man/sd_event_source_set_prepare.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_event_source_set_prepare</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_event_source_set_prepare</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_event_source_set_prepare</refname>
  20
  21     <refpurpose>Set a preparation callback for event sources</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <funcsynopsis>
  26       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  27
  28       <funcprototype>
  29         <funcdef>int <function>sd_event_source_set_prepare</function></funcdef>
  30         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  31         <paramdef>sd_event_handler_t <parameter>callback</parameter></paramdef>
  32       </funcprototype>
  33
  34       <funcprototype>
  35         <funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
  36         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  37         <paramdef>void *<parameter>userdata</parameter></paramdef>
  38       </funcprototype>
  39
  40     </funcsynopsis>
  41   </refsynopsisdiv>
  42
  43   <refsect1>
  44     <title>Description</title>
  45
  46     <para><function>sd_event_source_set_prepare()</function> may be
  47     used to set a preparation callback for the event source object
  48     specified as <parameter>source</parameter>. The callback function
  49     specified as <parameter>callback</parameter> will be invoked
  50     immediately before the event loop goes to sleep to wait for
  51     incoming events. It is invoked with the user data pointer passed
  52     when the event source was created. The event source will be disabled
  53     if the callback function returns a negative error code. The callback
  54     function may be used to reconfigure the precise events to wait for.
  55     If the <parameter>callback</parameter> parameter is passed as NULL
  56     the callback function is reset. </para>
  57
  58     <para>Event source objects have no preparation callback associated
  59     when they are first created with calls such as
  60     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  61     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  62     callback functions are supported for all event source types with
  63     the exception of those created with
  64     <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  65     callback functions are dispatched in the order indicated by the
  66     event source's priority field, as set with
  67     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  68     callbacks of disabled event sources (see
  69     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  70     are not invoked.</para>
  71   </refsect1>
  72
  73   <refsect1>
  74     <title>Return Value</title>
  75
  76     <para>On success, <function>sd_event_source_set_prepare()</function> returns a non-negative integer. On
  77     failure, it returns a negative errno-style error code.</para>
  78
  79     <refsect2>
  80       <title>Errors</title>
  81
  82       <para>Returned errors may indicate the following problems:</para>
  83
  84       <variablelist>
  85         <varlistentry>
  86           <term><constant>-EINVAL</constant></term>
  87
  88           <listitem><para><parameter>source</parameter> is not a valid pointer to an
  89           <structname>sd_event_source</structname> object.</para></listitem>
  90         </varlistentry>
  91
  92         <varlistentry>
  93           <term><constant>-ESTALE</constant></term>
  94
  95           <listitem><para>The event loop is already terminated.</para></listitem>
  96
  97         </varlistentry>
  98         <varlistentry>
  99           <term><constant>-ENOMEM</constant></term>
 100
 101           <listitem><para>Not enough memory.</para></listitem>
 102         </varlistentry>
 103
 104         <varlistentry>
 105           <term><constant>-ECHILD</constant></term>
 106
 107           <listitem><para>The event loop has been created in a different process.</para></listitem>
 108
 109         </varlistentry>
 110
 111         <varlistentry>
 112           <term><constant>-EDOM</constant></term>
 113
 114           <listitem><para>The specified event source has been created with
 115           <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 116
 117         </varlistentry>
 118
 119       </variablelist>
 120     </refsect2>
 121   </refsect1>
 122
 123   <xi:include href="libsystemd-pkgconfig.xml" />
 124
 125   <refsect1>
 126     <title>See Also</title>
 127
 128     <para>
 129       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 130       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 131       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 132       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 133       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 134       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 135       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 136       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 139     </para>
 140   </refsect1>
 141
 142 </refentry>