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514094f9 | 1 | <?xml version='1.0'?> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
faae655d | 5 | |
dc83f27a | 6 | <refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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7 | |
8 | <refentryinfo> | |
9 | <title>sd_event_new</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_event_new</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_event_new</refname> | |
20 | <refname>sd_event_default</refname> | |
21 | <refname>sd_event_ref</refname> | |
22 | <refname>sd_event_unref</refname> | |
4afd3348 | 23 | <refname>sd_event_unrefp</refname> |
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24 | <refname>sd_event_get_tid</refname> |
25 | <refname>sd_event</refname> | |
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26 | |
27 | <refpurpose>Acquire and release an event loop object</refpurpose> | |
28 | </refnamediv> | |
29 | ||
30 | <refsynopsisdiv> | |
31 | <funcsynopsis> | |
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32 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
33 | ||
34 | <funcsynopsisinfo><token>typedef</token> struct sd_event sd_event;</funcsynopsisinfo> | |
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35 | |
36 | <funcprototype> | |
37 | <funcdef>int <function>sd_event_new</function></funcdef> | |
dc83f27a | 38 | <paramdef>sd_event **<parameter>event</parameter></paramdef> |
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39 | </funcprototype> |
40 | ||
41 | <funcprototype> | |
42 | <funcdef>int <function>sd_event_default</function></funcdef> | |
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43 | <paramdef>sd_event **<parameter>event</parameter></paramdef> |
44 | </funcprototype> | |
45 | ||
46 | <funcprototype> | |
47 | <funcdef>sd_event *<function>sd_event_ref</function></funcdef> | |
48 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
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49 | </funcprototype> |
50 | ||
51 | <funcprototype> | |
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52 | <funcdef>sd_event *<function>sd_event_unref</function></funcdef> |
53 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
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54 | </funcprototype> |
55 | ||
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56 | <funcprototype> |
57 | <funcdef>void <function>sd_event_unrefp</function></funcdef> | |
58 | <paramdef>sd_event **<parameter>event</parameter></paramdef> | |
59 | </funcprototype> | |
60 | ||
faae655d | 61 | <funcprototype> |
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62 | <funcdef>int <function>sd_event_get_tid</function></funcdef> |
63 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
64 | <paramdef>pid_t *<parameter>tid</parameter></paramdef> | |
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65 | </funcprototype> |
66 | ||
67 | </funcsynopsis> | |
68 | </refsynopsisdiv> | |
69 | ||
70 | <refsect1> | |
71 | <title>Description</title> | |
72 | ||
73 | <para><function>sd_event_new()</function> allocates a new event | |
74 | loop object. The event loop object is returned in the | |
b8bde116 | 75 | <parameter>event</parameter> parameter. After use, drop |
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76 | the returned reference with |
77 | <function>sd_event_unref()</function>. When the last reference is | |
bfe6c07e | 78 | dropped, the object is freed.</para> |
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79 | |
80 | <para><function>sd_event_default()</function> acquires a reference | |
81 | to the default event loop object of the calling thread, possibly | |
82 | allocating a new object if no default event loop object has been | |
b8bde116 | 83 | allocated yet for the thread. After use, drop the returned |
a6ad1458 | 84 | reference with <function>sd_event_unref()</function>. When the |
b8bde116 | 85 | last reference is dropped, the event loop is freed. If this |
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86 | function is called while the object returned from a previous call |
87 | from the same thread is still referenced, the same object is | |
88 | returned again, but the reference is increased by one. It is | |
89 | recommended to use this call instead of | |
90 | <function>sd_event_new()</function> in order to share event loop | |
91 | objects between various components that are dispatched in the same | |
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92 | thread. All threads have exactly either zero or one default event loop |
93 | objects associated, but never more.</para> | |
faae655d | 94 | |
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95 | <para>After allocating an event loop object, add event sources to |
96 | it with | |
97 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
98 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
99 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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100 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
101 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
dc83f27a | 102 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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103 | <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry> or |
104 | <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
dc83f27a | 105 | and then execute the event loop using |
8274a30d | 106 | <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> |
dc83f27a | 107 | |
faae655d | 108 | <para><function>sd_event_ref()</function> increases the reference |
bfe6c07e | 109 | count of the specified event loop object by one.</para> |
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110 | |
