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>). If
  83     the handler is not specified (<parameter>handler</parameter> is <constant>NULL</constant>), a default
  84     handler which causes the program to exit cleanly will be used.</para>
  85
  86     <para>By default, the event source is enabled permanently
  87     (<constant>SD_EVENT_ON</constant>), but this may be changed with
  88     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  89     If the handler function returns a negative error code, it will be
  90     disabled after the invocation, even if the
  91     <constant>SD_EVENT_ON</constant> mode was requested before.
  92     </para>
  93
  94     <para>To destroy an event source object use
  95     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  96     but note that the event source is only removed from the event loop
  97     when all references to the event source are dropped. To make sure
  98     an event source does not fire anymore, even if it is still referenced,
  99     disable the event source using
 100     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 101     with <constant>SD_EVENT_OFF</constant>.</para>
 102
 103     <para>If the second parameter of
 104     <function>sd_event_add_signal()</function> is
 105     <constant>NULL</constant> no reference to the event source object
 106     is returned. In this case the event source is considered
 107     "floating", and will be destroyed implicitly when the event loop
 108     itself is destroyed.</para>
 109
 110     <para><function>sd_event_source_get_signal()</function> returns
 111     the configured signal number of an event source created previously
 112     with <function>sd_event_add_signal()</function>. It takes the
 113     event source object as the <parameter>source</parameter>
 114     parameter.</para>
 115   </refsect1>
 116
 117   <refsect1>
 118     <title>Return Value</title>
 119
 120     <para>On success, these functions return 0 or a positive
 121     integer. On failure, they return a negative errno-style error
 122     code.</para>
 123
 124     <refsect2>
 125       <title>Errors</title>
 126
 127       <para>Returned errors may indicate the following problems:</para>
 128
 129       <variablelist>
 130         <varlistentry>
 131           <term><constant>-ENOMEM</constant></term>
 132
 133           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 134         </varlistentry>
 135
 136         <varlistentry>
 137           <term><constant>-EINVAL</constant></term>
 138
 139           <listitem><para>An invalid argument has been passed.</para></listitem>
 140         </varlistentry>
 141
 142         <varlistentry>
 143           <term><constant>-EBUSY</constant></term>
 144
 145           <listitem><para>A handler is already installed for this
 146           signal or the signal was not blocked previously.</para></listitem>
 147         </varlistentry>
 148
 149         <varlistentry>
 150           <term><constant>-ESTALE</constant></term>
 151
 152           <listitem><para>The event loop is already terminated.</para></listitem>
 153         </varlistentry>
 154
 155         <varlistentry>
 156           <term><constant>-ECHILD</constant></term>
 157
 158           <listitem><para>The event loop has been created in a different process.</para></listitem>
 159         </varlistentry>
 160
 161         <varlistentry>
 162           <term><constant>-EDOM</constant></term>
 163
 164           <listitem><para>The passed event source is not a signal event source.</para></listitem>
 165         </varlistentry>
 166
 167       </variablelist>
 168     </refsect2>
 169   </refsect1>
 170
 171   <xi:include href="libsystemd-pkgconfig.xml" />
 172
 173   <refsect1>
 174     <title>See Also</title>
 175
 176     <para>
 177       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 178       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 179       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 180       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 181       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 182       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 184       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 185       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 186       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 187       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 188       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 189       <citerefentry><refentrytitle>sd_event_source_set_floating</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       <citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 193       <citerefentry project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 194     </para>
 195   </refsect1>
 196
 197 </refentry>