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 Copyright © 2014 Zbigniew Jędrzejewski-Szmek
11 <refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
14 <title>sd_event_add_signal</title>
15 <productname>systemd</productname>
19 <contrib>More text</contrib>
20 <firstname>Zbigniew</firstname>
21 <surname>Jędrzejewski-Szmek</surname>
22 <email>zbyszek@in.waw.pl</email>
28 <refentrytitle>sd_event_add_signal</refentrytitle>
29 <manvolnum>3</manvolnum>
33 <refname>sd_event_add_signal</refname>
34 <refname>sd_event_source_get_signal</refname>
35 <refname>sd_event_signal_handler_t</refname>
37 <refpurpose>Add a UNIX process signal event source to an event
43 <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
45 <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
48 <funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
49 <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
50 <paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
51 <paramdef>void *<parameter>userdata</parameter></paramdef>
55 <funcdef>int <function>sd_event_add_signal</function></funcdef>
56 <paramdef>sd_event *<parameter>event</parameter></paramdef>
57 <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
58 <paramdef>int <parameter>signal</parameter></paramdef>
59 <paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
60 <paramdef>void *<parameter>userdata</parameter></paramdef>
64 <funcdef>int <function>sd_event_source_get_signal</function></funcdef>
65 <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
72 <title>Description</title>
74 <para><function>sd_event_add_signal()</function> adds a new UNIX
75 process signal event source to an event loop. The event loop
76 object is specified in the <parameter>event</parameter> parameter,
77 and the event source object is returned in the
78 <parameter>source</parameter> parameter. The
79 <parameter>signal</parameter> parameter specifies the numeric
80 signal to be handled (see <citerefentry
81 project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
82 The <parameter>handler</parameter> parameter must reference a
83 function to call when the signal is received or be
84 <constant>NULL</constant>. The handler function will be passed
85 the <parameter>userdata</parameter> pointer, which may be chosen
86 freely by the caller. The handler also receives a pointer to a
87 <structname>signalfd_siginfo</structname> structure containing
88 information about the received signal. See <citerefentry
89 project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
90 for further information.</para>
92 <para>Only a single handler may be installed for a specific
93 signal. The signal will be unblocked by this call, and must be
94 blocked before this function is called in all threads (using
96 project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
97 the handler is not specified (<parameter>handler</parameter> is
98 <constant>NULL</constant>), a default handler which causes the
99 program to exit cleanly will be used.</para>
101 <para>By default, the event source is enabled permanently
102 (<constant>SD_EVENT_ON</constant>), but this may be changed with
103 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
104 If the handler function returns a negative error code, it will be
105 disabled after the invocation, even if the
106 <constant>SD_EVENT_ON</constant> mode was requested before.
109 <para>To destroy an event source object use
110 <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
111 but note that the event source is only removed from the event loop
112 when all references to the event source are dropped. To make sure
113 an event source does not fire anymore, even if it is still referenced,
114 disable the event source using
115 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
116 with <constant>SD_EVENT_OFF</constant>.</para>
118 <para>If the second parameter of
119 <function>sd_event_add_signal()</function> is
120 <constant>NULL</constant> no reference to the event source object
121 is returned. In this case the event source is considered
122 "floating", and will be destroyed implicitly when the event loop
123 itself is destroyed.</para>
125 <para><function>sd_event_source_get_signal()</function> returns
126 the configured signal number of an event source created previously
127 with <function>sd_event_add_signal()</function>. It takes the
128 event source object as the <parameter>source</parameter>
133 <title>Return Value</title>
135 <para>On success, these functions return 0 or a positive
136 integer. On failure, they return a negative errno-style error
141 <title>Errors</title>
143 <para>Returned errors may indicate the following problems:</para>
147 <term><constant>-ENOMEM</constant></term>
149 <listitem><para>Not enough memory to allocate an object.</para></listitem>
153 <term><constant>-EINVAL</constant></term>
155 <listitem><para>An invalid argument has been passed.</para></listitem>
159 <term><constant>-EBUSY</constant></term>
161 <listitem><para>A handler is already installed for this
162 signal or the signal was not blocked previously.</para></listitem>
166 <term><constant>-ESTALE</constant></term>
168 <listitem><para>The event loop is already terminated.</para></listitem>
172 <term><constant>-ECHILD</constant></term>
174 <listitem><para>The event loop has been created in a different process.</para></listitem>
178 <term><constant>-EDOM</constant></term>
180 <listitem><para>The passed event source is not a signal event source.</para></listitem>
186 <xi:include href="libelogind-pkgconfig.xml" />
189 <title>See Also</title>
192 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
193 <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
194 <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
195 <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
196 <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
197 <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
198 <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
199 <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
200 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
201 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
202 <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
203 <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
204 <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
205 <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>