man/sd_event_source_set_prepare.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//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,
  77     <function>sd_event_source_set_prepare()</function> returns a
  78     non-negative integer. 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>source</parameter> is not a valid
  92         pointer to an <structname>sd_event_source</structname>
  93         object.</para></listitem>
  94       </varlistentry>
  95
  96       <varlistentry>
  97         <term><constant>-ESTALE</constant></term>
  98
  99         <listitem><para>The event loop is already terminated.</para></listitem>
 100
 101       </varlistentry>
 102       <varlistentry>
 103         <term><constant>-ENOMEM</constant></term>
 104
 105         <listitem><para>Not enough memory.</para></listitem>
 106       </varlistentry>
 107
 108       <varlistentry>
 109         <term><constant>-ECHILD</constant></term>
 110
 111         <listitem><para>The event loop has been created in a different process.</para></listitem>
 112
 113       </varlistentry>
 114
 115       <varlistentry>
 116         <term><constant>-EDOM</constant></term>
 117
 118         <listitem><para>The specified event source has been created
 119         with
 120         <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 121
 122       </varlistentry>
 123
 124     </variablelist>
 125   </refsect1>
 126
 127   <xi:include href="libsystemd-pkgconfig.xml" />
 128
 129   <refsect1>
 130     <title>See Also</title>
 131
 132     <para>
 133       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 134       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 135       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 136       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 139       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 140       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 141       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 142       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 143     </para>
 144   </refsect1>
 145
 146 </refentry>