systemd/man/sd_event_source_set_destroy_callback.xml

<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

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

  <refentryinfo>
    <title>sd_event_source_set_destroy_callback</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_event_source_set_destroy_callback</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_source_set_destroy_callback</refname>
    <refname>sd_event_source_get_destroy_callback</refname>
    <refname>sd_event_destroy_t</refname>

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

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

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

      <funcprototype>
        <funcdef>int <function>sd_event_source_set_destroy_callback</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>sd_event_destroy_t <parameter>callback</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_destroy_callback</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>sd_event_destroy_t *<parameter>callback</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_source_set_destroy_callback()</function> sets <parameter>callback</parameter> as the
    callback function to be called right before the event source object <parameter>source</parameter> is
    deallocated. The <parameter>userdata</parameter> pointer from the event source 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_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, or directly,
    see
    <citerefentry><refentrytitle>sd_event_source_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 event source object itself is already invalidated, and executing
    operations or taking new references to the event source object is not permissible.</para>

    <para><function>sd_event_source_get_destroy_callback()</function> returns the current callback
    for <parameter>source</parameter> in the <parameter>callback</parameter> parameter.</para>
  </refsect1>

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

    <para>On success, <function>sd_event_source_set_destroy_callback()</function> returns 0 or a positive
    integer. On failure, it returns a negative errno-style error code.</para>

    <para><function>sd_event_source_get_destroy_callback()</function> returns positive if the destroy
    callback function is set, 0 if not. On failure, returns a negative errno-style error code.</para>

    <refsect2>
      <title>Errors</title>

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

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

          <listitem><para>The <parameter>source</parameter> parameter is <constant>NULL</constant>.
          </para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

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

  <refsect1>
    <title>History</title>
    <para><function>sd_event_destroy_t()</function>,
    <function>sd_event_source_set_destroy_callback()</function>, and
    <function>sd_event_source_get_destroy_callback()</function> were added in version 239.</para>
  </refsect1>

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

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>