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+
9 <refentry id=
"sd_event_new" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
12 <title>sd_event_new
</title>
13 <productname>systemd
</productname>
17 <refentrytitle>sd_event_new
</refentrytitle>
18 <manvolnum>3</manvolnum>
22 <refname>sd_event_new
</refname>
23 <refname>sd_event_default
</refname>
24 <refname>sd_event_ref
</refname>
25 <refname>sd_event_unref
</refname>
26 <refname>sd_event_unrefp
</refname>
27 <refname>sd_event_get_tid
</refname>
28 <refname>sd_event
</refname>
30 <refpurpose>Acquire and release an event loop object
</refpurpose>
35 <funcsynopsisinfo>#include
<systemd/sd-event.h
></funcsynopsisinfo>
37 <funcsynopsisinfo><token>typedef
</token> struct sd_event sd_event;
</funcsynopsisinfo>
40 <funcdef>int
<function>sd_event_new
</function></funcdef>
41 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
45 <funcdef>int
<function>sd_event_default
</function></funcdef>
46 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
50 <funcdef>sd_event *
<function>sd_event_ref
</function></funcdef>
51 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
55 <funcdef>sd_event *
<function>sd_event_unref
</function></funcdef>
56 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
60 <funcdef>void
<function>sd_event_unrefp
</function></funcdef>
61 <paramdef>sd_event **
<parameter>event
</parameter></paramdef>
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>
74 <title>Description
</title>
76 <para><function>sd_event_new()
</function> allocates a new event
77 loop object. The event loop object is returned in the
78 <parameter>event
</parameter> parameter. After use, drop
79 the returned reference with
80 <function>sd_event_unref()
</function>. When the last reference is
81 dropped, the object is freed.
</para>
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
86 allocated yet for the thread. After use, drop the returned
87 reference with
<function>sd_event_unref()
</function>. When the
88 last reference is dropped, the event loop is freed. If this
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
95 thread. All threads have exactly either zero or one default event loop
96 objects associated, but never more.
</para>
98 <para>After allocating an event loop object, add event sources to
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>
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>
109 <para><function>sd_event_ref()
</function> increases the reference
110 count of the specified event loop object by one.
</para>
112 <para><function>sd_event_unref()
</function> decreases the
113 reference count of the specified event loop object by one. If
114 the count hits zero, the object is freed. Note that it
115 is freed regardless of whether it is the default event loop object for a
116 thread or not. This means that allocating an event loop with
117 <function>sd_event_default()
</function>, then releasing it, and
118 then acquiring a new one with
119 <function>sd_event_default()
</function> will result in two
120 distinct objects. Note that, in order to free an event loop object,
121 all remaining event sources of the event loop also need to be
122 freed as each keeps a reference to it.
</para>
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>
135 __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
138 r = sd_event_default(
&event);
140 fprintf(stderr,
"Failed to allocate event loop: %s\n", strerror(-r));
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
147 passed in event loop object is
<constant>NULL
</constant>.
</para>
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>
160 <title>Return Value
</title>
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
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
169 <constant>NULL
</constant>.
</para>
173 <title>Errors
</title>
175 <para>Returned errors may indicate the following problems:
</para>
179 <term><constant>-ENOMEM
</constant></term>
181 <listitem><para>Not enough memory to allocate the object.
</para></listitem>
185 <term><constant>-EMFILE
</constant></term>
187 <listitem><para>The maximum number of event loops has been allocated.
</para></listitem>
192 <term><constant>-ENXIO
</constant></term>
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>
202 <xi:include href=
"libsystemd-pkgconfig.xml" />
205 <title>See Also
</title>
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>,
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>