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[thirdparty/systemd.git] / man / sd_event_now.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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  SPDX-License-Identifier: LGPL-2.1+
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<refentry id="sd_event_now" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_event_now</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_now</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_now</refname>

    <refpurpose>Retrieve current event loop iteration timestamp</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_event_now</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
        <paramdef>clockid_t <parameter>clock</parameter></paramdef>
        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_now()</function> returns the time when
    the most recent event loop iteration began. A timestamp
    is taken right after returning from the event sleep, and before
    dispatching any event sources. The <parameter>event</parameter>
    parameter specifies the event loop object to retrieve the timestamp
    from. The <parameter>clock</parameter> parameter specifies the clock to
    retrieve the timestamp for, and is one of
    <constant>CLOCK_REALTIME</constant> (or equivalently
    <constant>CLOCK_REALTIME_ALARM</constant>),
    <constant>CLOCK_MONOTONIC</constant>, or
    <constant>CLOCK_BOOTTIME</constant> (or equivalently
    <constant>CLOCK_BOOTTIME_ALARM</constant>), see
    <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    for more information on the various clocks. The retrieved
    timestamp is stored in the <parameter>usec</parameter> parameter,
    in µs since the clock's epoch. If this function is invoked before
    the first event loop iteration, the current time is returned, as
    reported by <function>clock_gettime()</function>. To distinguish
    this case from a regular invocation the return value will be
    positive, and zero when the returned timestamp refers to an actual
    event loop iteration.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>If the first event loop iteration has not run yet
    <function>sd_event_now()</function> writes current time to
    <parameter>usec</parameter> and returns a positive return value.
    Otherwise, it will write the requested timestamp to <parameter>usec</parameter>
    and return 0. On failure, the call returns a negative errno-style
    error code.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>Returned values may indicate the following problems:</para>

    <variablelist>
      <varlistentry>
        <term><constant>-EINVAL</constant></term>

        <listitem><para>An invalid parameter was
        passed.</para></listitem>

      </varlistentry>

      <varlistentry>
        <term><constant>-EOPNOTSUPP</constant></term>

        <listitem><para>Unsupported clock type.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ECHILD</constant></term>

        <listitem><para>The event loop object was created in a
        different process.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>