man/sd_event_source_unref.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/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="sd_event_source_unref" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_event_source_unref</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_event_source_unref</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_event_source_unref</refname>
  20     <refname>sd_event_source_unrefp</refname>
  21     <refname>sd_event_source_ref</refname>
  22     <refname>sd_event_source_disable_unref</refname>
  23     <refname>sd_event_source_disable_unrefp</refname>
  24
  25     <refpurpose>Increase or decrease event source reference counters</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  31
  32       <funcprototype>
  33         <funcdef>sd_event_source* <function>sd_event_source_unref</function></funcdef>
  34         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  35       </funcprototype>
  36
  37       <funcprototype>
  38         <funcdef>void <function>sd_event_source_unrefp</function></funcdef>
  39         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  40       </funcprototype>
  41
  42       <funcprototype>
  43         <funcdef>sd_event_source* <function>sd_event_source_ref</function></funcdef>
  44         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  45       </funcprototype>
  46
  47       <funcprototype>
  48         <funcdef>sd_event_source* <function>sd_event_source_disable_unref</function></funcdef>
  49         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>void <function>sd_event_source_disable_unrefp</function></funcdef>
  54         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  55       </funcprototype>
  56     </funcsynopsis>
  57   </refsynopsisdiv>
  58
  59   <refsect1>
  60     <title>Description</title>
  61
  62     <para><function>sd_event_source_unref()</function> may be used to decrement by one the internal reference
  63     counter of the event source object specified as <parameter>source</parameter>. The reference counter is
  64     initially set to one, when the event source is created with calls such as
  65     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
  66     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. When
  67     the reference counter reaches zero, the object is detached from the event loop object and destroyed.
  68     </para>
  69
  70     <para><function>sd_event_source_unrefp()</function> is similar to
  71     <function>sd_event_source_unref()</function> but takes a pointer to a
  72     pointer to an <type>sd_event_source</type> object. This call is useful in
  73     conjunction with GCC's and LLVM's <ulink
  74     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
  75     Variable Attribute</ulink>. Note that this function is defined as
  76     inline function.</para>
  77
  78     <para><function>sd_event_source_ref()</function> may be used to increase by one the internal reference
  79     counter of the event source object specified as <parameter>source</parameter>.</para>
  80
  81     <para><function>sd_event_source_unref()</function>,
  82     <function>sd_bus_creds_unrefp()</function> and
  83     <function>sd_bus_creds_ref()</function> execute no operation if
  84     the passed event source object is
  85     <constant>NULL</constant>.</para>
  86
  87     <para>Note that event source objects stay alive and may be dispatched as long as they have a reference
  88     counter greater than zero. In order to drop a reference of an event source and make sure the associated
  89     event source handler function is not called anymore it is recommended to combine a call of
  90     <function>sd_event_source_unref()</function> with a prior call to
  91     <function>sd_event_source_set_enabled()</function> with <constant>SD_EVENT_OFF</constant> or call
  92     <function>sd_event_source_disable_unref()</function>, see below.</para>
  93
  94     <para><function>sd_event_source_disable_unref()</function> combines a call to
  95     <function>sd_event_source_set_enabled()</function> with <constant>SD_EVENT_OFF</constant> with
  96     <function>sd_event_source_unref()</function>. This ensures that the source is disabled before the local
  97     reference to it is lost. The <parameter>source</parameter> parameter is allowed to be
  98     <constant>NULL</constant>.</para>
  99
 100     <para><function>sd_event_source_disable_unrefp()</function> is similar to
 101     <function>sd_event_source_unrefp()</function>, but in addition disables the source first. This call is
 102     useful in conjunction with GCC's and LLVM's
 103     <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable
 104     Attribute</ulink>. Note that this function is defined as inline function.</para>
 105   </refsect1>
 106
 107   <refsect1>
 108     <title>Return Value</title>
 109
 110     <para><function>sd_event_source_unref()</function> and
 111     <function>sd_event_source_disable_unref()</function> always return <constant>NULL</constant>.
 112     <function>sd_event_source_ref()</function> always returns the event source object passed in.</para>
 113   </refsect1>
 114
 115   <xi:include href="libsystemd-pkgconfig.xml" />
 116
 117   <refsect1>
 118     <title>History</title>
 119     <para><function>sd_event_source_unref()</function>,
 120     <function>sd_event_source_unrefp()</function>, and
 121     <function>sd_event_source_ref()</function> were added in version 229.</para>
 122     <para><function>sd_event_source_disable_unref()</function> and
 123     <function>sd_event_source_disable_unrefp()</function> were added in version 243.</para>
 124   </refsect1>
 125
 126   <refsect1>
 127     <title>See Also</title>
 128
 129     <para><simplelist type="inline">
 130       <member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 131       <member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 132       <member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 133       <member><citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 134       <member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 135       <member><citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 136       <member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 137       <member><citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 138     </simplelist></para>
 139   </refsect1>
 140
 141 </refentry>