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 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
  81     <citerefentry
  82     project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>).</para>
  83
  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.
  90     </para>
  91
  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>
 100
 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>
 107
 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>
 113
 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>
 118     parameter.</para>
 119   </refsect1>
 120
 121   <refsect1>
 122     <title>Return Value</title>
 123
 124     <para>On success, these functions return 0 or a positive
 125     integer. On failure, they return a negative errno-style error
 126     code.</para>
 127
 128     <refsect2>
 129       <title>Errors</title>
 130
 131       <para>Returned errors may indicate the following problems:</para>
 132
 133       <variablelist>
 134         <varlistentry>
 135           <term><constant>-ENOMEM</constant></term>
 136
 137           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 138         </varlistentry>
 139
 140         <varlistentry>
 141           <term><constant>-EINVAL</constant></term>
 142
 143           <listitem><para>An invalid argument has been passed.</para></listitem>
 144         </varlistentry>
 145
 146         <varlistentry>
 147           <term><constant>-EBUSY</constant></term>
 148
 149           <listitem><para>A handler is already installed for this
 150           signal or the signal was not blocked previously.</para></listitem>
 151         </varlistentry>
 152
 153         <varlistentry>
 154           <term><constant>-ESTALE</constant></term>
 155
 156           <listitem><para>The event loop is already terminated.</para></listitem>
 157         </varlistentry>
 158
 159         <varlistentry>
 160           <term><constant>-ECHILD</constant></term>
 161
 162           <listitem><para>The event loop has been created in a different process.</para></listitem>
 163         </varlistentry>
 164
 165         <varlistentry>
 166           <term><constant>-EDOM</constant></term>
 167
 168           <listitem><para>The passed event source is not a signal event source.</para></listitem>
 169         </varlistentry>
 170
 171       </variablelist>
 172     </refsect2>
 173   </refsect1>
 174
 175   <xi:include href="libsystemd-pkgconfig.xml" />
 176
 177   <refsect1>
 178     <title>See Also</title>
 179
 180     <para>
 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>
 198     </para>
 199   </refsect1>
 200
 201 </refentry>