man/sd_bus_new.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_bus_new" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_bus_new</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_bus_new</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_bus_new</refname>
  20     <refname>sd_bus_ref</refname>
  21     <refname>sd_bus_unref</refname>
  22     <refname>sd_bus_unrefp</refname>
  23     <refname>sd_bus_close_unref</refname>
  24     <refname>sd_bus_close_unrefp</refname>
  25     <refname>sd_bus_flush_close_unref</refname>
  26     <refname>sd_bus_flush_close_unrefp</refname>
  27
  28     <refpurpose>Create a new bus object and create or destroy references to it</refpurpose>
  29   </refnamediv>
  30
  31   <refsynopsisdiv>
  32     <funcsynopsis>
  33       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  34
  35       <funcprototype>
  36         <funcdef>int <function>sd_bus_new</function></funcdef>
  37         <paramdef>sd_bus **<parameter>bus</parameter></paramdef>
  38       </funcprototype>
  39
  40       <funcprototype>
  41         <funcdef>sd_bus *<function>sd_bus_ref</function></funcdef>
  42         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  43       </funcprototype>
  44
  45       <funcprototype>
  46         <funcdef>sd_bus *<function>sd_bus_unref</function></funcdef>
  47         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>sd_bus *<function>sd_bus_close_unref</function></funcdef>
  52         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  53       </funcprototype>
  54
  55       <funcprototype>
  56         <funcdef>sd_bus *<function>sd_bus_flush_close_unref</function></funcdef>
  57         <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
  58       </funcprototype>
  59
  60       <funcprototype>
  61         <funcdef>void <function>sd_bus_unrefp</function></funcdef>
  62         <paramdef>sd_bus **<parameter>busp</parameter></paramdef>
  63       </funcprototype>
  64
  65       <funcprototype>
  66         <funcdef>void <function>sd_bus_close_unrefp</function></funcdef>
  67         <paramdef>sd_bus **<parameter>busp</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>void <function>sd_bus_flush_close_unrefp</function></funcdef>
  72         <paramdef>sd_bus **<parameter>busp</parameter></paramdef>
  73       </funcprototype>
  74     </funcsynopsis>
  75   </refsynopsisdiv>
  76
  77   <refsect1>
  78     <title>Description</title>
  79
  80     <para><function>sd_bus_new()</function> creates a new bus
  81     object. This object is reference-counted, and will be destroyed
  82     when all references are gone. Initially, the caller of this
  83     function owns the sole reference and the bus object will not be
  84     connected to any bus. To connect it to a bus, make sure
  85     to set an address with
  86     <citerefentry><refentrytitle>sd_bus_set_address</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  87     or a related call, and then start the connection with
  88     <citerefentry><refentrytitle>sd_bus_start</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  89
  90     <para>In most cases, it is better to use
  91     <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  92     <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  93     or related calls instead of the more low-level <function>sd_bus_new()</function> and
  94     <function>sd_bus_start()</function>. The higher-level functions not only allocate a bus object but also
  95     start the connection to a well-known bus in a single function call.</para>
  96
  97     <para><function>sd_bus_ref()</function> increases the reference
  98     counter of <parameter>bus</parameter> by one.</para>
  99
 100     <para><function>sd_bus_unref()</function> decreases the reference
 101     counter of <parameter>bus</parameter> by one. Once the reference
 102     count has dropped to zero, <parameter>bus</parameter> is destroyed
 103     and cannot be used anymore, so further calls to
 104     <function>sd_bus_ref()</function> or
 105     <function>sd_bus_unref()</function> are illegal.</para>
 106
 107     <para><function>sd_bus_unrefp()</function> is similar to
 108     <function>sd_bus_unref()</function> but takes a pointer to a
 109     pointer to an <type>sd_bus</type> object. This call is useful in
 110     conjunction with GCC's and LLVM's <ulink
 111     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 112     Variable Attribute</ulink>. Note that this function is defined as
 113     inline function. Use a declaration like the following, in order to
 114     allocate a bus object that is freed automatically as the code
 115     block is left:</para>
 116
 117     <programlisting>{
 118   __attribute__((cleanup(sd_bus_unrefp))) sd_bus *bus = NULL;
 119   int r;
 120   …
 121   r = sd_bus_default(&amp;bus);
 122   if (r &lt; 0)
 123     fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
 124   …
 125 }</programlisting>
 126
 127     <para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function>
 128     execute no operation if the passed in bus object address is
 129     <constant>NULL</constant>. <function>sd_bus_unrefp()</function> will first
 130     dereference its argument, which must not be <constant>NULL</constant>, and will
 131     execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>.
 132     </para>
 133
 134     <para><function>sd_bus_close_unref()</function> is similar to <function>sd_bus_unref()</function>, but
 135     first executes
 136     <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137     ensuring that the connection is terminated before the reference to the connection is dropped and possibly
 138     the object freed.</para>
 139
 140     <para><function>sd_bus_flush_close_unref()</function> is similar to <function>sd_bus_unref()</function>,
 141     but first executes
 142     <citerefentry><refentrytitle>sd_bus_flush</refentrytitle><manvolnum>3</manvolnum></citerefentry> as well
 143     as <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 144     ensuring that any pending messages are synchronously flushed out before the reference to the connection
 145     is dropped and possibly the object freed. This call is particularly useful immediately before exiting
 146     from a program as it ensures that any pending outgoing messages are written out, and unprocessed but
 147     queued incoming messages released before the connection is terminated and released.</para>
 148
 149     <para><function>sd_bus_close_unrefp()</function> is similar to
 150     <function>sd_bus_close_unref()</function>, but may be used in GCC's and LLVM's Clean-up Variable
 151     Attribute, see above. Similarly, <function>sd_bus_flush_close_unrefp()</function> is similar to
 152     <function>sd_bus_flush_close_unref()</function>.</para>
 153   </refsect1>
 154
 155   <refsect1>
 156     <title>Return Value</title>
 157
 158     <para>On success, <function>sd_bus_new()</function> returns 0 or a
 159     positive integer. On failure, it returns a negative errno-style
 160     error code.</para>
 161
 162     <para><function>sd_bus_ref()</function> always returns the argument.
 163     </para>
 164
 165     <para><function>sd_bus_unref()</function> and <function>sd_bus_flush_close_unref()</function> always return
 166     <constant>NULL</constant>.</para>
 167
 168     <refsect2>
 169       <title>Errors</title>
 170
 171       <para>Returned errors may indicate the following problems:</para>
 172
 173       <variablelist>
 174         <varlistentry>
 175           <term><constant>-ENOMEM</constant></term>
 176
 177           <listitem><para>Memory allocation failed.</para></listitem>
 178         </varlistentry>
 179       </variablelist>
 180     </refsect2>
 181   </refsect1>
 182
 183   <xi:include href="libsystemd-pkgconfig.xml" />
 184
 185   <refsect1>
 186     <title>See Also</title>
 187
 188     <para>
 189       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 190       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 191       <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 192       <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 193       <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 194       <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 195       <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 196     </para>
 197   </refsect1>
 198
 199 </refentry>