<?xml version='1.0'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <refentry id="sd_bus_slot_ref" xmlns:xi="http://www.w3.org/2001/XInclude"> <refentryinfo> <title>sd_bus_slot_ref</title> <productname>systemd</productname> </refentryinfo> <refmeta> <refentrytitle>sd_bus_slot_ref</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_bus_slot_ref</refname> <refname>sd_bus_slot_unref</refname> <refname>sd_bus_slot_unrefp</refname> <refpurpose>Create and destroy references to a bus slot object</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> <funcprototype> <funcdef>sd_bus_slot *<function>sd_bus_slot_ref</function></funcdef> <paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>sd_bus_slot *<function>sd_bus_slot_unref</function></funcdef> <paramdef>sd_bus_slot *<parameter>slot</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>void <function>sd_bus_slot_unrefp</function></funcdef> <paramdef>sd_bus_slot **<parameter>slotp</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_bus_slot_ref()</function> increases the internal reference counter of <parameter>slot</parameter> by one.</para> <para><function>sd_bus_slot_unref()</function> decreases the internal reference counter of <parameter>slot</parameter> by one. Once the reference count has dropped to zero, slot object is destroyed and cannot be used anymore, so further calls to <function>sd_bus_slot_ref()</function> or <function>sd_bus_slot_unref()</function> are illegal.</para> <para><function>sd_bus_slot_unrefp()</function> is similar to <function>sd_bus_slot_unref()</function> but takes a pointer to a pointer to an <type>sd_bus_slot</type> object. This call is useful in conjunction with GCC's and LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable Attribute</ulink>. See <citerefentry><refentrytitle>sd_bus_new</refentrytitle><manvolnum>3</manvolnum></citerefentry> for an example how to use the cleanup attribute.</para> <para><function>sd_bus_slot_ref()</function> and <function>sd_bus_slot_unref()</function> execute no operation if the passed in bus object address is <constant>NULL</constant>. <function>sd_bus_slot_unrefp()</function> will first dereference its argument, which must not be <constant>NULL</constant>, and will execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>.</para> </refsect1> <refsect1> <title>Return Value</title> <para><function>sd_bus_slot_ref()</function> always returns the argument.</para> <para><function>sd_bus_slot_unref()</function> always returns <constant>NULL</constant>.</para> </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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_message_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_call_method_async</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>