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514094f9 | 1 | <?xml version='1.0'?> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
7d6b2723 | 9 | <refentry id="sd_bus_track_new" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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10 | |
11 | <refentryinfo> | |
12 | <title>sd_bus_track_new</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_bus_track_new</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_bus_track_new</refname> | |
23 | <refname>sd_bus_track_ref</refname> | |
24 | <refname>sd_bus_track_unref</refname> | |
25 | <refname>sd_bus_track_unrefp</refname> | |
26 | <refname>sd_bus_track_set_recursive</refname> | |
27 | <refname>sd_bus_track_get_recursive</refname> | |
28 | <refname>sd_bus_track_get_bus</refname> | |
29 | <refname>sd_bus_track_get_userdata</refname> | |
30 | <refname>sd_bus_track_set_userdata</refname> | |
31 | ||
32 | <refpurpose>Track bus peers</refpurpose> | |
33 | </refnamediv> | |
34 | ||
35 | <refsynopsisdiv> | |
36 | <funcsynopsis> | |
37 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
38 | ||
39 | <funcprototype> | |
40 | <funcdef>int <function>sd_bus_track_new</function></funcdef> | |
41 | <paramdef>sd_bus* <parameter>bus</parameter></paramdef> | |
42 | <paramdef>sd_bus_track** <parameter>ret</parameter></paramdef> | |
43 | <paramdef>sd_bus_track_handler_t <parameter>handler</parameter></paramdef> | |
44 | <paramdef>void* <parameter>userdata</parameter></paramdef> | |
45 | </funcprototype> | |
46 | ||
47 | <funcprototype> | |
48 | <funcdef>sd_bus_track *<function>sd_bus_track_ref</function></funcdef> | |
49 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
50 | </funcprototype> | |
51 | ||
52 | <funcprototype> | |
53 | <funcdef>sd_bus_track *<function>sd_bus_track_unref</function></funcdef> | |
54 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
55 | </funcprototype> | |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>void <function>sd_bus_track_unrefp</function></funcdef> | |
59 | <paramdef>sd_bus_track **<parameter>t</parameter></paramdef> | |
60 | </funcprototype> | |
61 | ||
62 | <funcprototype> | |
63 | <funcdef>int <function>sd_bus_track_get_recursive</function></funcdef> | |
64 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
65 | </funcprototype> | |
66 | ||
67 | <funcprototype> | |
68 | <funcdef>int <function>sd_bus_track_set_recursive</function></funcdef> | |
69 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
70 | <paramdef>int <parameter>b</parameter></paramdef> | |
71 | </funcprototype> | |
72 | ||
73 | <funcprototype> | |
74 | <funcdef>sd_bus* <function>sd_bus_track_get_bus</function></funcdef> | |
75 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
76 | </funcprototype> | |
77 | ||
78 | <funcprototype> | |
79 | <funcdef>void* <function>sd_bus_track_get_userdata</function></funcdef> | |
80 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
81 | </funcprototype> | |
82 | ||
83 | <funcprototype> | |
84 | <funcdef>void* <function>sd_bus_track_set_userdata</function></funcdef> | |
85 | <paramdef>sd_bus_track *<parameter>t</parameter></paramdef> | |
86 | <paramdef>void *userdata</paramdef> | |
87 | </funcprototype> | |
88 | ||
89 | </funcsynopsis> | |
90 | </refsynopsisdiv> | |
91 | ||
92 | <refsect1> | |
93 | <title>Description</title> | |
94 | ||
95 | <para><function>sd_bus_track_new()</function> creates a new bus peer tracking object. The object is allocated for | |
96 | the specified bus, and returned in the <parameter>*ret</parameter> parameter. After use, the object should be freed | |
97 | again by dropping the acquired reference with <function>sd_bus_track_unref()</function> (see below). A bus peer | |
98 | tracking object may be used to keep track of peers on a specific IPC bus, for cases where peers are making use of | |
99 | one or more local objects, in order to control the lifecycle of the local objects and ensure they stay around as | |
100 | long as the peers needing them are around, and unreferenced (and possibly destroyed) as soon as all relevant peers | |
