1 <?xml version='
1.0'
?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
6 SPDX-License-Identifier: LGPL-2.1+
8 This file is part of systemd.
10 Copyright 2014 Lennart Poettering
12 systemd is free software; you can redistribute it and/or modify it
13 under the terms of the GNU Lesser General Public License as published by
14 the Free Software Foundation; either version 2.1 of the License, or
15 (at your option) any later version.
17 systemd is distributed in the hope that it will be useful, but
18 WITHOUT ANY WARRANTY; without even the implied warranty of
19 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
20 Lesser General Public License for more details.
22 You should have received a copy of the GNU Lesser General Public License
23 along with systemd; If not, see <http://www.gnu.org/licenses/>.
26 <refentry id=
"sd_event_new" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
29 <title>sd_event_new
</title>
30 <productname>systemd
</productname>
34 <contrib>Developer
</contrib>
35 <firstname>Lennart
</firstname>
36 <surname>Poettering
</surname>
37 <email>lennart@poettering.net
</email>
43 <refentrytitle>sd_event_new
</refentrytitle>
44 <manvolnum>3</manvolnum>
48 <refname>sd_event_new
</refname>
49 <refname>sd_event_default
</refname>
50 <refname>sd_event_ref
</refname>
51 <refname>sd_event_unref
</refname>
52 <refname>sd_event_unrefp
</refname>
53 <refname>sd_event_get_tid
</refname>
54 <refname>sd_event
</refname>
56 <refpurpose>Acquire and release an event loop object
</refpurpose>
61 <funcsynopsisinfo>#include
<systemd/sd-event.h
></funcsynopsisinfo>
63 <funcsynopsisinfo><token>typedef
</token> struct sd_event sd_event;
</funcsynopsisinfo>
66 <funcdef>int
<function>sd_event_new
</function></funcdef>
67 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
71 <funcdef>int
<function>sd_event_default
</function></funcdef>
72 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
76 <funcdef>sd_event *
<function>sd_event_ref
</function></funcdef>
77 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
81 <funcdef>sd_event *
<function>sd_event_unref
</function></funcdef>
82 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
86 <funcdef>void
<function>sd_event_unrefp
</function></funcdef>
87 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
91 <funcdef>int
<function>sd_event_get_tid
</function></funcdef>
92 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
93 <paramdef>pid_t *
<parameter>tid
</parameter></paramdef>
100 <title>Description
</title>
102 <para><function>sd_event_new()
</function> allocates a new event
103 loop object. The event loop object is returned in the
104 <parameter>event
</parameter> parameter. After use, drop
105 the returned reference with
106 <function>sd_event_unref()
</function>. When the last reference is
107 dropped, the object is freed.
</para>
109 <para><function>sd_event_default()
</function> acquires a reference
110 to the default event loop object of the calling thread, possibly
111 allocating a new object if no default event loop object has been
112 allocated yet for the thread. After use, drop the returned
113 reference with
<function>sd_event_unref()
</function>. When the
114 last reference is dropped, the event loop is freed. If this
115 function is called while the object returned from a previous call
116 from the same thread is still referenced, the same object is
117 returned again, but the reference is increased by one. It is
118 recommended to use this call instead of
119 <function>sd_event_new()
</function> in order to share event loop
120 objects between various components that are dispatched in the same
121 thread. All threads have exactly either zero or one default event loop
122 objects associated, but never more.
</para>
124 <para>After allocating an event loop object, add event sources to
126 <citerefentry><refentrytitle>sd_event_add_io
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
127 <citerefentry><refentrytitle>sd_event_add_time
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
128 <citerefentry><refentrytitle>sd_event_add_signal
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
129 <citerefentry><refentrytitle>sd_event_add_child
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
131 <citerefentry><refentrytitle>sd_event_add_defer
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
132 and then execute the event loop using
133 <citerefentry><refentrytitle>sd_event_run
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
135 <para><function>sd_event_ref()
</function> increases the reference
136 count of the specified event loop object by one.
