man/sd_event_source_set_prepare.xml

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  23
  24 <refentry id="sd_event_source_set_prepare" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_source_set_prepare</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_source_set_prepare</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_source_set_prepare</refname>
  47
  48     <refpurpose>Set a preparation callback for event sources</refpurpose>
  49   </refnamediv>
  50
  51   <refsynopsisdiv>
  52     <funcsynopsis>
  53       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  54
  55       <funcprototype>
  56         <funcdef>int <function>sd_event_source_set_prepare</function></funcdef>
  57         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  58         <paramdef>sd_event_handler_t <parameter>callback</parameter></paramdef>
  59       </funcprototype>
  60
  61       <funcprototype>
  62         <funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
  63         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  64         <paramdef>void *<parameter>userdata</parameter></paramdef>
  65       </funcprototype>
  66
  67     </funcsynopsis>
  68   </refsynopsisdiv>
  69
  70   <refsect1>
  71     <title>Description</title>
  72
  73     <para><function>sd_event_source_set_prepare()</function> may be
  74     used to set a preparation callback for the event source object
  75     specified as <parameter>source</parameter>. The callback function
  76     specified as <parameter>callback</parameter> will be invoked
  77     immediately before the event loop goes to sleep to wait for
  78     incoming events. It is invoked with the user data pointer passed
  79     when the event source was created. The callback function may be
  80     used to reconfigure the precise events to wait for. If the
  81     <parameter>callback</parameter> parameter is passed as NULL the
  82     callback function is reset. </para>
  83
  84     <para>Event source objects have no preparation callback associated
  85     when they are first created with calls such as
  86     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  87     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  88     callback functions are supported for all event source types with
  89     the exception of those created with
  90     <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  91     callback functions are dispatched in the order indicated by the
  92     event source's priority field, as set with
  93     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Preparation
  94     callbacks of disabled event sources (see
  95     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  96     are not invoked.</para>
  97   </refsect1>
  98
  99   <refsect1>
 100     <title>Return Value</title>
 101
 102     <para>On success,
 103     <function>sd_event_source_set_prepare()</function> returns a
 104     non-negative integer. On failure, it returns a negative
 105     errno-style error code.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>Errors</title>
 110
 111     <para>Returned errors may indicate the following problems:</para>
 112
 113     <variablelist>
 114       <varlistentry>
 115         <term><constant>-EINVAL</constant></term>
 116
 117         <listitem><para><parameter>source</parameter> is not a valid
 118         pointer to an <structname>sd_event_source</structname>
 119         object.</para></listitem>
 120       </varlistentry>
 121
 122       <varlistentry>
 123         <term><constant>-ESTALE</constant></term>
 124
 125         <listitem><para>The event loop is already terminated.</para></listitem>
 126
 127       </varlistentry>
 128       <varlistentry>
 129         <term><constant>-ENOMEM</constant></term>
 130
 131         <listitem><para>Not enough memory.</para></listitem>
 132       </varlistentry>
 133
 134       <varlistentry>
 135         <term><constant>-ECHILD</constant></term>
 136
 137         <listitem><para>The event loop has been created in a different process.</para></listitem>
 138
 139       </varlistentry>
 140
 141       <varlistentry>
 142         <term><constant>-EDOM</constant></term>
 143
 144         <listitem><para>The specified event source has been created
 145         with
 146         <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 147
 148       </varlistentry>
 149
 150     </variablelist>
 151   </refsect1>
 152
 153   <xi:include href="libsystemd-pkgconfig.xml" />
 154
 155   <refsect1>
 156     <title>See Also</title>
 157
 158     <para>
 159       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 160       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 161       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 162       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 163       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 164       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 165       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 166       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 167       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 168     </para>
 169   </refsect1>
 170
 171 </refentry>