101 | have vanished. Each bus peer tracking object may be used to track zero, one or more peers add a time. References to | |
102 | specific bus peers are added via | |
103 | <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> or | |
104 | <function>sd_bus_track_add_sender()</function>. They may be dropped again via | |
105 | <function>sd_bus_track_remove_name()</function> and | |
106 | <function>sd_bus_track_remove_sender()</function>. Alternatively, references on peers are removed automatically | |
107 | when they disconnect from the bus. If non-NULL the <parameter>handler</parameter> may specify a function that is | |
108 | invoked whenever the last reference is dropped, regardless whether the reference is dropped explicitly via | |
109 | <function>sd_bus_track_remove_name()</function> or implicitly because the peer disconnected from the bus. The final | |
110 | argument <parameter>userdata</parameter> may be used to attach a generic user data pointer to the object. This | |
111 | pointer is passed to the handler callback when it is invoked.</para> | |
112 | ||
113 | <para><function>sd_bus_track_ref()</function> creates a new reference to a bus peer tracking object. This object | |
114 | will not be destroyed until <function>sd_bus_track_unref()</function> has been called as many times plus once | |
115 | more. Once the reference count has dropped to zero, the specified object cannot be used anymore, further calls to | |
116 | <function>sd_bus_track_ref()</function> or <function>sd_bus_track_unref()</function> on the same object are | |
117 | illegal.</para> | |
118 | ||
119 | <para><function>sd_bus_track_unref()</function> destroys a reference to a bus peer tracking object.</para> | |
120 | ||
121 | <para><function>sd_bus_track_unrefp()</function> is similar to <function>sd_bus_track_unref()</function> but takes | |
122 | a pointer to a pointer to an <type>sd_bus_track</type> object. This call is useful in conjunction with GCC's and | |
123 | LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable | |
124 | Attribute</ulink>. Note that this function is defined as inline function.</para> | |
125 | ||
126 | <para><function>sd_bus_track_ref()</function>, <function>sd_bus_track_unref()</function> and | |
127 | <function>sd_bus_track_unrefp()</function> execute no operation if the passed in bus peer tracking object is | |
128 | <constant>NULL</constant>.</para> | |
129 | ||
130 | <para>Bus peer tracking objects may exist in two modes: by default they operate in non-recursive mode, but may | |
131 | optionally be switched into recursive mode. If operating in the default non-recursive mode a peer is either tracked | |
132 | or not tracked. In this mode invoking <function>sd_bus_track_add_name()</function> multiple times in a row for the | |
133 | same peer is fully equivalent to calling it just once, as the call adds the peer to the set of tracked peers if | |
134 | necessary, and executes no operation if the peer is already being tracked. A single invocation of | |
135 | <function>sd_bus_track_remove_name()</function> removes the reference on the peer again, regardless how many times | |
136 | <function>sd_bus_track_add_name()</function> was called before. If operating in recursive mode, the number of times | |
137 | <function>sd_bus_track_add_name()</function> is invoked for the same peer name is counted and | |
138 | <function>sd_bus_track_remove_name()</function> must be called the same number of times before the peer is not | |
139 | tracked anymore, with the exception when the tracked peer vanishes from the bus, in which case the count is | |
140 | irrelevant and the tracking of the specific peer is immediately | |
141 | removed. <function>sd_bus_track_get_recursive()</function> may be used to determine whether the bus peer tracking | |
142 | object is operating in recursive mode. <function>sd_bus_track_set_recursive()</function> may be used to enable or | |
143 | disable recursive mode. By default a bus peer tracking object operates in non-recursive mode, and | |
144 | <function>sd_bus_track_get_recursive()</function> for a newly allocated object hence returns a value equal to | |