111 | <para><function>sd_event_unref()</function> decreases the | |
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112 | reference count of the specified event loop object by one. If |
113 | the count hits zero, the object is freed. Note that it | |
dca348bc | 114 | is freed regardless of whether it is the default event loop object for a |
faae655d | 115 | thread or not. This means that allocating an event loop with |
b8bde116 | 116 | <function>sd_event_default()</function>, then releasing it, and |
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117 | then acquiring a new one with |
118 | <function>sd_event_default()</function> will result in two | |
b938cb90 | 119 | distinct objects. Note that, in order to free an event loop object, |
faae655d | 120 | all remaining event sources of the event loop also need to be |
bfe6c07e | 121 | freed as each keeps a reference to it.</para> |
dc83f27a | 122 | |
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123 | <para><function>sd_event_unrefp()</function> is similar to |
124 | <function>sd_event_unref()</function> but takes a pointer to a | |
125 | pointer to an <type>sd_event</type> object. This call is useful in | |
126 | conjunction with GCC's and LLVM's <ulink | |
127 | url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up | |
128 | Variable Attribute</ulink>. Note that this function is defined as | |
129 | inline function. Use a declaration like the following, | |
130 | in order to allocate an event loop object that is freed | |
131 | automatically as the code block is left:</para> | |
132 | ||
133 | <programlisting>{ | |
134 | __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL; | |
135 | int r; | |
136 | … | |
137 | r = sd_event_default(&event); | |
138 | if (r < 0) | |
139 | fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r)); | |
140 | … | |
141 | }</programlisting> | |
142 | ||
143 | <para><function>sd_event_ref()</function>, | |
144 | <function>sd_event_unref()</function> and | |
145 | <function>sd_event_unrefp()</function> execute no operation if the | |
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146 | passed in event loop object is <constant>NULL</constant>.</para> |
147 | ||
148 | <para><function>sd_event_get_tid()</function> retrieves the thread | |
149 | identifier ("TID") of the thread the specified event loop object | |
150 | is associated with. This call is only supported for event loops | |
151 | allocated with <function>sd_event_default()</function>, and | |
152 | returns the identifier for the thread the event loop is the | |
153 | default event loop of. See <citerefentry | |
154 | project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
155 | for more information on thread identifiers.</para> | |
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156 | </refsect1> |
157 | ||
158 | <refsect1> | |
159 | <title>Return Value</title> | |
160 | ||
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161 | <para>On success, <function>sd_event_new()</function>, <function>sd_event_default()</function> and |
162 | <function>sd_event_get_tid()</function> return 0 or a positive integer. On failure, they return a | |
163 | negative errno-style error code. <function>sd_event_ref()</function> always returns a pointer to the | |
164 | event loop object passed in. <function>sd_event_unref()</function> always returns | |
bfe6c07e | 165 | <constant>NULL</constant>.</para> |
faae655d | 166 | |
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167 | <refsect2> |
168 | <title>Errors</title> | |
faae655d | 169 | |
b1de39de | 170 | <para>Returned errors may indicate the following problems:</para> |
faae655d | 171 | |
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172 | <variablelist> |
173 | <varlistentry> | |
174 | <term><constant>-ENOMEM</constant></term> | |
faae655d | 175 | |
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176 | <listitem><para>Not enough memory to allocate the object.</para></listitem> |
177 | </varlistentry> | |
faae655d | 178 | |
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179 | <varlistentry> |
180 | <term><constant>-EMFILE</constant></term> | |
faae655d | 181 | |
b1de39de | 182 | <listitem><para>The maximum number of event loops has been allocated.</para></listitem> |
faae655d | 183 | |
b1de39de | 184 | </varlistentry> |
faae655d | 185 | |
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186 | <varlistentry> |
187 | <term><constant>-ENXIO</constant></term> | |
faae655d | 188 | |
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189 | <listitem><para><function>sd_event_get_tid()</function> was invoked on an event loop object that |
190 | was not allocated with <function>sd_event_default()</function>.</para></listitem> | |
191 | </varlistentry> | |
dc83f27a | 192 | |
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193 | </variablelist> |
194 | </refsect2> | |
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195 | </refsect1> |
196 | ||
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197 | <xi:include href="libsystemd-pkgconfig.xml" /> |
198 | ||
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199 | <refsect1> |
200 | <title>See Also</title> | |
201 | ||
202 | <para> | |
203 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
204 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
207 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8274a30d | 209 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
faae655d | 210 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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211 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
212 | <citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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213 | </para> |
214 | </refsect1> | |
215 | ||
216 | </refentry> |