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