man/sd_event_add_signal.xml

   1 <?xml version='1.0'?>
   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+ -->
   5
   6 <refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_event_add_signal</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_event_add_signal</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_event_add_signal</refname>
  20     <refname>sd_event_source_get_signal</refname>
  21     <refname>sd_event_signal_handler_t</refname>
  22
  23     <refpurpose>Add a UNIX process signal event source to an event
  24     loop</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <funcsynopsis>
  29       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  30
  31       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  32
  33       <funcprototype>
  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>
  38       </funcprototype>
  39
  40       <funcprototype>
  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>
  47       </funcprototype>
  48
  49       <funcprototype>
  50         <funcdef>int <function>sd_event_source_get_signal</function></funcdef>
  51         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  52       </funcprototype>
  53
  54     </funcsynopsis>
  55   </refsynopsisdiv>
  56
  57   <refsect1>
  58     <title>Description</title>
  59
  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>
  77
  78     <para>Only a single handler may be installed for a specific
  79     signal. The signal will be unblocked by this call, and must be
  80     blocked before this function is called in all threads (using
  81     <citerefentry
  82     project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
  83     the handler is not specified (<parameter>handler</parameter> is
  84     <constant>NULL</constant>), a default handler which causes the
  85     program to exit cleanly will be used.</para>
  86
  87     <para>By default, the event source is enabled permanently
  88     (<constant>SD_EVENT_ON</constant>), but this may be changed with
  89     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  90     If the handler function returns a negative error code, it will be
  91     disabled after the invocation, even if the
  92     <constant>SD_EVENT_ON</constant> mode was requested before.
  93     </para>
  94
  95     <para>To destroy an event source object use
  96     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  97     but note that the event source is only removed from the event loop
  98     when all references to the event source are dropped. To make sure
  99     an event source does not fire anymore, even if it is still referenced,
 100     disable the event source using
 101     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 102     with <constant>SD_EVENT_OFF</constant>.</para>
 103
 104     <para>If the second parameter of
 105     <function>sd_event_add_signal()</function> is
 106     <constant>NULL</constant> no reference to the event source object
 107     is returned. In this case the event source is considered
 108     "floating", and will be destroyed implicitly when the event loop
 109     itself is destroyed.</para>
 110
 111     <para><function>sd_event_source_get_signal()</function> returns
 112     the configured signal number of an event source created previously
 113     with <function>sd_event_add_signal()</function>. It takes the
 114     event source object as the <parameter>source</parameter>
 115     parameter.</para>
 116   </refsect1>
 117
 118   <refsect1>
 119     <title>Return Value</title>
 120
 121     <para>On success, these functions return 0 or a positive
 122     integer. On failure, they return a negative errno-style error
 123     code.</para>
 124
 125     <refsect2>
 126       <title>Errors</title>
 127
 128       <para>Returned errors may indicate the following problems:</para>
 129
 130       <variablelist>
 131         <varlistentry>
 132           <term><constant>-ENOMEM</constant></term>
 133
 134           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 135         </varlistentry>
 136
 137         <varlistentry>
 138           <term><constant>-EINVAL</constant></term>
 139
 140           <listitem><para>An invalid argument has been passed.</para></listitem>
 141         </varlistentry>
 142
 143         <varlistentry>
 144           <term><constant>-EBUSY</constant></term>
 145
 146           <listitem><para>A handler is already installed for this
 147           signal or the signal was not blocked previously.</para></listitem>
 148         </varlistentry>
 149
 150         <varlistentry>
 151           <term><constant>-ESTALE</constant></term>
 152
 153           <listitem><para>The event loop is already terminated.</para></listitem>
 154         </varlistentry>
 155
 156         <varlistentry>
 157           <term><constant>-ECHILD</constant></term>
 158
 159           <listitem><para>The event loop has been created in a different process.</para></listitem>
 160         </varlistentry>
 161
 162         <varlistentry>
 163           <term><constant>-EDOM</constant></term>
 164
 165           <listitem><para>The passed event source is not a signal event source.</para></listitem>
 166         </varlistentry>
 167
 168       </variablelist>
 169     </refsect2>
 170   </refsect1>
 171
 172   <xi:include href="libsystemd-pkgconfig.xml" />
 173
 174   <refsect1>
 175     <title>See Also</title>
 176
 177     <para>
 178       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 179       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 180       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 181       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 182       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 184       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 185       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 186       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 187       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 188       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 189       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 190       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 191       <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 192     </para>
 193   </refsect1>
 194
 195 </refentry>