systemd/man/sd_bus_message_get_monotonic_usec.xml

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<refentry id="sd_bus_message_get_monotonic_usec">

  <refentryinfo>
    <title>sd_bus_message_get_monotonic_usec</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_bus_message_get_monotonic_usec</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_message_get_monotonic_usec</refname>
    <refname>sd_bus_message_get_realtime_usec</refname>
    <refname>sd_bus_message_get_seqnum</refname>
    <refpurpose>Retrieve the sender timestamps and sequence number of a message</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>int <function>sd_bus_message_get_monotonic_usec</function></funcdef>
        <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_message_get_realtime_usec</function></funcdef>
        <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
        <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_message_get_seqnum</function></funcdef>
        <paramdef>sd_bus_message *<parameter>message</parameter></paramdef>
        <paramdef>uint64_t *<parameter>seqnum</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_message_get_monotonic_usec()</function>
    returns the monotonic timestamp of the time the message was sent.
    This value is in microseconds since the
    <constant>CLOCK_MONOTONIC</constant> epoch, see
    <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    for details.</para>

    <para>Similarly,
    <function>sd_bus_message_get_realtime_usec()</function> returns
    the realtime (wallclock) timestamp of the time the message was
    sent. This value is in microseconds since Jan 1st, 1970, i.e. in
    the <constant>CLOCK_REALTIME</constant> clock.</para>

    <para><function>sd_bus_message_get_seqnum()</function> returns the
    kernel-assigned sequence number of the message. The kernel assigns
    a global, monotonically increasing sequence number to all messages
    transmitted on the local system, at the time the message was sent.
    This sequence number is useful for determining message send order,
    even across different buses of the local system. The sequence
    number combined with the boot ID of the system (as returned by
    <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
    is a suitable globally unique identifier for bus messages.</para>

    <para>Note that the sending order and receiving order of messages
    might differ, in particular for broadcast messages. This means
    that the sequence number and the timestamps of messages a client
    reads are not necessarily monotonically increasing.</para>

    <para>These timestamps and the sequence number are attached to
    each message by the kernel and cannot be manipulated by the
    sender.</para>

    <para>Note that these timestamps are only available on some bus
    transports, and only after support for them has been negotiated
    with the
    <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call.</para>
  </refsect1>

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

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

    <para>On success, the timestamp or sequence number is returned in
    the specified 64-bit unsigned integer variable.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

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

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

        <listitem><para>A specified parameter is
        invalid.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ENODATA</constant></term>

        <listitem><para>No timestamp or sequence number information is
        attached to the passed message. This error is returned if the
        underlying transport does not support timestamping or
        assigning of sequence numbers, or if this feature has not been
        negotiated with
        <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>The
    <function>sd_bus_message_get_monotonic_usec()</function>,
    <function>sd_bus_message_get_realtime_usec()</function>, and
    <function>sd_bus_message_get_seqnum()</function> interfaces 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-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_negotiate_timestamp</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>