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 when there's still a
 127     reference to it kept, consider setting the event source to
 128     <constant>SD_EVENT_OFF</constant> with
 129     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 130
 131     <para>If the the second parameter of
 132     <function>sd_event_add_signal()</function> is passed as NULL no
 133     reference to the event source object is returned. In this case the
 134     event source is considered "floating", and will be destroyed
 135     implicitly when the event loop itself is destroyed.</para>
 136
 137     <para><function>sd_event_source_get_signal()</function> retrieves
 138     the configured UNIX process signal number of a signal event source
 139     created previously with
 140     <function>sd_event_add_signal()</function>. It takes the event
 141     source object as the <parameter>source</parameter>
 142     parameter.</para>
 143
 144   </refsect1>
 145
 146   <refsect1>
 147     <title>Return Value</title>
 148
 149     <para>On success, these functions return 0 or a positive
 150     integer. On failure, they return a negative errno-style error
 151     code. </para>
 152   </refsect1>
 153
 154   <refsect1>
 155     <title>Errors</title>
 156
 157     <para>Returned errors may indicate the following problems:</para>
 158
 159     <variablelist>
 160       <varlistentry>
 161         <term><constant>-ENOMEM</constant></term>
 162
 163         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 164       </varlistentry>
 165
 166       <varlistentry>
 167         <term><constant>-EINVAL</constant></term>
 168
 169         <listitem><para>An invalid argument has been passed.</para></listitem>
 170
 171       </varlistentry>
 172
 173       <varlistentry>
 174         <term><constant>-EBUSY</constant></term>
 175
 176         <listitem><para>A handler is already installed for this
 177         signal or the signal was not blocked previously.</para></listitem>
 178
 179       </varlistentry>
 180
 181       <varlistentry>
 182         <term><constant>-ESTALE</constant></term>
 183
 184         <listitem><para>The event loop is already terminated.</para></listitem>
 185
 186       </varlistentry>
 187
 188       <varlistentry>
 189         <term><constant>-ECHILD</constant></term>
 190
 191         <listitem><para>The event loop has been created in a different process.</para></listitem>
 192
 193       </varlistentry>
 194
 195       <varlistentry>
 196         <term><constant>-EDOM</constant></term>
 197
 198         <listitem><para>The passed event source is not a signal event source.</para></listitem>
 199       </varlistentry>
 200
 201     </variablelist>
 202   </refsect1>
 203
 204   <xi:include href="libsystemd-pkgconfig.xml" />
 205
 206   <refsect1>
 207     <title>See Also</title>
 208
 209     <para>
 210       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 211       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 212       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 213       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 214       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 215       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 216       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 217       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 218       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 219       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 220       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 221       <citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 222       <citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 223     </para>
 224   </refsect1>
 225
 226 </refentry>