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-or-later -->
   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     <refname>SD_EVENT_SIGNAL_PROCMASK</refname>
  23
  24     <refpurpose>Add a UNIX process signal event source to an event
  25     loop</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  31
  32       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  33
  34       <funcsynopsisinfo><constant>SD_EVENT_SIGNAL_PROCMASK</constant></funcsynopsisinfo>
  35
  36       <funcprototype>
  37         <funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
  38         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  39         <paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
  40         <paramdef>void *<parameter>userdata</parameter></paramdef>
  41       </funcprototype>
  42
  43       <funcprototype>
  44         <funcdef>int <function>sd_event_add_signal</function></funcdef>
  45         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  46         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  47         <paramdef>int <parameter>signal</parameter></paramdef>
  48         <paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
  49         <paramdef>void *<parameter>userdata</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_event_source_get_signal</function></funcdef>
  54         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  55       </funcprototype>
  56     </funcsynopsis>
  57   </refsynopsisdiv>
  58
  59   <refsect1>
  60     <title>Description</title>
  61
  62     <para><function>sd_event_add_signal()</function> adds a new UNIX process signal event source to an event
  63     loop. The event loop object is specified in the <parameter>event</parameter> parameter, and the event
  64     source object is returned in the <parameter>source</parameter> parameter. The
  65     <parameter>signal</parameter> parameter specifies the numeric signal to be handled (see <citerefentry
  66     project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).</para>
  67
  68     <para>The <parameter>handler</parameter> parameter is a function to call when the signal is received or
  69     <constant>NULL</constant>. The handler function will be passed the <parameter>userdata</parameter>
  70     pointer, which may be chosen freely by the caller. The handler also receives a pointer to a
  71     <structname>signalfd_siginfo</structname> structure containing information about the received signal. See
  72     <citerefentry
  73     project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
  74     further information. The handler may return negative to signal an error (see below), other return values
  75     are ignored. If <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
  76     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
  77     used.</para>
  78
  79     <para>Only a single handler may be installed for a specific signal. The signal must be blocked in all
  80     threads before this function is called (using <citerefentry
  81     project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
  82     <citerefentry
  83     project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry>). For
  84     convenience, if the special flag <constant>SD_EVENT_SIGNAL_PROCMASK</constant> is ORed into the specified
  85     signal the signal will be automatically masked as necessary, for the calling thread. Note that this only
  86     works reliably if the signal is already masked in all other threads of the process, or if there are no
  87     other threads at the moment of invocation.</para>
  88
  89     <para>By default, the event source is enabled permanently (<constant>SD_EVENT_ON</constant>), but this
  90     may be changed with
  91     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  92     If the handler function returns a negative error code, it will either be disabled after the invocation,
  93     even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to
  94     terminate, see
  95     <citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  96     </para>
  97
  98     <para>To destroy an event source object use
  99     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 100     but note that the event source is only removed from the event loop
 101     when all references to the event source are dropped. To make sure
 102     an event source does not fire anymore, even if it is still referenced,
 103     disable the event source using
 104     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 105     with <constant>SD_EVENT_OFF</constant>.</para>
 106
 107     <para>If the second parameter of
 108     <function>sd_event_add_signal()</function> is
 109     <constant>NULL</constant> no reference to the event source object
 110     is returned. In this case the event source is considered
 111     "floating", and will be destroyed implicitly when the event loop
 112     itself is destroyed.</para>
 113
 114     <para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_signal()</function> is
 115     <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
 116     event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
 117     the exit code parameter to
 118     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 119
 120     <para><function>sd_event_source_get_signal()</function> returns
 121     the configured signal number of an event source created previously
 122     with <function>sd_event_add_signal()</function>. It takes the
 123     event source object as the <parameter>source</parameter>
 124     parameter.</para>
 125   </refsect1>
 126
 127   <refsect1>
 128     <title>Return Value</title>
 129
 130     <para>On success, these functions return 0 or a positive
 131     integer. On failure, they return a negative errno-style error
 132     code.</para>
 133
 134     <refsect2>
 135       <title>Errors</title>
 136
 137       <para>Returned errors may indicate the following problems:</para>
 138
 139       <variablelist>
 140         <varlistentry>
 141           <term><constant>-ENOMEM</constant></term>
 142
 143           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 144         </varlistentry>
 145
 146         <varlistentry>
 147           <term><constant>-EINVAL</constant></term>
 148
 149           <listitem><para>An invalid argument has been passed.</para></listitem>
 150         </varlistentry>
 151
 152         <varlistentry>
 153           <term><constant>-EBUSY</constant></term>
 154
 155           <listitem><para>A handler is already installed for this
 156           signal or the signal was not blocked previously.</para></listitem>
 157         </varlistentry>
 158
 159         <varlistentry>
 160           <term><constant>-ESTALE</constant></term>
 161
 162           <listitem><para>The event loop is already terminated.</para></listitem>
 163         </varlistentry>
 164
 165         <varlistentry>
 166           <term><constant>-ECHILD</constant></term>
 167
 168           <listitem><para>The event loop has been created in a different process, library or module instance.</para></listitem>
 169         </varlistentry>
 170
 171         <varlistentry>
 172           <term><constant>-EDOM</constant></term>
 173
 174           <listitem><para>The passed event source is not a signal event source.</para></listitem>
 175         </varlistentry>
 176
 177       </variablelist>
 178     </refsect2>
 179   </refsect1>
 180
 181   <xi:include href="libsystemd-pkgconfig.xml" />
 182
 183   <refsect1>
 184     <title>History</title>
 185     <para><function>sd_event_add_signal()</function>,
 186     <function>sd_event_signal_handler_t()</function>, and
 187     <function>sd_event_source_get_signal()</function> were added in version 217.</para>
 188   </refsect1>
 189
 190   <refsect1>
 191     <title>See Also</title>
 192
 193     <para><simplelist type="inline">
 194       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 195       <member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 196       <member><citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 197       <member><citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 198       <member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 199       <member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 200       <member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 201       <member><citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 202       <member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 203       <member><citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 204       <member><citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 205       <member><citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 206       <member><citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 207       <member><citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
 208       <member><citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 209       <member><citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 210       <member><citerefentry project='man-pages'><refentrytitle>pthread_sigmask</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 211     </simplelist></para>
 212   </refsect1>
 213
 214 </refentry>