145 | zero. Use <function>sd_bus_track_set_recursive()</function> to enable recursive mode, right after allocation. It | |
146 | takes a boolean argument to enable or disable recursive mode. Note that tracking objects for which | |
147 | <function>sd_bus_track_add_name()</function> was already invoked at least once (and which hence track already one | |
148 | or more peers) may not be switched from recursive to non-recursive mode anymore.</para> | |
149 | ||
150 | <para><function>sd_bus_track_get_bus()</function> returns the bus object the bus peer tracking object belongs | |
151 | to. It returns the bus object initially passed to <function>sd_bus_track_new()</function> when the object was | |
152 | allocated.</para> | |
153 | ||
154 | <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer set on the bus peer | |
155 | tracking object at the time of creation using <function>sd_bus_track_new()</function> or at a later time, using | |
156 | <function>sd_bus_track_set_userdata()</function>.</para> | |
157 | </refsect1> | |
158 | ||
159 | <refsect1> | |
160 | <title>Return Value</title> | |
161 | ||
162 | <para>On success, <function>sd_bus_track_new()</function> and <function>sd_bus_track_set_recursive()</function> | |
163 | return 0 or a positive integer. On failure, they return a negative errno-style error code.</para> | |
164 | ||
165 | <para><function>sd_bus_track_ref()</function> always returns the argument.</para> | |
166 | ||
167 | <para><function>sd_bus_track_unref()</function> always returns <constant>NULL</constant>.</para> | |
168 | ||
169 | <para><function>sd_bus_track_get_recursive()</function> returns 0 if non-recursive mode is selected (default), and | |
170 | greater than 0 if recursive mode is selected. On failure a negative errno-style error code is returned.</para> | |
171 | ||
172 | <para><function>sd_bus_track_get_bus()</function> returns the bus object associated to the bus peer tracking | |
173 | object.</para> | |
174 | ||
175 | <para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer associated with the | |
176 | bus peer tracking object. <function>sd_bus_track_set_userdata()</function> returns the previous user data pointer | |
177 | set.</para> | |
178 | ||
179 | </refsect1> | |
180 | ||
181 | <refsect1> | |
182 | <title>Reference ownership</title> | |
183 | ||
184 | <para>The <function>sd_bus_track_new()</function> function creates a new object and the caller owns the sole | |
185 | reference. When not needed anymore, this reference should be destroyed with | |
186 | <function>sd_bus_track_unref()</function>. | |
187 | </para> | |
188 | </refsect1> | |
189 | ||
190 | <refsect1> | |
191 | <title>Errors</title> | |
192 | ||
193 | <para>Returned errors may indicate the following problems:</para> | |
194 | ||
195 | <variablelist> | |
196 | ||
197 | <varlistentry> | |
198 | <term><constant>-EBUSY</constant></term> | |
199 | ||
200 | <listitem><para>Bus peers have already been added to the bus peer tracking object and | |
201 | <function>sd_bus_track_set_recursive()</function> was called to change tracking mode.</para></listitem> | |
202 | </varlistentry> | |
203 | ||
204 | <varlistentry> | |
205 | <term><constant>-EINVAL</constant></term> | |
206 | ||
207 | <listitem><para>Specified parameter is invalid | |
208 | (<constant>NULL</constant> in case of output | |
209 | parameters).</para></listitem> | |
210 | </varlistentry> | |
211 | ||
212 | <varlistentry> | |
213 | <term><constant>-ENOMEM</constant></term> | |
214 | ||
215 | <listitem><para>Memory allocation failed.</para></listitem> | |
216 | </varlistentry> | |
217 | ||
218 | </variablelist> | |
219 | </refsect1> | |
220 | ||
7d6b2723 | 221 | <xi:include href="libsystemd-pkgconfig.xml" /> |
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222 | |
223 | <refsect1> | |
224 | <title>See Also</title> | |
225 | ||
226 | <para> | |
227 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
228 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
229 | <citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
230 | </para> | |
231 | </refsect1> | |
232 | ||
233 | </refentry> |