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<refentry id="sd_event_add_time" xmlns:xi="http://www.w3.org/2001/XInclude">

  <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>
    <refname>sd_event_time_handler_t</refname>

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

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

      <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>

      <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_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>int <function>sd_event_source_get_time</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>uint64_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>uint64_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>uint64_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>uint64_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. The event loop object is specified
    in the <parameter>event</parameter> parameter, the event source
    object 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>,
    <constant>CLOCK_BOOTTIME</constant>,
    <constant>CLOCK_REALTIME_ALARM</constant> or
    <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 (µs), relative to the clock's epoch, specifying when
    the timer shall elapse the earliest. If a time that already lies
    in the past is specified (including 0), the timer source is
    dispatched immediately in the next event loop iterations. The
    <parameter>accuracy</parameter> parameter takes an additional
    accuracy value in µs specifying a time the timer event may be
    delayed. Specify 0 for selecting the default accuracy
    (250ms). Specify 1µs for most accurate timers. Consider specifying
    60000000µs or larger (1min) 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> 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. To query the actual time the
    handler was called use
    <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</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 the
    <constant>SD_EVENT_ON</constant> mode was requested before. Note
    that a timer event set to <constant>SD_EVENT_ON</constant> will
    fire continuously unless its configured time is updated using
    <function>sd_event_source_set_time()</function>.
    </para>

    <para>To destroy an event source object use
    <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    but note that the event source is only removed from the event loop
    when all references to the event source are dropped. To make sure
    an event source does not fire anymore, even when there's still a
    reference to it kept, consider setting the event source to
    <constant>SD_EVENT_OFF</constant> with
    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>If the second parameter of
    <function>sd_event_add_time()</function> is passed as NULL no
    reference to the event source object is returned. In this case the
    event source is considered "floating", and will be destroyed
    implicitly when the event loop itself is destroyed.</para>

    <para>If the <parameter>handler</parameter> to
    <function>sd_event_add_time()</function> is passed as NULL, and
    the event source fires, this will be considered a request to exit
    the event loop. In this case, the <parameter>userdata</parameter>
    parameter, cast to an integer is used for the exit code passed to
    <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>Use <constant>CLOCK_BOOTTIME_ALARM</constant> and
    <constant>CLOCK_REALTIME_ALARM</constant> to define event sources
    that may wake up the system from suspend.</para>

    <para>In order to set up relative timers (that is, relative to the
    current time), retrieve the current time via
    <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    add the desired timespan to sleep to it, and pass the result as
    the <parameter>usec</parameter> parameter to
    <function>sd_event_add_time()</function>.</para>

    <para>In order to set up repetitive timers (that is, timers that
    are triggered in regular intervals), set up the timer normally,
    for the first invocation. Each time the event handler is invoked,
    update the timer's trigger time with
    <citerefentry><refentrytitle>sd_event_source_set_time</refentrytitle><manvolnum>3</manvolnum></citerefentry> for the next timer
    iteration, and reenable the timer using
    <function>sd_event_source_set_enabled()</function>. To calculate
    the next point in time to pass to
    <function>sd_event_source_set_time()</function>, either use as
    base the <parameter>usec</parameter> parameter passed to the timer
    callback, or the timestamp returned by
    <function>sd_event_now()</function>. In the former case timer
    events will be regular, while in the latter case the scheduling
    latency will keep accumulating on the timer.</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, relative to the selected clock's epoch, in µs 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 µs.</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 µs 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 µs.</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>

      <varlistentry>
        <term><constant>-EDOM</constant></term>

        <listitem><para>The passed event source is not a timer event source.</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_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_add_io</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>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>timerfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
