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

  <refentryinfo>
    <title>sd_bus_slot_set_destroy_callback</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_bus_slot_set_destroy_callback</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_bus_slot_set_destroy_callback</refname>
    <refname>sd_bus_slot_get_destroy_callback</refname>
    <refname>sd_bus_track_set_destroy_callback</refname>
    <refname>sd_bus_track_get_destroy_callback</refname>
    <refname>sd_bus_destroy_t</refname>

    <refpurpose>Define the callback function for resource cleanup.</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>typedef int (*<function>sd_bus_destroy_t</function>)</funcdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_slot_set_destroy_callback</function></funcdef>
        <paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
        <paramdef>sd_bus_destroy_t <parameter>callback</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_slot_get_destroy_callback</function></funcdef>
        <paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef>
        <paramdef>sd_bus_destroy_t *<parameter>callback</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_track_set_destroy_callback</function></funcdef>
        <paramdef>sd_bus_track *<parameter>track</parameter></paramdef>
        <paramdef>sd_bus_destroy_t <parameter>callback</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_bus_track_get_destroy_callback</function></funcdef>
        <paramdef>sd_bus_track *<parameter>track</parameter></paramdef>
        <paramdef>sd_bus_destroy_t *<parameter>callback</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_bus_slot_set_destroy_callback()</function> sets <parameter>callback</parameter> as the callback
    function to be called right before the bus slot object <parameter>slot</parameter> is deallocated. The
    <parameter>userdata</parameter> pointer from the slot object will be passed as the <parameter>userdata</parameter>
    parameter. This pointer can be set by an argument to the constructor functions, see
    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>, or directly,
    see <citerefentry><refentrytitle>sd_bus_slot_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    This callback function is called even if <parameter>userdata</parameter> is <constant>NULL</constant>. Note that
    this callback is invoked at a time where the bus slot object itself is already invalidated, and executing
    operations or taking new references to the bus slot object is not permissible.</para>

    <para><function>sd_bus_slot_get_destroy_callback()</function> returns the current callback
    for <parameter>slot</parameter> in the <parameter>callback</parameter> parameter.</para>

    <para><function>sd_bus_track_set_destroy_callback()</function> and
    <function>sd_bus_track_get_destroy_callback</function> provide equivalent functionality for the
    <parameter>userdata</parameter> pointer associated with bus peer tracking objects. For details about bus peer
    tracking objects, see
    <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  </refsect1>

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

    <para>On success, <function>sd_bus_slot_set_destroy_callback()</function> and
    <function>sd_bus_track_set_destroy_callback()</function> return 0 or a positive integer. On failure, they return a
    negative errno-style error code.</para>

    <para><function>sd_bus_slot_get_destroy_callback()</function> and
    <function>sd_bus_track_get_destroy_callback</function> return positive if the destroy callback function is set, 0
    if not. 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>-EINVAL</constant></term>

        <listitem><para>The <parameter>slot</parameter> or <parameter>track</parameter> parameter is
        <constant>NULL</constant>.</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-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_slot_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_bus_track_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>