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<refentry id="sd_event_add_time">

  <refentryinfo>
    <title>sd_event_add_time</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_add_time</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_add_time</refname>
    <refname>sd_event_source_get_time</refname>
    <refname>sd_event_source_set_time</refname>
    <refname>sd_event_source_get_time_accuracy</refname>
    <refname>sd_event_source_set_time_accuracy</refname>
    <refname>sd_event_source_get_time_clock</refname>

    <refpurpose>Add a timer event source to an event loop</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_event_add_time</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
        <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
        <paramdef>clockid_t <parameter>clock</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
        <paramdef>uint64_t <parameter>accuracy</parameter></paramdef>
        <paramdef>sd_event_time_handler_t <parameter>handler</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>typedef int (*<function>sd_event_time_handler_t</function>)</funcdef>
        <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
        <paramdef>uint64_t <parameter>usec</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_time</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>usec_t *<parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_set_time</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>usec_t <parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_time_accuracy</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>usec_t *<parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_set_time_accuracy</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>usec_t <parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_time_clock</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>clockid_t *<parameter>clock</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_add_time()</function> adds a new timer
    event source to an event loop object. The event loop is specified
    in <parameter>event</parameter>, the event source is returned in
    the <parameter>source</parameter> parameter. The
    <parameter>clock</parameter> parameter takes a clock identifier,
    one of <constant>CLOCK_REALTIME</constant>,
    <constant>CLOCK_MONOTONIC</constant> and
    <constant>CLOCK_BOOTTIME_ALARM</constant>. See
    <citerefentry><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    for details regarding the various types of clocks. The
    <parameter>usec</parameter> parameter takes a time value in
    microseconds, relative to the clock's epoch specifying when the
    timer shall elapse the earliest. The
    <parameter>accuracy</parameter> parameter takes an additional
    accuracy value in microseconds specifying a time the timer event
    may be delayed. Specify 0 for selecting the default accuracy
    (250ms). Specify 1 for most accurate timers. Consider specifying
    60000000 or larger (1h) for long-running events that may be
    delayed substantially. Picking higher accuracy values allows the
    system to coalesce timer events more aggressively, thus improving
    power efficiency. The <parameter>handler</parameter> shall
    reference a function to call when the timer elapses. The handler
    function will be passed the <parameter>userdata</parameter>
    pointer, which may be chosen freely by the caller. The handler is
    also passed the configured time it was triggered, however it might
    actually have been called at a slightly later time, subject to the
    specified accuracy value, the kernel timer slack (see
    <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>)
    and additional scheduling latencies.</para>

    <para>By default, the timer will elapse once
    (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
    with
    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    If the handler function returns a negative error code, it will be
    disabled after the invocation, even if
    <constant>SD_EVENT_ON</constant> mode is set.
    </para>

    <para><function>sd_event_source_get_time()</function> retrieves
    the configured time value of a timer event source created
    previously with <function>sd_event_add_time()</function>. It takes
    the event source object and a pointer to a variable to store the
    time in microseconds in.</para>

    <para><function>sd_event_source_set_time()</function> changes the
    configured time value of a timer event source created previously
    with <function>sd_event_add_time()</function>. It takes the event
    source object and a time relative to the selected clock's
    epoch, in microseconds.</para>

    <para><function>sd_event_source_get_time_accuracy()</function>
    retrieves the configured accuracy value of a timer event source
    created previously with <function>sd_event_add_time()</function>. It
    takes the event source object and a pointer to a variable to store
    the accuracy in microseconds in.</para>

    <para><function>sd_event_source_set_time_accuracy()</function>
    changes the configured accuracy of a timer event source created
    previously with <function>sd_event_add_time()</function>. It takes
    the event source object and an accuracy, in microseconds.</para>

    <para><function>sd_event_source_get_time_clock()</function>
    retrieves the configured clock of a timer event source created
    previously with <function>sd_event_add_time()</function>. It takes
    the event source object and a pointer to a variable to store the
    clock identifier in.</para>

  </refsect1>

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

    <para>On success, these functions return 0 or a positive
    integer. On failure, they return a negative errno-style error
    code. </para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

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

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

        <listitem><para>Not enough memory to allocate an object.</para></listitem>
      </varlistentry>

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

        <listitem><para>An invalid argument has been passed.</para></listitem>

      </varlistentry>

      <varlistentry>
        <term><constant>-ESTALE</constant></term>

        <listitem><para>The event loop is already terminated.</para></listitem>

      </varlistentry>

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

        <listitem><para>The event loop has been created in a different process.</para></listitem>

      </varlistentry>

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

        <listitem><para>The selected clock is not supported by the event loop implementation.</para></listitem>

      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para><function>sd_event_add_time()</function> and the other functions
    described here are available as a shared library, which can be
    compiled and linked to with the
    <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    file.</para>
  </refsect1>

  <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_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
