man/sd_event_wait.xml

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  23
  24 <refentry id="sd_event_wait">
  25
  26   <refentryinfo>
  27     <title>sd_event_wait</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Tom</firstname>
  34         <surname>Gundersen</surname>
  35         <email>teg@jklm.no</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_wait</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_wait</refname>
  47     <refname>sd_event_prepare</refname>
  48     <refname>sd_event_dispatch</refname>
  49
  50     <refpurpose>Run parts of the libsystemd event loop</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <funcsynopsis>
  55       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  56
  57       <funcprototype>
  58         <funcdef>int <function>sd_event_prepare</function></funcdef>
  59         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  60       </funcprototype>
  61
  62       <funcprototype>
  63         <funcdef>int <function>sd_event_wait</function></funcdef>
  64         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  65         <paramdef>uint64_t <parameter>timeout</parameter></paramdef>
  66       </funcprototype>
  67
  68       <funcprototype>
  69         <funcdef>int <function>sd_event_dispatch</function></funcdef>
  70         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  71       </funcprototype>
  72
  73     </funcsynopsis>
  74   </refsynopsisdiv>
  75
  76   <refsect1>
  77     <title>Description</title>
  78
  79     <para>Functions described here form parts of an event loop.</para>
  80
  81     <para><function>sd_event_prepare</function> checks for pending
  82     events and arms necessary timers. If any events are ready to be
  83     processed, it returns a positive value, and the events should be
  84     processed with <function>sd_event_dispatch</function>.
  85     <function>sd_event_dispatch</function> runs a handler for one of
  86     the events from the sources with the highest priority. On success,
  87     <function>sd_event_dispatch</function> returns either 0, which
  88     means that the loop is finished, or a positive value, which means
  89     that the loop is again in the initial state and
  90     <function>sd_event_prepare</function> should be called again.
  91     </para>
  92
  93     <para>In case <function>sd_event_prepare</function> returned 0,
  94     <function>sd_event_wait</function> should be called to wait for
  95     events or a timeout. If any events are ready to be processed, it
  96     returns a positive value, and the events should be processed with
  97     <function>sd_event_dispatch</function>. Otherwise, the loop is
  98     back in the initial state and <function>sd_event_prepare</function>
  99     should be called again.</para>
 100
 101     <programlisting>
 102              ┌──────────┐
 103              │ initial  ├──←←←←←←←←←←←←←←←←←←←─┐
 104              └───┬──────┘                      ↑
 105                  │                             ↑
 106            sd_event_prepare   ┌─────────┐      ↑
 107                  ├ 0 →→→→→→→──┤  armed  │      ↑
 108                  1            └───┬─────┘      ↑
 109                  ↓                │            ↑
 110                  ↓           sd_event_wait     ↑
 111                  ├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘
 112              ┌───┴──────┐                      ↑
 113              │ pending  │                      ↑
 114              └───┬──────┘                      ↑
 115                  │                             ↑
 116            sd_event_dispatch                   ↑
 117                  ↓                             ↑
 118                  ├ 1 ──────────→→→→→→→─────────┘
 119                  0
 120                  ↓
 121              ┌───┴──────┐
 122              │ finished │
 123              └──────────┘
 124     </programlisting>
 125
 126     <para>All three functions take, as the first argument, the event
 127     loop object <parameter>event</parameter> that is created with
 128     <function>sd_event_new</function>. The timeout for
 129     <function>sd_event_wait</function> is specified with
 130     <parameter>timeout</parameter> in milliseconds.
 131     <constant>(uint64_t) -1</constant> may be used to specify an
 132     infinite timeout.</para>
 133   </refsect1>
 134
 135   <refsect1>
 136     <title>Return Value</title>
 137
 138     <para>On success, these functions return 0 or a positive integer.
 139     On failure, they return a negative errno-style error code. In case
 140     of <function>sd_event_prepare</function> and
 141     <function>sd_event_wait</function>, a positive value means that
 142     events are ready to be processed and 0 means that no events are
 143     ready. In case of <function>sd_event_dispatch</function>, a
 144     positive value means that the loop is again in the initial state
 145     and 0 means the loop is finished. For any of these functions, a
 146     negative return value means the loop must be aborted.</para>
 147   </refsect1>
 148
 149   <refsect1>
 150     <title>Errors</title>
 151
 152     <para>Returned errors may indicate the following problems:</para>
 153
 154     <variablelist>
 155       <varlistentry>
 156         <term><constant>-EINVAL</constant></term>
 157
 158         <listitem><para>The <parameter>event</parameter> parameter is
 159         <constant>NULL</constant>.</para></listitem>
 160       </varlistentry>
 161
 162       <varlistentry>
 163         <term><constant>-EBUSY</constant></term>
 164
 165         <listitem><para>The event loop object is not in the right
 166         state.</para></listitem>
 167       </varlistentry>
 168
 169       <varlistentry>
 170         <term><constant>-ESTALE</constant></term>
 171
 172         <listitem><para>The event loop is already terminated.</para></listitem>
 173
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term><constant>-ECHILD</constant></term>
 178
 179         <listitem><para>The event loop has been created in a different process.</para></listitem>
 180
 181       </varlistentry>
 182
 183     </variablelist>
 184
 185     <para>Other errors are possible, too.</para>
 186   </refsect1>
 187
 188   <refsect1>
 189     <title>Notes</title>
 190
 191     <para>Functions described here are available
 192     as a shared library, which can be compiled and linked to with the
 193     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 194     file.</para>
 195   </refsect1>
 196
 197   <refsect1>
 198     <title>See Also</title>
 199
 200     <para>
 201       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 202       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 203       <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 204       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 205       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 206       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 207       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 208       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 209       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 210     </para>
 211   </refsect1>
 212
 213 </refentry>