-<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<?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">
<!--
- This file is part of systemd.
-
- Copyright 2014 Zbigniew Jędrzejewski-Szmek
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
+ SPDX-License-Identifier: LGPL-2.1+
-->
-<refentry id="sd_bus_new">
+<refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_new</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>A monkey with a typewriter</contrib>
- <firstname>Zbigniew</firstname>
- <surname>Jędrzejewski-Szmek</surname>
- <email>zbyszek@in.waw.pl</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
<refname>sd_bus_new</refname>
<refname>sd_bus_ref</refname>
<refname>sd_bus_unref</refname>
+ <refname>sd_bus_unrefp</refname>
<refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
</refnamediv>
<funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
</funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_bus_unrefp</function></funcdef>
+ <paramdef>sd_bus **<parameter>busp</parameter></paramdef>
+ </funcprototype>
</funcsynopsis>
</refsynopsisdiv>
or a related call, and then start the connection with
<citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
- <para>In most cases it's a better idea to invoke
+ <para>In most cases, it is a better idea to invoke
<citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or related calls instead of the more low-level
only allocate a bus object but also start the connection to a
well-known bus in a single function invocation.</para>
- <para><function>sd_bus_ref()</function> creates a new reference to
- <parameter>bus</parameter>.</para>
+ <para><function>sd_bus_ref()</function> increases the reference
+ counter of <parameter>bus</parameter> by one.</para>
- <para><function>sd_bus_unref()</function> destroys a reference to
- <parameter>bus</parameter>. Once the reference count has dropped
- to zero, <parameter>bus</parameter> cannot be used anymore, so
- further calls to <function>sd_bus_ref()</function> or
+ <para><function>sd_bus_unref()</function> decreases the reference
+ counter of <parameter>bus</parameter> by one. Once the reference
+ count has dropped to zero, <parameter>bus</parameter> is destroyed
+ and cannot be used anymore, so further calls to
+ <function>sd_bus_ref()</function> or
<function>sd_bus_unref()</function> are illegal.</para>
+
+ <para><function>sd_bus_unrefp()</function> is similar to
+ <function>sd_bus_unref()</function> but takes a pointer to a
+ pointer to an <type>sd_bus</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>. Note that this function is defined as
+ inline function. Use a declaration like the following, in order to
+ allocate a bus object that is freed automatically as the code
+ block is left:</para>
+
+ <programlisting>{
+ __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
+ int r;
+ …
+ r = sd_bus_default(&bus);
+ if (r < 0)
+ fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
+ …
+}</programlisting>
+
+ <para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function>
+ execute no operation if the passed in bus object address is
+ <constant>NULL</constant>. <function>sd_bus_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>
positive integer. On failure, it returns a negative errno-style
error code.</para>
- <para><function>sd_bus_ref</function> always returns the argument.
+ <para><function>sd_bus_ref()</function> always returns the argument.
</para>
- <para><function>sd_bus_unref</function> always returns
+ <para><function>sd_bus_unref()</function> always returns
<constant>NULL</constant>.</para>
</refsect1>
</variablelist>
</refsect1>
- <refsect1>
- <title>Notes</title>
-
- <para><function>sd_bus_new()</function> and other functions
- described here 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>
+ <xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>See Also</title>
projects / thirdparty / systemd.git / blobdiff