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   This file is part of elogind.
   7   SPDX-License-Identifier: LGPL-2.1+
   8
   9
  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
  11 -->
  12
  13 <refentry id="sd_event_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>sd_event_get_fd</title>
  17     <productname>elogind</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>More text</contrib>
  22         <firstname>Zbigniew</firstname>
  23         <surname>Jędrzejewski-Szmek</surname>
  24         <email>zbyszek@in.waw.pl</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_event_get_fd</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_event_get_fd</refname>
  36
  37     <refpurpose>Obtain a file descriptor to poll for event loop events</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;elogind/sd-event.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int <function>sd_event_get_fd</function></funcdef>
  46         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  47       </funcprototype>
  48
  49     </funcsynopsis>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54
  55     <para><function>sd_event_get_fd()</function> returns the file
  56     descriptor that an event loop object returned by the
  57     <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  58     function uses to wait for events. This file descriptor may itself
  59     be polled for
  60     <constant>POLLIN</constant>/<constant>EPOLLIN</constant>
  61     events. This makes it possible to embed an
  62     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  63     event loop into another, possibly foreign, event loop.</para>
  64
  65     <para>The returned file descriptor refers to an <citerefentry
  66     project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  67     object. It is recommended not to alter it by invoking
  68     <citerefentry
  69     project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
  70     on it, in order to avoid interference with the event loop's inner
  71     logic and assumptions.</para>
  72   </refsect1>
  73
  74   <refsect1>
  75     <title>Return Value</title>
  76
  77     <para>On success, <function>sd_event_get_fd()</function> returns a
  78     non-negative file descriptor. On failure, it returns a negative
  79     errno-style error code.</para>
  80   </refsect1>
  81
  82   <refsect1>
  83     <title>Errors</title>
  84
  85     <para>Returned errors may indicate the following problems:</para>
  86
  87     <variablelist>
  88       <varlistentry>
  89         <term><constant>-EINVAL</constant></term>
  90
  91         <listitem><para><parameter>event</parameter> is not a valid
  92         pointer to an <structname>sd_event</structname> structure.
  93         </para></listitem>
  94       </varlistentry>
  95
  96       <varlistentry>
  97         <term><constant>-ECHILD</constant></term>
  98
  99         <listitem><para>The event loop has been created in a different process.</para></listitem>
 100
 101       </varlistentry>
 102     </variablelist>
 103   </refsect1>
 104
 105   <refsect1>
 106     <title>Examples</title>
 107
 108     <example>
 109       <title>Integration in the GLib event loop</title>
 110
 111       <programlisting><xi:include href="glib-event-glue.c" parse="text" /></programlisting>
 112     </example>
 113   </refsect1>
 114
 115   <xi:include href="libelogind-pkgconfig.xml" />
 116
 117   <refsect1>
 118     <title>See Also</title>
 119
 120     <para>
 121       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 122       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 123       <citerefentry><refentrytitle>sd_event_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 124       <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 125       <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 126     </para>
 127   </refsect1>
 128
 129 </refentry>