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