</para>
138 <para><function>sd_event_unref()
</function> decreases the
139 reference count of the specified event loop object by one. If
140 the count hits zero, the object is freed. Note that it
141 is freed regardless of whether it is the default event loop object for a
142 thread or not. This means that allocating an event loop with
143 <function>sd_event_default()
</function>, then releasing it, and
144 then acquiring a new one with
145 <function>sd_event_default()
</function> will result in two
146 distinct objects. Note that, in order to free an event loop object,
147 all remaining event sources of the event loop also need to be
148 freed as each keeps a reference to it.
</para>
150 <para><function>sd_event_unrefp()
</function> is similar to
151 <function>sd_event_unref()
</function> but takes a pointer to a
152 pointer to an
<type>sd_event
</type> object. This call is useful in
153 conjunction with GCC's and LLVM's
<ulink
154 url=
"https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
155 Variable Attribute
</ulink>. Note that this function is defined as
156 inline function. Use a declaration like the following,
157 in order to allocate an event loop object that is freed
158 automatically as the code block is left:
</para>
161 __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
164 r = sd_event_default(
&event);
166 fprintf(stderr,
"Failed to allocate event loop: %s\n", strerror(-r));
170 <para><function>sd_event_ref()
</function>,
171 <function>sd_event_unref()
</function> and
172 <function>sd_event_unrefp()
</function> execute no operation if the
173 passed in event loop object is
<constant>NULL
</constant>.
</para>
175 <para><function>sd_event_get_tid()
</function> retrieves the thread
176 identifier (
"TID") of the thread the specified event loop object
177 is associated with. This call is only supported for event loops
178 allocated with
<function>sd_event_default()
</function>, and
179 returns the identifier for the thread the event loop is the
180 default event loop of. See
<citerefentry
181 project='man-pages'
><refentrytitle>gettid
</refentrytitle><manvolnum>2</manvolnum></citerefentry>
182 for more information on thread identifiers.
</para>
186 <title>Return Value
</title>
188 <para>On success,
<function>sd_event_new()
</function>,
189 <function>sd_event_default()
</function> and
190 <function>sd_event_get_tid()
</function> return
0 or a positive
191 integer. On failure, they return a negative errno-style error
192 code.
<function>sd_event_ref()
</function> always returns a pointer
193 to the event loop object passed
194 in.
<function>sd_event_unref()
</function> always returns
195 <constant>NULL
</constant>.
</para>
199 <title>Errors
</title>
201 <para>Returned errors may indicate the following problems:
</para>
205 <term><constant>-ENOMEM
</constant></term>
207 <listitem><para>Not enough memory to allocate the object.
</para></listitem>
211 <term><constant>-EMFILE
</constant></term>
213 <listitem><para>The maximum number of event loops has been allocated.
</para></listitem>
218 <term><constant>-ENXIO
</constant></term>
220 <listitem><para><function>sd_event_get_tid()
</function> was
221 invoked on an event loop object that was not allocated with
222 <function>sd_event_default()
</function>.
</para></listitem>
228 <xi:include href=
"libsystemd-pkgconfig.xml" />
231 <title>See Also
</title>
234 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
235 <citerefentry><refentrytitle>sd-event
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
236 <citerefentry><refentrytitle>sd_event_add_io
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
237 <citerefentry><refentrytitle>sd_event_add_time
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
238 <citerefentry><refentrytitle>sd_event_add_signal
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
239 <citerefentry><refentrytitle>sd_event_add_child
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
240 <citerefentry><refentrytitle>sd_event_add_defer
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
241 <citerefentry><refentrytitle>sd_event_add_post
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
242 <citerefentry><refentrytitle>sd_event_add_exit
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
243 <citerefentry><refentrytitle>sd_event_run
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
244 <citerefentry project='man-pages'
><refentrytitle>gettid
</refentrytitle><manvolnum>2</manvolnum></citerefentry>