man/sd_event_new.xml

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  23
  24 <refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_new</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_new</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_new</refname>
  47     <refname>sd_event_default</refname>
  48     <refname>sd_event_ref</refname>
  49     <refname>sd_event_unref</refname>
  50     <refname>sd_event_unrefp</refname>
  51     <refname>sd_event_get_tid</refname>
  52     <refname>sd_event</refname>
  53
  54     <refpurpose>Acquire and release an event loop object</refpurpose>
  55   </refnamediv>
  56
  57   <refsynopsisdiv>
  58     <funcsynopsis>
  59       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  60
  61       <funcsynopsisinfo><token>typedef</token> struct sd_event sd_event;</funcsynopsisinfo>
  62
  63       <funcprototype>
  64         <funcdef>int <function>sd_event_new</function></funcdef>
  65         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  66       </funcprototype>
  67
  68       <funcprototype>
  69         <funcdef>int <function>sd_event_default</function></funcdef>
  70         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  71       </funcprototype>
  72
  73       <funcprototype>
  74         <funcdef>sd_event *<function>sd_event_ref</function></funcdef>
  75         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  76       </funcprototype>
  77
  78       <funcprototype>
  79         <funcdef>sd_event *<function>sd_event_unref</function></funcdef>
  80         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  81       </funcprototype>
  82
  83       <funcprototype>
  84         <funcdef>void <function>sd_event_unrefp</function></funcdef>
  85         <paramdef>sd_event **<parameter>event</parameter></paramdef>
  86       </funcprototype>
  87
  88       <funcprototype>
  89         <funcdef>int <function>sd_event_get_tid</function></funcdef>
  90         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  91         <paramdef>pid_t *<parameter>tid</parameter></paramdef>
  92       </funcprototype>
  93
  94     </funcsynopsis>
  95   </refsynopsisdiv>
  96
  97   <refsect1>
  98     <title>Description</title>
  99
 100     <para><function>sd_event_new()</function> allocates a new event
 101     loop object. The event loop object is returned in the
 102     <parameter>event</parameter> parameter. After use, drop
 103     the returned reference with
 104     <function>sd_event_unref()</function>. When the last reference is
 105     dropped, the object is freed.</para>
 106
 107     <para><function>sd_event_default()</function> acquires a reference
 108     to the default event loop object of the calling thread, possibly
 109     allocating a new object if no default event loop object has been
 110     allocated yet for the thread. After use, drop the returned
 111     reference with <function>sd_event_unref()</function>. When the
 112     last reference is dropped, the event loop is freed. If this
 113     function is called while the object returned from a previous call
 114     from the same thread is still referenced, the same object is
 115     returned again, but the reference is increased by one. It is
 116     recommended to use this call instead of
 117     <function>sd_event_new()</function> in order to share event loop
 118     objects between various components that are dispatched in the same
 119     thread. All threads have exactly either zero or one default event loop
 120     objects associated, but never more.</para>
 121
 122     <para>After allocating an event loop object, add event sources to
 123     it with
 124     <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 125     <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 126     <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 127     <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 128     or
 129     <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 130     and then execute the event loop using
 131     <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 132
 133     <para><function>sd_event_ref()</function> increases the reference
 134     count of the specified event loop object by one.</para>
 135
 136     <para><function>sd_event_unref()</function> decreases the
 137     reference count of the specified event loop object by one. If
 138     the count hits zero, the object is freed. Note that it
 139     is freed regardless of whether it is the default event loop object for a
 140     thread or not. This means that allocating an event loop with
 141     <function>sd_event_default()</function>, then releasing it, and
 142     then acquiring a new one with
 143     <function>sd_event_default()</function> will result in two
 144     distinct objects. Note that, in order to free an event loop object,
 145     all remaining event sources of the event loop also need to be
 146     freed as each keeps a reference to it.</para>
 147
 148     <para><function>sd_event_unrefp()</function> is similar to
 149     <function>sd_event_unref()</function> but takes a pointer to a
 150     pointer to an <type>sd_event</type> object. This call is useful in
 151     conjunction with GCC's and LLVM's <ulink
 152     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 153     Variable Attribute</ulink>. Note that this function is defined as
 154     inline function. Use a declaration like the following,
 155     in order to allocate an event loop object that is freed
 156     automatically as the code block is left:</para>
 157
 158     <programlisting>{
 159         __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
 160         int r;
 161         …
 162         r = sd_event_default(&amp;event);
 163         if (r &lt; 0)
 164                 fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
 165         …
 166 }</programlisting>
 167
 168     <para><function>sd_event_ref()</function>,
 169     <function>sd_event_unref()</function> and
 170     <function>sd_event_unrefp()</function> execute no operation if the
 171     passed in event loop object is <constant>NULL</constant>.</para>
 172
 173     <para><function>sd_event_get_tid()</function> retrieves the thread
 174     identifier ("TID") of the thread the specified event loop object
 175     is associated with. This call is only supported for event loops
 176     allocated with <function>sd_event_default()</function>, and
 177     returns the identifier for the thread the event loop is the
 178     default event loop of. See <citerefentry
 179     project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 180     for more information on thread identifiers.</para>
 181   </refsect1>
 182
 183   <refsect1>
 184     <title>Return Value</title>
 185
 186     <para>On success, <function>sd_event_new()</function>,
 187     <function>sd_event_default()</function> and
 188     <function>sd_event_get_tid()</function> return 0 or a positive
 189     integer. On failure, they return a negative errno-style error
 190     code. <function>sd_event_ref()</function> always returns a pointer
 191     to the event loop object passed
 192     in. <function>sd_event_unref()</function> always returns
 193     <constant>NULL</constant>.</para>
 194   </refsect1>
 195
 196   <refsect1>
 197     <title>Errors</title>
 198
 199     <para>Returned errors may indicate the following problems:</para>
 200
 201     <variablelist>
 202       <varlistentry>
 203         <term><constant>-ENOMEM</constant></term>
 204
 205         <listitem><para>Not enough memory to allocate the object.</para></listitem>
 206       </varlistentry>
 207
 208       <varlistentry>
 209         <term><constant>-EMFILE</constant></term>
 210
 211         <listitem><para>The maximum number of event loops has been allocated.</para></listitem>
 212
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><constant>-ENXIO</constant></term>
 217
 218         <listitem><para><function>sd_event_get_tid()</function> was
 219         invoked on an event loop object that was not allocated with
 220         <function>sd_event_default()</function>.</para></listitem>
 221       </varlistentry>
 222
 223     </variablelist>
 224   </refsect1>
 225
 226   <xi:include href="libsystemd-pkgconfig.xml" />
 227
 228   <refsect1>
 229     <title>See Also</title>
 230
 231     <para>
 232       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 233       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 234       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 235       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 236       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 237       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 238       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 239       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 240       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 241       <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 242       <citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 243     </para>
 244   </refsect1>
 245
 246 </refentry>