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/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   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
  63     decrement by one the reference counter of the event source object
  64     specified as <parameter>source</parameter>. The reference counter
  65     is initially set to one, when the event source is created with calls
  66     such as
  67     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  68     or
  69     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>. When
  70     the reference counter reaches zero it is removed from its event loop
  71     object and destroyed.</para>
  72
  73     <para><function>sd_event_source_unrefp()</function> is similar to
  74     <function>sd_event_source_unref()</function> but takes a pointer to a
  75     pointer to an <type>sd_event_source</type> object. This call is useful in
  76     conjunction with GCC's and LLVM's <ulink
  77     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
  78     Variable Attribute</ulink>. Note that this function is defined as
  79     inline function.</para>
  80
  81     <para><function>sd_event_source_ref()</function> may be used
  82     to increase by one the reference counter of the event source object
  83     specified as <parameter>source</parameter>.</para>
  84
  85     <para><function>sd_event_source_unref()</function>,
  86     <function>sd_bus_creds_unrefp()</function> and
  87     <function>sd_bus_creds_ref()</function> execute no operation if
  88     the passed event source object is
  89     <constant>NULL</constant>.</para>
  90
  91     <para>Note that event source objects stay alive and may be dispatched as long as they have a reference
  92     counter greater than zero. In order to drop a reference of an event source and make sure the associated
  93     event source handler function is not called anymore it is recommended to combine a call of
  94     <function>sd_event_source_unref()</function> with a prior call to
  95     <function>sd_event_source_set_enabled()</function> with <constant>SD_EVENT_OFF</constant> or call
  96     <function>sd_event_source_disable_unref()</function>, see below.</para>
  97
  98     <para><function>sd_event_source_disable_unref()</function> combines a call to
  99     <function>sd_event_source_set_enabled()</function> with <constant>SD_EVENT_OFF</constant> with
 100     <function>sd_event_source_unref()</function>. This ensures that the source is disabled before the local
 101     reference to it is lost. The <parameter>source</parameter> parameter is allowed to be
 102     <constant>NULL</constant>.</para>
 103
 104     <para><function>sd_event_source_disable_unrefp()</function> is similar to
 105     <function>sd_event_source_unrefp()</function>, but in addition disables the source first. This call is
 106     useful in conjunction with GCC's and LLVM's
 107     <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable
 108     Attribute</ulink>. Note that this function is defined as inline function.</para>
 109   </refsect1>
 110
 111   <refsect1>
 112     <title>Return Value</title>
 113
 114     <para><function>sd_event_source_unref()</function> and
 115     <function>sd_event_source_disable_unref()</function> always return <constant>NULL</constant>.
 116     <function>sd_event_source_ref()</function> always returns the event source object passed in.</para>
 117   </refsect1>
 118
 119   <xi:include href="libsystemd-pkgconfig.xml" />
 120
 121   <refsect1>
 122     <title>See Also</title>
 123
 124     <para>
 125       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 126       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 127       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 128       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 129       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 130       <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 131       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 132       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 133     </para>
 134   </refsect1>
 135
 136 </refentry>