  97         <term><constant>-ECHILD</constant></term>
  98
  99         <listitem><para>The event loop object was created in a
 100         different process.</para></listitem>
 101       </varlistentry>
 102     </variablelist>
 103   </refsect1>
 104
 105   <xi:include href="libsystemd-pkgconfig.xml" />
 106
 107   <refsect1>
 108     <title>See Also</title>
 109
 110     <para>
 111       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 112       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 113       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 114       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 115       <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 116     </para>
 117   </refsect1>
 118
 119 </refentry>