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   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright 2015 Lennart Poettering
   9 -->
  10
  11 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
  12
  13   <refentryinfo>
  14     <title>sd_event_source_set_prepare</title>
  15     <productname>elogind</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Lennart</firstname>
  21         <surname>Poettering</surname>
  22         <email>lennart@poettering.net</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>sd_event_source_set_prepare</refentrytitle>
  29     <manvolnum>3</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>sd_event_source_set_prepare</refname>
  34
  35     <refpurpose>Set a preparation callback for event sources</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_source_set_prepare</function></funcdef>
  44         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  45         <paramdef>sd_event_handler_t <parameter>callback</parameter></paramdef>
  46       </funcprototype>
  47
  48       <funcprototype>
  49         <funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
  50         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  51         <paramdef>void *<parameter>userdata</parameter></paramdef>
  52       </funcprototype>
  53
  54     </funcsynopsis>
  55   </refsynopsisdiv>
  56
  57   <refsect1>
  58     <title>Description</title>
  59
  60     <para><function>sd_event_source_set_prepare()</function> may be
  61     used to set a preparation callback for the event source object
  62     specified as <parameter>source</parameter>. The callback function
  63     specified as <parameter>callback</parameter> will be invoked
  64     immediately before the event loop goes to sleep to wait for
  65     incoming events. It is invoked with the user data pointer passed
  66     when the event source was created. The event source will be disabled
  67     if the callback function returns a negative error code. The callback
  68     function may be used to reconfigure the precise events to wait for.
  69     If the <parameter>callback</parameter> parameter is passed as NULL
  70     the callback function is reset. </para>
  71
  72     <para>Event source objects have no preparation callback associated
  73     when they are first created with calls such as
  74     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  75     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  76     callback functions are supported for all event source types with
  77     the exception of those created with
  78     <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  79     callback functions are dispatched in the order indicated by the
  80     event source's priority field, as set with
  81     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  82     callbacks of disabled event sources (see
  83     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  84     are not invoked.</para>
  85   </refsect1>
  86
  87   <refsect1>
  88     <title>Return Value</title>
  89
  90     <para>On success,
  91     <function>sd_event_source_set_prepare()</function> returns a
  92     non-negative integer. On failure, it returns a negative
  93     errno-style error code.</para>
  94   </refsect1>
  95
  96   <refsect1>
  97     <title>Errors</title>
  98
  99     <para>Returned errors may indicate the following problems:</para>
 100
 101     <variablelist>
 102       <varlistentry>
 103         <term><constant>-EINVAL</constant></term>
 104
 105         <listitem><para><parameter>source</parameter> is not a valid
 106         pointer to an <structname>sd_event_source</structname>
 107         object.</para></listitem>
 108       </varlistentry>
 109
 110       <varlistentry>
 111         <term><constant>-ESTALE</constant></term>
 112
 113         <listitem><para>The event loop is already terminated.</para></listitem>
 114
 115       </varlistentry>
 116       <varlistentry>
 117         <term><constant>-ENOMEM</constant></term>
 118
 119         <listitem><para>Not enough memory.</para></listitem>
 120       </varlistentry>
 121
 122       <varlistentry>
 123         <term><constant>-ECHILD</constant></term>
 124
 125         <listitem><para>The event loop has been created in a different process.</para></listitem>
 126
 127       </varlistentry>
 128
 129       <varlistentry>
 130         <term><constant>-EDOM</constant></term>
 131
 132         <listitem><para>The specified event source has been created
 133         with
 134         <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 135
 136       </varlistentry>
 137
 138     </variablelist>
 139   </refsect1>
 140
 141   <xi:include href="libelogind-pkgconfig.xml" />
 142
 143   <refsect1>
 144     <title>See Also</title>
 145
 146     <para>
 147       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 148       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 149       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 150       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 151       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 152       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 155       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 156     </para>
 157   </refsect1>
 158
 159 </refentry>