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 a better idea to invoke
  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
  94     <function>sd_bus_new()</function> and
  95     <function>sd_bus_start()</function>. The higher-level calls not
  96     only allocate a bus object but also start the connection to a
  97     well-known bus in a single function invocation.</para>
  98
  99     <para><function>sd_bus_ref()</function> increases the reference
 100     counter of <parameter>bus</parameter> by one.</para>
 101
 102     <para><function>sd_bus_unref()</function> decreases the reference
 103     counter of <parameter>bus</parameter> by one. Once the reference
 104     count has dropped to zero, <parameter>bus</parameter> is destroyed
 105     and cannot be used anymore, so further calls to
 106     <function>sd_bus_ref()</function> or
 107     <function>sd_bus_unref()</function> are illegal.</para>
 108
 109     <para><function>sd_bus_unrefp()</function> is similar to
 110     <function>sd_bus_unref()</function> but takes a pointer to a
 111     pointer to an <type>sd_bus</type> object. This call is useful in
 112     conjunction with GCC's and LLVM's <ulink
 113     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 114     Variable Attribute</ulink>. Note that this function is defined as
 115     inline function. Use a declaration like the following, in order to
 116     allocate a bus object that is freed automatically as the code
 117     block is left:</para>
 118
 119     <programlisting>{
 120   __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
 121   int r;
 122   …
 123   r = sd_bus_default(&amp;bus);
 124   if (r &lt; 0)
 125     fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
 126   …
 127 }</programlisting>
 128
 129     <para><function>sd_bus_ref()</function> and <function>sd_bus_unref()</function>
 130     execute no operation if the passed in bus object address is
 131     <constant>NULL</constant>. <function>sd_bus_unrefp()</function> will first
 132     dereference its argument, which must not be <constant>NULL</constant>, and will
 133     execute no operation if <emphasis>that</emphasis> is <constant>NULL</constant>.
 134     </para>
 135
 136     <para><function>sd_bus_close_unref()</function> is similar to <function>sd_bus_unref()</function>, but
 137     first executes
 138     <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 139     ensuring that the connection is terminated before the reference to the connection is dropped and possibly
 140     the object freed.</para>
 141
 142     <para><function>sd_bus_flush_close_unref()</function> is similar to <function>sd_bus_unref()</function>,
 143     but first executes
 144     <citerefentry><refentrytitle>sd_bus_flush</refentrytitle><manvolnum>3</manvolnum></citerefentry> as well
 145     as <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 146     ensuring that any pending messages are synchronously flushed out before the reference to the connection
 147     is dropped and possibly the object freed. This call is particularly useful immediately before exiting
 148     from a program as it ensures that any pending outgoing messages are written out, and unprocessed but
 149     queued incoming messages released before the connection is terminated and released.</para>
 150
 151     <para><function>sd_bus_close_unrefp()</function> is similar to
 152     <function>sd_bus_close_unref()</function>, but may be used in GCC's and LLVM's Clean-up Variable
 153     Attribute, see above. Similarly, <function>sd_bus_flush_close_unrefp()</function> is similar to
 154     <function>sd_bus_flush_close_unref()</function>.</para>
 155   </refsect1>
 156
 157   <refsect1>
 158     <title>Return Value</title>
 159
 160     <para>On success, <function>sd_bus_new()</function> returns 0 or a
 161     positive integer. On failure, it returns a negative errno-style
 162     error code.</para>
 163
 164     <para><function>sd_bus_ref()</function> always returns the argument.
 165     </para>
 166
 167     <para><function>sd_bus_unref()</function> and <function>sd_bus_flush_close_unref()</function> always return
 168     <constant>NULL</constant>.</para>
 169
 170     <refsect2>
 171       <title>Errors</title>
 172
 173       <para>Returned errors may indicate the following problems:</para>
 174
 175       <variablelist>
 176         <varlistentry>
 177           <term><constant>-ENOMEM</constant></term>
 178
 179           <listitem><para>Memory allocation failed.</para></listitem>
 180         </varlistentry>
 181       </variablelist>
 182     </refsect2>
 183   </refsect1>
 184
 185   <xi:include href="libsystemd-pkgconfig.xml" />
 186
 187   <refsect1>
 188     <title>See Also</title>
 189
 190     <para>
 191       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 192       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 193       <citerefentry><refentrytitle>sd_bus_default_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 194       <citerefentry><refentrytitle>sd_bus_default_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 195       <citerefentry><refentrytitle>sd_bus_open_user</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 196       <citerefentry><refentrytitle>sd_bus_open_system</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 197       <citerefentry><refentrytitle>sd_bus_close</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 198     </para>
 199   </refsect1>
 200
 201 </refentry>