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514094f9 | 1 | <?xml version='1.0'?> |
faae655d | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
dc83f27a | 9 | <refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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10 | |
11 | <refentryinfo> | |
12 | <title>sd_event_new</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_event_new</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_event_new</refname> | |
23 | <refname>sd_event_default</refname> | |
24 | <refname>sd_event_ref</refname> | |
25 | <refname>sd_event_unref</refname> | |
4afd3348 | 26 | <refname>sd_event_unrefp</refname> |
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27 | <refname>sd_event_get_tid</refname> |
28 | <refname>sd_event</refname> | |
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29 | |
30 | <refpurpose>Acquire and release an event loop object</refpurpose> | |
31 | </refnamediv> | |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
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35 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
36 | ||
37 | <funcsynopsisinfo><token>typedef</token> struct sd_event sd_event;</funcsynopsisinfo> | |
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38 | |
39 | <funcprototype> | |
40 | <funcdef>int <function>sd_event_new</function></funcdef> | |
dc83f27a | 41 | <paramdef>sd_event **<parameter>event</parameter></paramdef> |
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42 | </funcprototype> |
43 | ||
44 | <funcprototype> | |
45 | <funcdef>int <function>sd_event_default</function></funcdef> | |
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46 | <paramdef>sd_event **<parameter>event</parameter></paramdef> |
47 | </funcprototype> | |
48 | ||
49 | <funcprototype> | |
50 | <funcdef>sd_event *<function>sd_event_ref</function></funcdef> | |
51 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
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52 | </funcprototype> |
53 | ||
54 | <funcprototype> | |
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55 | <funcdef>sd_event *<function>sd_event_unref</function></funcdef> |
56 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
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57 | </funcprototype> |
58 | ||
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59 | <funcprototype> |
60 | <funcdef>void <function>sd_event_unrefp</function></funcdef> | |
61 | <paramdef>sd_event **<parameter>event</parameter></paramdef> | |
62 | </funcprototype> | |
63 | ||
faae655d | 64 | <funcprototype> |
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65 | <funcdef>int <function>sd_event_get_tid</function></funcdef> |
66 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
67 | <paramdef>pid_t *<parameter>tid</parameter></paramdef> | |
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68 | </funcprototype> |
69 | ||
70 | </funcsynopsis> | |
71 | </refsynopsisdiv> | |
72 | ||
73 | <refsect1> | |
74 | <title>Description</title> | |
75 | ||
76 | <para><function>sd_event_new()</function> allocates a new event | |
77 | loop object. The event loop object is returned in the | |
b8bde116 | 78 | <parameter>event</parameter> parameter. After use, drop |
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79 | the returned reference with |
80 | <function>sd_event_unref()</function>. When the last reference is | |
bfe6c07e | 81 | dropped, the object is freed.</para> |
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82 | |
83 | <para><function>sd_event_default()</function> acquires a reference | |
84 | to the default event loop object of the calling thread, possibly | |
85 | allocating a new object if no default event loop object has been | |
b8bde116 | 86 | allocated yet for the thread. After use, drop the returned |
a6ad1458 | 87 | reference with <function>sd_event_unref()</function>. When the |
b8bde116 | 88 | last reference is dropped, the event loop is freed. If this |
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89 | function is called while the object returned from a previous call |
90 | from the same thread is still referenced, the same object is | |
91 | returned again, but the reference is increased by one. It is | |
92 | recommended to use this call instead of | |
93 | <function>sd_event_new()</function> in order to share event loop | |
94 | objects between various components that are dispatched in the same | |
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95 | thread. All threads have exactly either zero or one default event loop |
96 | objects associated, but never more.</para> | |
faae655d | 97 | |
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98 | <para>After allocating an event loop object, add event sources to |
99 | it with | |
100 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
101 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
102 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
103 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
104 | or | |
105 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
106 | and then execute the event loop using | |
107 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
108 | ||
faae655d | 109 | <para><function>sd_event_ref()</function> increases the reference |
bfe6c07e | 110 | count of the specified event loop object by one.</para> |
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111 | |
112 | <para><function>sd_event_unref()</function> decreases the | |
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113 | reference count of the specified event loop object by one. If |
114 | the count hits zero, the object is freed. Note that it | |
