2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
6 <refentry id=
"sd_event_add_signal" xmlns:
xi=
"http://www.w3.org/2001/XInclude">
9 <title>sd_event_add_signal
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>sd_event_add_signal
</refentrytitle>
15 <manvolnum>3</manvolnum>
19 <refname>sd_event_add_signal
</refname>
20 <refname>sd_event_source_get_signal
</refname>
21 <refname>sd_event_signal_handler_t
</refname>
23 <refpurpose>Add a UNIX process signal event source to an event
29 <funcsynopsisinfo>#include
<systemd/sd-event.h
></funcsynopsisinfo>
31 <funcsynopsisinfo><token>typedef
</token> struct sd_event_source sd_event_source;
</funcsynopsisinfo>
34 <funcdef>typedef int (*
<function>sd_event_signal_handler_t
</function>)
</funcdef>
35 <paramdef>sd_event_source *
<parameter>s
</parameter></paramdef>
36 <paramdef>const struct signalfd_siginfo *
<parameter>si
</parameter></paramdef>
37 <paramdef>void *
<parameter>userdata
</parameter></paramdef>
41 <funcdef>int
<function>sd_event_add_signal
</function></funcdef>
42 <paramdef>sd_event *
<parameter>event
</parameter></paramdef>
43 <paramdef>sd_event_source **
<parameter>source
</parameter></paramdef>
44 <paramdef>int
<parameter>signal
</parameter></paramdef>
45 <paramdef>sd_event_signal_handler_t
<parameter>handler
</parameter></paramdef>
46 <paramdef>void *
<parameter>userdata
</parameter></paramdef>
50 <funcdef>int
<function>sd_event_source_get_signal
</function></funcdef>
51 <paramdef>sd_event_source *
<parameter>source
</parameter></paramdef>
58 <title>Description
</title>
60 <para><function>sd_event_add_signal()
</function> adds a new UNIX
61 process signal event source to an event loop. The event loop
62 object is specified in the
<parameter>event
</parameter> parameter,
63 and the event source object is returned in the
64 <parameter>source
</parameter> parameter. The
65 <parameter>signal
</parameter> parameter specifies the numeric
66 signal to be handled (see
<citerefentry
67 project='man-pages'
><refentrytitle>signal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
68 The
<parameter>handler
</parameter> parameter must reference a
69 function to call when the signal is received or be
70 <constant>NULL
</constant>. The handler function will be passed
71 the
<parameter>userdata
</parameter> pointer, which may be chosen
72 freely by the caller. The handler also receives a pointer to a
73 <structname>signalfd_siginfo
</structname> structure containing
74 information about the received signal. See
<citerefentry
75 project='man-pages'
><refentrytitle>signalfd
</refentrytitle><manvolnum>2</manvolnum></citerefentry>
76 for further information.
</para>
78 <para>Only a single handler may be installed for a specific signal. The signal must be blocked in all
79 threads before this function is called (using
<citerefentry
80 project='man-pages'
><refentrytitle>sigprocmask
</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
82 project='man-pages'
><refentrytitle>pthread_sigmask
</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
</para>
84 <para>By default, the event source is enabled permanently
85 (
<constant>SD_EVENT_ON
</constant>), but this may be changed with
86 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
87 If the handler function returns a negative error code, it will be
88 disabled after the invocation, even if the
89 <constant>SD_EVENT_ON
</constant> mode was requested before.
92 <para>To destroy an event source object use
93 <citerefentry><refentrytitle>sd_event_source_unref
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
94 but note that the event source is only removed from the event loop
95 when all references to the event source are dropped. To make sure
96 an event source does not fire anymore, even if it is still referenced,
97 disable the event source using
98 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>
99 with
<constant>SD_EVENT_OFF
</constant>.
</para>
101 <para>If the second parameter of
102 <function>sd_event_add_signal()
</function> is
103 <constant>NULL
</constant> no reference to the event source object
104 is returned. In this case the event source is considered
105 "floating", and will be destroyed implicitly when the event loop
106 itself is destroyed.
</para>
108 <para>If the
<parameter>handler
</parameter> parameter to
<function>sd_event_add_signal()
</function> is
109 <constant>NULL
</constant>, and the event source fires, this will be considered a request to exit the
110 event loop. In this case, the
<parameter>userdata
</parameter> parameter, cast to an integer, is passed as
111 the exit code parameter to
112 <citerefentry><refentrytitle>sd_event_exit
</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
114 <para><function>sd_event_source_get_signal()
</function> returns
115 the configured signal number of an event source created previously
116 with
<function>sd_event_add_signal()
</function>. It takes the
117 event source object as the
<parameter>source
</parameter>
122 <title>Return Value
</title>
124 <para>On success, these functions return
0 or a positive
125 integer. On failure, they return a negative errno-style error
129 <title>Errors
</title>
131 <para>Returned errors may indicate the following problems:
</para>
135 <term><constant>-ENOMEM
</constant></term>
137 <listitem><para>Not enough memory to allocate an object.
</para></listitem>
141 <term><constant>-EINVAL
</constant></term>
143 <listitem><para>An invalid argument has been passed.
</para></listitem>
147 <term><constant>-EBUSY
</constant></term>
149 <listitem><para>A handler is already installed for this
150 signal or the signal was not blocked previously.
</para></listitem>
154 <term><constant>-ESTALE
</constant></term>
156 <listitem><para>The event loop is already terminated.
</para></listitem>
160 <term><constant>-ECHILD
</constant></term>
162 <listitem><para>The event loop has been created in a different process.
</para></listitem>
166 <term><constant>-EDOM
</constant></term>
168 <listitem><para>The passed event source is not a signal event source.
</para></listitem>
175 <xi:include href=
"libsystemd-pkgconfig.xml" />
178 <title>See Also
</title>
181 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
182 <citerefentry><refentrytitle>sd-event
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
183 <citerefentry><refentrytitle>sd_event_new
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
184 <citerefentry><refentrytitle>sd_event_now
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
185 <citerefentry><refentrytitle>sd_event_add_io
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
186 <citerefentry><refentrytitle>sd_event_add_time
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
187 <citerefentry><refentrytitle>sd_event_add_child
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
188 <citerefentry><refentrytitle>sd_event_add_inotify
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
189 <citerefentry><refentrytitle>sd_event_add_defer
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
190 <citerefentry><refentrytitle>sd_event_source_set_enabled
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
191 <citerefentry><refentrytitle>sd_event_source_set_description
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
192 <citerefentry><refentrytitle>sd_event_source_set_userdata
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
193 <citerefentry><refentrytitle>sd_event_source_set_floating
</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
194 <citerefentry project='man-pages'
><refentrytitle>signal
</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
195 <citerefentry project='man-pages'
><refentrytitle>signalfd
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
196 <citerefentry project='man-pages'
><refentrytitle>sigprocmask
</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
197 <citerefentry project='man-pages'
><refentrytitle>pthread_sigmask
</refentrytitle><manvolnum>3</manvolnum></citerefentry>