man/sd_event_add_signal.xml

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   8   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  23
  24 <refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_add_signal</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>More text</contrib>
  33         <firstname>Zbigniew</firstname>
  34         <surname>Jędrzejewski-Szmek</surname>
  35         <email>zbyszek@in.waw.pl</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_add_signal</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_add_signal</refname>
  47     <refname>sd_event_source_get_signal</refname>
  48     <refname>sd_event_signal_handler_t</refname>
  49
  50     <refpurpose>Add a UNIX process signal event source to an event
  51     loop</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <funcsynopsis>
  56       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  57
  58       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  59
  60       <funcprototype>
  61         <funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
  62         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  63         <paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
  64         <paramdef>void *<parameter>userdata</parameter></paramdef>
  65       </funcprototype>
  66
  67       <funcprototype>
  68         <funcdef>int <function>sd_event_add_signal</function></funcdef>
  69         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  70         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  71         <paramdef>int <parameter>signal</parameter></paramdef>
  72         <paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
  73         <paramdef>void *<parameter>userdata</parameter></paramdef>
  74       </funcprototype>
  75
  76       <funcprototype>
  77         <funcdef>int <function>sd_event_source_get_signal</function></funcdef>
  78         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  79       </funcprototype>
  80
  81     </funcsynopsis>
  82   </refsynopsisdiv>
  83
  84   <refsect1>
  85     <title>Description</title>
  86
  87     <para><function>sd_event_add_signal()</function> adds a new UNIX
  88     process signal event source to an event loop. The event loop
  89     object is specified in the <parameter>event</parameter> parameter,
  90     and the event source object is returned in the
  91     <parameter>source</parameter> parameter. The
  92     <parameter>signal</parameter> parameter specifies the numeric
  93     signal to be handled (see <citerefentry
  94     project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
  95     The <parameter>handler</parameter> parameter must reference a
  96     function to call when the signal is received or be
  97     <constant>NULL</constant>.  The handler function will be passed
  98     the <parameter>userdata</parameter> pointer, which may be chosen
  99     freely by the caller. The handler also receives a pointer to a
 100     <structname>signalfd_siginfo</structname> structure containing
 101     information about the received signal. See <citerefentry
 102     project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 103     for further information.</para>
 104
 105     <para>Only a single handler may be installed for a specific
 106     signal. The signal will be unblocked by this call, and must be
 107     blocked before this function is called in all threads (using
 108     <citerefentry
 109     project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
 110     the handler is not specified (<parameter>handler</parameter> is
 111     <constant>NULL</constant>), a default handler which causes the
 112     program to exit cleanly will be used.</para>
 113
 114     <para>By default, the event source is enabled permanently
 115     (<constant>SD_EVENT_ON</constant>), but this may be changed with
 116     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 117     If the handler function returns a negative error code, it will be
 118     disabled after the invocation, even if the
 119     <constant>SD_EVENT_ON</constant> mode was requested before.
 120     </para>
 121
 122     <para>To destroy an event source object use
 123     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 124     but note that the event source is only removed from the event loop
 125     when all references to the event source are dropped. To make sure
 126     an event source does not fire anymore, even if it is still referenced,
 127     disable the event source using
 128     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 129     with <constant>SD_EVENT_OFF</constant>.</para>
 130
 131     <para>If the second parameter of
 132     <function>sd_event_add_signal()</function> is
 133     <constant>NULL</constant> no reference to the event source object
 134     is returned. In this case the event source is considered
 135     "floating", and will be destroyed implicitly when the event loop
 136     itself is destroyed.</para>
 137
 138     <para><function>sd_event_source_get_signal()</function> returns
 139     the configured signal number of an event source created previously
 140     with <function>sd_event_add_signal()</function>. It takes the
 141     event source object as the <parameter>source</parameter>
 142     parameter.</para>
 143   </refsect1>
 144
 145   <refsect1>
 146     <title>Return Value</title>
 147
 148     <para>On success, these functions return 0 or a positive
 149     integer. On failure, they return a negative errno-style error
 150     code.</para>
 151   </refsect1>
 152
 153   <refsect1>
 154     <title>Errors</title>
 155
 156     <para>Returned errors may indicate the following problems:</para>
 157
 158     <variablelist>
 159       <varlistentry>
 160         <term><constant>-ENOMEM</constant></term>
 161
 162         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 163       </varlistentry>
 164
 165       <varlistentry>
 166         <term><constant>-EINVAL</constant></term>
 167
 168         <listitem><para>An invalid argument has been passed.</para></listitem>
 169       </varlistentry>
 170
 171       <varlistentry>
 172         <term><constant>-EBUSY</constant></term>
 173
 174         <listitem><para>A handler is already installed for this
 175         signal or the signal was not blocked previously.</para></listitem>
 176       </varlistentry>
 177
 178       <varlistentry>
 179         <term><constant>-ESTALE</constant></term>
 180
 181         <listitem><para>The event loop is already terminated.</para></listitem>
 182       </varlistentry>
 183
 184       <varlistentry>
 185         <term><constant>-ECHILD</constant></term>
 186
 187         <listitem><para>The event loop has been created in a different process.</para></listitem>
 188       </varlistentry>
 189
 190       <varlistentry>
 191         <term><constant>-EDOM</constant></term>
 192
 193         <listitem><para>The passed event source is not a signal event source.</para></listitem>
 194       </varlistentry>
 195
 196     </variablelist>
 197   </refsect1>
 198
 199   <xi:include href="libsystemd-pkgconfig.xml" />
 200
 201   <refsect1>
 202     <title>See Also</title>
 203
 204     <para>
 205       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 206       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 207       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 208       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 209       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 210       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 211       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 212       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 213       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 214       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 215       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 216       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 217       <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 218     </para>
 219   </refsect1>
 220
 221 </refentry>