dca348bc | 115 | is freed regardless of whether it is the default event loop object for a |
faae655d | 116 | thread or not. This means that allocating an event loop with |
b8bde116 | 117 | <function>sd_event_default()</function>, then releasing it, and |
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118 | then acquiring a new one with |
119 | <function>sd_event_default()</function> will result in two | |
b938cb90 | 120 | distinct objects. Note that, in order to free an event loop object, |
faae655d | 121 | all remaining event sources of the event loop also need to be |
bfe6c07e | 122 | freed as each keeps a reference to it.</para> |
dc83f27a | 123 | |
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124 | <para><function>sd_event_unrefp()</function> is similar to |
125 | <function>sd_event_unref()</function> but takes a pointer to a | |
126 | pointer to an <type>sd_event</type> object. This call is useful in | |
127 | conjunction with GCC's and LLVM's <ulink | |
128 | url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up | |
129 | Variable Attribute</ulink>. Note that this function is defined as | |
130 | inline function. Use a declaration like the following, | |
131 | in order to allocate an event loop object that is freed | |
132 | automatically as the code block is left:</para> | |
133 | ||
134 | <programlisting>{ | |
135 | __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL; | |
136 | int r; | |
137 | … | |
138 | r = sd_event_default(&event); | |
139 | if (r < 0) | |
140 | fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r)); | |
141 | … | |
142 | }</programlisting> | |
143 | ||
144 | <para><function>sd_event_ref()</function>, | |
145 | <function>sd_event_unref()</function> and | |
146 | <function>sd_event_unrefp()</function> execute no operation if the | |
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147 | passed in event loop object is <constant>NULL</constant>.</para> |
148 | ||
149 | <para><function>sd_event_get_tid()</function> retrieves the thread | |
150 | identifier ("TID") of the thread the specified event loop object | |
151 | is associated with. This call is only supported for event loops | |
152 | allocated with <function>sd_event_default()</function>, and | |
153 | returns the identifier for the thread the event loop is the | |
154 | default event loop of. See <citerefentry | |
155 | project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
156 | for more information on thread identifiers.</para> | |
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157 | </refsect1> |
158 | ||
159 | <refsect1> | |
160 | <title>Return Value</title> | |
161 | ||
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162 | <para>On success, <function>sd_event_new()</function>, |
163 | <function>sd_event_default()</function> and | |
164 | <function>sd_event_get_tid()</function> return 0 or a positive | |
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165 | integer. On failure, they return a negative errno-style error |
166 | code. <function>sd_event_ref()</function> always returns a pointer | |
167 | to the event loop object passed | |
168 | in. <function>sd_event_unref()</function> always returns | |
bfe6c07e | 169 | <constant>NULL</constant>.</para> |
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170 | </refsect1> |
171 | ||
172 | <refsect1> | |
173 | <title>Errors</title> | |
174 | ||
175 | <para>Returned errors may indicate the following problems:</para> | |
176 | ||
177 | <variablelist> | |
178 | <varlistentry> | |
8474b70c | 179 | <term><constant>-ENOMEM</constant></term> |
faae655d | 180 | |
bfe6c07e | 181 | <listitem><para>Not enough memory to allocate the object.</para></listitem> |
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182 | </varlistentry> |
183 | ||
184 | <varlistentry> | |
8474b70c | 185 | <term><constant>-EMFILE</constant></term> |
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186 | |
187 | <listitem><para>The maximum number of event loops has been allocated.</para></listitem> | |
188 | ||
189 | </varlistentry> | |
faae655d | 190 | |
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191 | <varlistentry> |
192 | <term><constant>-ENXIO</constant></term> | |
faae655d | 193 | |
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194 | <listitem><para><function>sd_event_get_tid()</function> was |
195 | invoked on an event loop object that was not allocated with | |
196 | <function>sd_event_default()</function>.</para></listitem> | |
197 | </varlistentry> | |
198 | ||
199 | </variablelist> | |
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200 | </refsect1> |
201 | ||
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202 | <xi:include href="libsystemd-pkgconfig.xml" /> |
203 | ||
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204 | <refsect1> |
205 | <title>See Also</title> | |
206 | ||
207 | <para> | |
208 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
209 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
210 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
211 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
212 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
213 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
214 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
215 | <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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216 | <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
217 | <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
218 | <citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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219 | </para> |
220 | </refsect1> | |
221 | ||
222 | </refentry> |