man/sd_event_source_set_prepare.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 2015 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>sd_event_source_set_prepare</title>
  17     <productname>elogind</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_event_source_set_prepare</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_event_source_set_prepare</refname>
  36
  37     <refpurpose>Set a preparation callback for event sources</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_source_set_prepare</function></funcdef>
  46         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  47         <paramdef>sd_event_handler_t <parameter>callback</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
  52         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  53         <paramdef>void *<parameter>userdata</parameter></paramdef>
  54       </funcprototype>
  55
  56     </funcsynopsis>
  57   </refsynopsisdiv>
  58
  59   <refsect1>
  60     <title>Description</title>
  61
  62     <para><function>sd_event_source_set_prepare()</function> may be
  63     used to set a preparation callback for the event source object
  64     specified as <parameter>source</parameter>. The callback function
  65     specified as <parameter>callback</parameter> will be invoked
  66     immediately before the event loop goes to sleep to wait for
  67     incoming events. It is invoked with the user data pointer passed
  68     when the event source was created. The event source will be disabled
  69     if the callback function returns a negative error code. The callback
  70     function may be used to reconfigure the precise events to wait for.
  71     If the <parameter>callback</parameter> parameter is passed as NULL
  72     the callback function is reset. </para>
  73
  74     <para>Event source objects have no preparation callback associated
  75     when they are first created with calls such as
  76     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  77     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  78     callback functions are supported for all event source types with
  79     the exception of those created with
  80     <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  81     callback functions are dispatched in the order indicated by the
  82     event source's priority field, as set with
  83     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  84     callbacks of disabled event sources (see
  85     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  86     are not invoked.</para>
  87   </refsect1>
  88
  89   <refsect1>
  90     <title>Return Value</title>
  91
  92     <para>On success,
  93     <function>sd_event_source_set_prepare()</function> returns a
  94     non-negative integer. On failure, it returns a negative
  95     errno-style error code.</para>
  96   </refsect1>
  97
  98   <refsect1>
  99     <title>Errors</title>
 100
 101     <para>Returned errors may indicate the following problems:</para>
 102
 103     <variablelist>
 104       <varlistentry>
 105         <term><constant>-EINVAL</constant></term>
 106
 107         <listitem><para><parameter>source</parameter> is not a valid
 108         pointer to an <structname>sd_event_source</structname>
 109         object.</para></listitem>
 110       </varlistentry>
 111
 112       <varlistentry>
 113         <term><constant>-ESTALE</constant></term>
 114
 115         <listitem><para>The event loop is already terminated.</para></listitem>
 116
 117       </varlistentry>
 118       <varlistentry>
 119         <term><constant>-ENOMEM</constant></term>
 120
 121         <listitem><para>Not enough memory.</para></listitem>
 122       </varlistentry>
 123
 124       <varlistentry>
 125         <term><constant>-ECHILD</constant></term>
 126
 127         <listitem><para>The event loop has been created in a different process.</para></listitem>
 128
 129       </varlistentry>
 130
 131       <varlistentry>
 132         <term><constant>-EDOM</constant></term>
 133
 134         <listitem><para>The specified event source has been created
 135         with
 136         <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 137
 138       </varlistentry>
 139
 140     </variablelist>
 141   </refsect1>
 142
 143   <xi:include href="libelogind-pkgconfig.xml" />
 144
 145   <refsect1>
 146     <title>See Also</title>
 147
 148     <para>
 149       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 150       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 151       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 152       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 156       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 157       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 158     </para>
 159   </refsect1>
 160
 161 </refentry>