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">
6 SPDX-License-Identifier: LGPL-2.1+
8 Copyright 2015 Lennart Poettering
11 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
14 <title>sd_event_source_set_prepare</title>
15 <productname>elogind</productname>
19 <contrib>Developer</contrib>
20 <firstname>Lennart</firstname>
21 <surname>Poettering</surname>
22 <email>lennart@poettering.net</email>
28 <refentrytitle>sd_event_source_set_prepare</refentrytitle>
29 <manvolnum>3</manvolnum>
33 <refname>sd_event_source_set_prepare</refname>
35 <refpurpose>Set a preparation callback for event sources</refpurpose>
40 <funcsynopsisinfo>#include <elogind/sd-event.h></funcsynopsisinfo>
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>
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>
58 <title>Description</title>
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>
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>
88 <title>Return Value</title>
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>
99 <para>Returned errors may indicate the following problems:</para>
103 <term><constant>-EINVAL</constant></term>
105 <listitem><para><parameter>source</parameter> is not a valid
106 pointer to an <structname>sd_event_source</structname>
107 object.</para></listitem>
111 <term><constant>-ESTALE</constant></term>
113 <listitem><para>The event loop is already terminated.</para></listitem>
117 <term><constant>-ENOMEM</constant></term>
119 <listitem><para>Not enough memory.</para></listitem>
123 <term><constant>-ECHILD</constant></term>
125 <listitem><para>The event loop has been created in a different process.</para></listitem>
130 <term><constant>-EDOM</constant></term>
132 <listitem><para>The specified event source has been created
134 <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
141 <xi:include href="libelogind-pkgconfig.xml" />
144 <title>See Also</title>
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>