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"
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6 SPDX-License-Identifier: LGPL-2.1+
9 <refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
12 <title>sd_event_add_signal</title>
13 <productname>systemd</productname>
17 <contrib>More text</contrib>
18 <firstname>Zbigniew</firstname>
19 <surname>Jędrzejewski-Szmek</surname>
20 <email>zbyszek@in.waw.pl</email>
26 <refentrytitle>sd_event_add_signal</refentrytitle>
27 <manvolnum>3</manvolnum>
31 <refname>sd_event_add_signal</refname>
32 <refname>sd_event_source_get_signal</refname>
33 <refname>sd_event_signal_handler_t</refname>
35 <refpurpose>Add a UNIX process signal event source to an event
41 <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
43 <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
46 <funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
47 <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
48 <paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
49 <paramdef>void *<parameter>userdata</parameter></paramdef>
53 <funcdef>int <function>sd_event_add_signal</function></funcdef>
54 <paramdef>sd_event *<parameter>event</parameter></paramdef>
55 <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
56 <paramdef>int <parameter>signal</parameter></paramdef>
57 <paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
58 <paramdef>void *<parameter>userdata</parameter></paramdef>
62 <funcdef>int <function>sd_event_source_get_signal</function></funcdef>
63 <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
70 <title>Description</title>
72 <para><function>sd_event_add_signal()</function> adds a new UNIX
73 process signal event source to an event loop. The event loop
74 object is specified in the <parameter>event</parameter> parameter,
75 and the event source object is returned in the
76 <parameter>source</parameter> parameter. The
77 <parameter>signal</parameter> parameter specifies the numeric
78 signal to be handled (see <citerefentry
79 project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
80 The <parameter>handler</parameter> parameter must reference a
81 function to call when the signal is received or be
82 <constant>NULL</constant>. The handler function will be passed
83 the <parameter>userdata</parameter> pointer, which may be chosen
84 freely by the caller. The handler also receives a pointer to a
85 <structname>signalfd_siginfo</structname> structure containing
86 information about the received signal. See <citerefentry
87 project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
88 for further information.</para>
90 <para>Only a single handler may be installed for a specific
91 signal. The signal will be unblocked by this call, and must be
92 blocked before this function is called in all threads (using
94 project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
95 the handler is not specified (<parameter>handler</parameter> is
96 <constant>NULL</constant>), a default handler which causes the
97 program to exit cleanly will be used.</para>
99 <para>By default, the event source is enabled permanently
100 (<constant>SD_EVENT_ON</constant>), but this may be changed with
101 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
102 If the handler function returns a negative error code, it will be
103 disabled after the invocation, even if the
104 <constant>SD_EVENT_ON</constant> mode was requested before.
107 <para>To destroy an event source object use
108 <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
109 but note that the event source is only removed from the event loop
110 when all references to the event source are dropped. To make sure
111 an event source does not fire anymore, even if it is still referenced,
112 disable the event source using
113 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
114 with <constant>SD_EVENT_OFF</constant>.</para>
116 <para>If the second parameter of
117 <function>sd_event_add_signal()</function> is
118 <constant>NULL</constant> no reference to the event source object
119 is returned. In this case the event source is considered
120 "floating", and will be destroyed implicitly when the event loop
121 itself is destroyed.</para>
123 <para><function>sd_event_source_get_signal()</function> returns
124 the configured signal number of an event source created previously
125 with <function>sd_event_add_signal()</function>. It takes the
126 event source object as the <parameter>source</parameter>
131 <title>Return Value</title>
133 <para>On success, these functions return 0 or a positive
134 integer. On failure, they return a negative errno-style error
139 <title>Errors</title>
141 <para>Returned errors may indicate the following problems:</para>
145 <term><constant>-ENOMEM</constant></term>
147 <listitem><para>Not enough memory to allocate an object.</para></listitem>
151 <term><constant>-EINVAL</constant></term>
153 <listitem><para>An invalid argument has been passed.</para></listitem>
157 <term><constant>-EBUSY</constant></term>
159 <listitem><para>A handler is already installed for this
160 signal or the signal was not blocked previously.</para></listitem>
164 <term><constant>-ESTALE</constant></term>
166 <listitem><para>The event loop is already terminated.</para></listitem>
170 <term><constant>-ECHILD</constant></term>
172 <listitem><para>The event loop has been created in a different process.</para></listitem>
176 <term><constant>-EDOM</constant></term>
178 <listitem><para>The passed event source is not a signal event source.</para></listitem>
184 <xi:include href="libelogind-pkgconfig.xml" />
187 <title>See Also</title>
190 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
191 <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
192 <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
193 <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
194 <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
195 <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
196 <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
197 <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
198 <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
199 <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
200 <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
201 <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
202 <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
203 <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>