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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<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 <systemd/sd-bus.h></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>
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