man/sd_event_get_fd.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright © 2014 Zbigniew Jędrzejewski-Szmek
   9 -->
  10
  11 <refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>sd_event_get_fd</title>
  15     <productname>elogind</productname>
  16   </refentryinfo>
  17
  18   <refmeta>
  19     <refentrytitle>sd_event_get_fd</refentrytitle>
  20     <manvolnum>3</manvolnum>
  21   </refmeta>
  22
  23   <refnamediv>
  24     <refname>sd_event_get_fd</refname>
  25
  26     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  27   </refnamediv>
  28
  29   <refsynopsisdiv>
  30     <funcsynopsis>
  31       <funcsynopsisinfo>#include &lt;elogind/sd-event.h&gt;</funcsynopsisinfo>
  32
  33       <funcprototype>
  34         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  35         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  36       </funcprototype>
  37
  38     </funcsynopsis>
  39   </refsynopsisdiv>
  40
  41   <refsect1>
  42     <title>Description</title>
  43
  44     <para><function>sd_event_get_fd()</function> returns the file
  45     descriptor that an event loop object returned by the
  46     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  47     function uses to wait for events. This file descriptor may itself
  48     be polled for
  49     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  50     events. This makes it possible to embed an
  51     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  52     event loop into another, possibly foreign, event loop.</para>
  53
  54     <para>The returned file descriptor refers to an <citerefentry
  55     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  56     object. It is recommended not to alter it by invoking
  57     <citerefentry
  58     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  59     on it, in order to avoid interference with the event loop's inner
  60     logic and assumptions.</para>
  61   </refsect1>
  62
  63   <refsect1>
  64     <title>Return Value</title>
  65
  66     <para>On success, <function>sd_event_get_fd()</function> returns a
  67     non-negative file descriptor. On failure, it returns a negative
  68     errno-style error code.</para>
  69   </refsect1>
  70
  71   <refsect1>
  72     <title>Errors</title>
  73
  74     <para>Returned errors may indicate the following problems:</para>
  75
  76     <variablelist>
  77       <varlistentry>
  78         <term><constant>-EINVAL</constant></term>
  79
  80         <listitem><para><parameter>event</parameter> is not a valid
  81         pointer to an <structname>sd_event</structname> structure.
  82         </para></listitem>
  83       </varlistentry>
  84
  85       <varlistentry>
  86         <term><constant>-ECHILD</constant></term>
  87
  88         <listitem><para>The event loop has been created in a different process.</para></listitem>
  89
  90       </varlistentry>
  91     </variablelist>
  92   </refsect1>
  93
  94   <refsect1>
  95     <title>Examples</title>
  96
  97     <example>
  98       <title>Integration in the GLib event loop</title>
  99
 100       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
 101     </example>
 102   </refsect1>
 103
 104   <xi:include href="libelogind-pkgconfig.xml" />
 105
 106   <refsect1>
 107     <title>See Also</title>
 108
 109     <para>
 110       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 111       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 112       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 113       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 114       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 115     </para>
 116   </refsect1>
 117
 118 </refentry>