man/sd_event_new.xml

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  10   Copyright 2014 Lennart Poettering
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  25
  26 <refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude">
  27
  28   <refentryinfo>
  29     <title>sd_event_new</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_event_new</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_event_new</refname>
  49     <refname>sd_event_default</refname>
  50     <refname>sd_event_ref</refname>
  51     <refname>sd_event_unref</refname>
  52     <refname>sd_event_unrefp</refname>
  53     <refname>sd_event_get_tid</refname>
  54     <refname>sd_event</refname>
  55
  56     <refpurpose>Acquire and release an event loop object</refpurpose>
  57   </refnamediv>
  58
  59   <refsynopsisdiv>
  60     <funcsynopsis>
  61       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  62
  63       <funcsynopsisinfo><token>typedef</token> struct sd_event sd_event;</funcsynopsisinfo>
  64
  65       <funcprototype>
  66         <funcdef>int <function>sd_event_new</function></funcdef>
  67         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>int <function>sd_event_default</function></funcdef>
  72         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  73       </funcprototype>
  74
  75       <funcprototype>
  76         <funcdef>sd_event *<function>sd_event_ref</function></funcdef>
  77         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  78       </funcprototype>
  79
  80       <funcprototype>
  81         <funcdef>sd_event *<function>sd_event_unref</function></funcdef>
  82         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  83       </funcprototype>
  84
  85       <funcprototype>
  86         <funcdef>void <function>sd_event_unrefp</function></funcdef>
  87         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  88       </funcprototype>
  89
  90       <funcprototype>
  91         <funcdef>int <function>sd_event_get_tid</function></funcdef>
  92         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  93         <paramdef>pid_t *<parameter>tid</parameter></paramdef>
  94       </funcprototype>
  95
  96     </funcsynopsis>
  97   </refsynopsisdiv>
  98
  99   <refsect1>
 100     <title>Description</title>
 101
 102     <para><function>sd_event_new()</function> allocates a new event
 103     loop object. The event loop object is returned in the
 104     <parameter>event</parameter> parameter. After use, drop
 105     the returned reference with
 106     <function>sd_event_unref()</function>. When the last reference is
 107     dropped, the object is freed.</para>
 108
 109     <para><function>sd_event_default()</function> acquires a reference
 110     to the default event loop object of the calling thread, possibly
 111     allocating a new object if no default event loop object has been
 112     allocated yet for the thread. After use, drop the returned
 113     reference with <function>sd_event_unref()</function>. When the
 114     last reference is dropped, the event loop is freed. If this
 115     function is called while the object returned from a previous call
 116     from the same thread is still referenced, the same object is
 117     returned again, but the reference is increased by one. It is
 118     recommended to use this call instead of
 119     <function>sd_event_new()</function> in order to share event loop
 120     objects between various components that are dispatched in the same
 121     thread. All threads have exactly either zero or one default event loop
 122     objects associated, but never more.</para>
 123
 124     <para>After allocating an event loop object, add event sources to
 125     it with
 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     or
 131     <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 132     and then execute the event loop using
 133     <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 134
 135     <para><function>sd_event_ref()</function> increases the reference
 136     count of the specified event loop object by one.</para>
 137
 138     <para><function>sd_event_unref()</function> decreases the
 139     reference count of the specified event loop object by one. If
 140     the count hits zero, the object is freed. Note that it
 141     is freed regardless of whether it is the default event loop object for a
 142     thread or not. This means that allocating an event loop with
 143     <function>sd_event_default()</function>, then releasing it, and
 144     then acquiring a new one with
 145     <function>sd_event_default()</function> will result in two
 146     distinct objects. Note that, in order to free an event loop object,
 147     all remaining event sources of the event loop also need to be
 148     freed as each keeps a reference to it.</para>
 149
 150     <para><function>sd_event_unrefp()</function> is similar to
 151     <function>sd_event_unref()</function> but takes a pointer to a
 152     pointer to an <type>sd_event</type> object. This call is useful in
 153     conjunction with GCC's and LLVM's <ulink
 154     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 155     Variable Attribute</ulink>. Note that this function is defined as
 156     inline function. Use a declaration like the following,
 157     in order to allocate an event loop object that is freed
 158     automatically as the code block is left:</para>
 159
 160     <programlisting>{
 161         __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
 162         int r;
 163         …
 164         r = sd_event_default(&amp;event);
 165         if (r &lt; 0)
 166                 fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
 167         …
 168 }</programlisting>
 169
 170     <para><function>sd_event_ref()</function>,
 171     <function>sd_event_unref()</function> and
 172     <function>sd_event_unrefp()</function> execute no operation if the
 173     passed in event loop object is <constant>NULL</constant>.</para>
 174
 175     <para><function>sd_event_get_tid()</function> retrieves the thread
 176     identifier ("TID") of the thread the specified event loop object
 177     is associated with. This call is only supported for event loops
 178     allocated with <function>sd_event_default()</function>, and
 179     returns the identifier for the thread the event loop is the
 180     default event loop of. See <citerefentry
 181     project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 182     for more information on thread identifiers.</para>
 183   </refsect1>
 184
 185   <refsect1>
 186     <title>Return Value</title>
 187
 188     <para>On success, <function>sd_event_new()</function>,
 189     <function>sd_event_default()</function> and
 190     <function>sd_event_get_tid()</function> return 0 or a positive
 191     integer. On failure, they return a negative errno-style error
 192     code. <function>sd_event_ref()</function> always returns a pointer
 193     to the event loop object passed
 194     in. <function>sd_event_unref()</function> always returns
 195     <constant>NULL</constant>.</para>
 196   </refsect1>
 197
 198   <refsect1>
 199     <title>Errors</title>
 200
 201     <para>Returned errors may indicate the following problems:</para>
 202
 203     <variablelist>
 204       <varlistentry>
 205         <term><constant>-ENOMEM</constant></term>
 206
 207         <listitem><para>Not enough memory to allocate the object.</para></listitem>
 208       </varlistentry>
 209
 210       <varlistentry>
 211         <term><constant>-EMFILE</constant></term>
 212
 213         <listitem><para>The maximum number of event loops has been allocated.</para></listitem>
 214
 215       </varlistentry>
 216
 217       <varlistentry>
 218         <term><constant>-ENXIO</constant></term>
 219
 220         <listitem><para><function>sd_event_get_tid()</function> was
 221         invoked on an event loop object that was not allocated with
 222         <function>sd_event_default()</function>.</para></listitem>
 223       </varlistentry>
 224
 225     </variablelist>
 226   </refsect1>
 227
 228   <xi:include href="libsystemd-pkgconfig.xml" />
 229
 230   <refsect1>
 231     <title>See Also</title>
 232
 233     <para>
 234       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 235       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 236       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 237       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 238       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 239       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 240       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 241       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 242       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 243       <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 244       <citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 245     </para>
 246   </refsect1>
 247
 248 </refentry>