man/sd_event_source_set_prepare.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   6   SPDX-License-Identifier: LGPL-2.1+
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   8
   9 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
  10
  11   <refentryinfo>
  12     <title>sd_event_source_set_prepare</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>sd_event_source_set_prepare</refentrytitle>
  18     <manvolnum>3</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>sd_event_source_set_prepare</refname>
  23
  24     <refpurpose>Set a preparation callback for event sources</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <funcsynopsis>
  29       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  30
  31       <funcprototype>
  32         <funcdef>int <function>sd_event_source_set_prepare</function></funcdef>
  33         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  34         <paramdef>sd_event_handler_t <parameter>callback</parameter></paramdef>
  35       </funcprototype>
  36
  37       <funcprototype>
  38         <funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
  39         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  40         <paramdef>void *<parameter>userdata</parameter></paramdef>
  41       </funcprototype>
  42
  43     </funcsynopsis>
  44   </refsynopsisdiv>
  45
  46   <refsect1>
  47     <title>Description</title>
  48
  49     <para><function>sd_event_source_set_prepare()</function> may be
  50     used to set a preparation callback for the event source object
  51     specified as <parameter>source</parameter>. The callback function
  52     specified as <parameter>callback</parameter> will be invoked
  53     immediately before the event loop goes to sleep to wait for
  54     incoming events. It is invoked with the user data pointer passed
  55     when the event source was created. The event source will be disabled
  56     if the callback function returns a negative error code. The callback
  57     function may be used to reconfigure the precise events to wait for.
  58     If the <parameter>callback</parameter> parameter is passed as NULL
  59     the callback function is reset. </para>
  60
  61     <para>Event source objects have no preparation callback associated
  62     when they are first created with calls such as
  63     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  64     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  65     callback functions are supported for all event source types with
  66     the exception of those created with
  67     <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  68     callback functions are dispatched in the order indicated by the
  69     event source's priority field, as set with
  70     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  71     callbacks of disabled event sources (see
  72     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  73     are not invoked.</para>
  74   </refsect1>
  75
  76   <refsect1>
  77     <title>Return Value</title>
  78
  79     <para>On success,
  80     <function>sd_event_source_set_prepare()</function> returns a
  81     non-negative integer. On failure, it returns a negative
  82     errno-style error code.</para>
  83   </refsect1>
  84
  85   <refsect1>
  86     <title>Errors</title>
  87
  88     <para>Returned errors may indicate the following problems:</para>
  89
  90     <variablelist>
  91       <varlistentry>
  92         <term><constant>-EINVAL</constant></term>
  93
  94         <listitem><para><parameter>source</parameter> is not a valid
  95         pointer to an <structname>sd_event_source</structname>
  96         object.</para></listitem>
  97       </varlistentry>
  98
  99       <varlistentry>
 100         <term><constant>-ESTALE</constant></term>
 101
 102         <listitem><para>The event loop is already terminated.</para></listitem>
 103
 104       </varlistentry>
 105       <varlistentry>
 106         <term><constant>-ENOMEM</constant></term>
 107
 108         <listitem><para>Not enough memory.</para></listitem>
 109       </varlistentry>
 110
 111       <varlistentry>
 112         <term><constant>-ECHILD</constant></term>
 113
 114         <listitem><para>The event loop has been created in a different process.</para></listitem>
 115
 116       </varlistentry>
 117
 118       <varlistentry>
 119         <term><constant>-EDOM</constant></term>
 120
 121         <listitem><para>The specified event source has been created
 122         with
 123         <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 124
 125       </varlistentry>
 126
 127     </variablelist>
 128   </refsect1>
 129
 130   <xi:include href="libsystemd-pkgconfig.xml" />
 131
 132   <refsect1>
 133     <title>See Also</title>
 134
 135     <para>
 136       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 137       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 138       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 139       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 140       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 141       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 142       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 143       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 144       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 145     </para>
 146   </refsect1>
 147
 148 </refentry>