man/sd_event_wait.xml - systemd-stable - Rivoreo Source Code Repositories

 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

 <!--
   This file is part of systemd.

   Copyright 2015 Zbigniew Jędrzejewski-Szmek

   systemd is free software; you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published by
   the Free Software Foundation; either version 2.1 of the License, or
   (at your option) any later version.

   systemd is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 -->

 <refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude">

   <refentryinfo>
     <title>sd_event_wait</title>
     <productname>systemd</productname>

     <authorgroup>
       <author>
         <contrib>Developer</contrib>
         <firstname>Tom</firstname>
         <surname>Gundersen</surname>
         <email>teg@jklm.no</email>
       </author>
     </authorgroup>
   </refentryinfo>

   <refmeta>
     <refentrytitle>sd_event_wait</refentrytitle>
     <manvolnum>3</manvolnum>
   </refmeta>

   <refnamediv>
     <refname>sd_event_wait</refname>
     <refname>sd_event_prepare</refname>
     <refname>sd_event_dispatch</refname>
     <refname>sd_event_get_state</refname>
     <refname>sd_event_get_iteration</refname>
     <refname>SD_EVENT_INITIAL</refname>
     <refname>SD_EVENT_PREPARING</refname>
     <refname>SD_EVENT_ARMED</refname>
     <refname>SD_EVENT_PENDING</refname>
     <refname>SD_EVENT_RUNNING</refname>
     <refname>SD_EVENT_EXITING</refname>
     <refname>SD_EVENT_FINISHED</refname>

     <refpurpose>Low-level event loop operations</refpurpose>
   </refnamediv>

   <refsynopsisdiv>
     <funcsynopsis>
       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

       <funcsynopsisinfo><token>enum</token> {
         <constant>SD_EVENT_INITIAL</constant>,
         <constant>SD_EVENT_PREPARING</constant>,
         <constant>SD_EVENT_ARMED</constant>,
         <constant>SD_EVENT_PENDING</constant>,
         <constant>SD_EVENT_RUNNING</constant>,
         <constant>SD_EVENT_EXITING</constant>,
         <constant>SD_EVENT_FINISHED</constant>,
 };</funcsynopsisinfo>

       <funcprototype>
         <funcdef>int <function>sd_event_prepare</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
       </funcprototype>

       <funcprototype>
         <funcdef>int <function>sd_event_wait</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
         <paramdef>uint64_t <parameter>usec</parameter></paramdef>
       </funcprototype>

       <funcprototype>
         <funcdef>int <function>sd_event_dispatch</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
       </funcprototype>

       <funcprototype>
         <funcdef>int <function>sd_event_get_state</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
       </funcprototype>

       <funcprototype>
         <funcdef>int <function>sd_event_get_iteration</function></funcdef>
         <paramdef>sd_event *<parameter>event</parameter></paramdef>
         <paramdef>uint64_t *<parameter>ret</parameter></paramdef>
       </funcprototype>

     </funcsynopsis>
   </refsynopsisdiv>

   <refsect1>
     <title>Description</title>

     <para>The low-level <function>sd_event_prepare()</function>,
     <function>sd_event_wait()</function> and
     <function>sd_event_dispatch()</function> functions may be used to
     execute specific phases of an event loop. See
     <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     and
     <citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     for higher-level functions that execute individual but complete
     iterations of an event loop or run it continuously.</para>

     <para><function>sd_event_prepare()</function> checks for pending
     events and arms necessary timers. If any events are ready to be
     processed ("pending"), it returns a positive, non-zero value, and the caller
     should process these events with
     <function>sd_event_dispatch()</function>.</para>

     <para><function>sd_event_dispatch()</function> dispatches the
     highest priority event source that has a pending event. On
     success, <function>sd_event_dispatch()</function> returns either
     zero, which indicates that no further event sources may be
     dispatched and exiting of the event loop was requested via
     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>;
     or a positive non-zero value, which means that an event source was
     dispatched and the loop returned to its initial state, and the
     caller should initiate the next event loop iteration by invoking
     <function>sd_event_prepare()</function> again.</para>

     <para>In case <function>sd_event_prepare()</function> returned
     zero, <function>sd_event_wait()</function> should be called to
     wait for further events or a timeout. If any events are ready to
     be processed, it returns a positive, non-zero value, and the
     events should be dispatched with
     <function>sd_event_dispatch()</function>. Otherwise, the event
     loop returned to its initial state and the next event loop
     iteration should be initiated by invoking
     <function>sd_event_prepare()</function> again.</para>

     <para><function>sd_event_get_state()</function> may be used to
     determine the state the event loop is currently in. It returns one
     of the states described below.</para>

     <para><function>sd_event_get_iteration()</function> may be used to determine the current iteration of the event
     loop. It returns an unsigned 64bit integer containing a counter that increases monotonically with each iteration of
     the event loop, starting with 0. The counter is increased at the time of the
     <function>sd_event_prepare()</function> invocation.</para>

     <para>All five functions take, as the first argument, the event loop object <parameter>event</parameter> that has
     been created with <function>sd_event_new()</function>. The timeout for <function>sd_event_wait()</function> is
     specified in <parameter>usec</parameter> in microseconds.  <constant>(uint64_t) -1</constant> may be used to
     specify an infinite timeout.</para>
 </refsect1>

   <refsect1>
     <title>State Machine</title>

     <para>The event loop knows the following states, that may be
     queried with <function>sd_event_get_state()</function>.</para>

     <variablelist>
       <varlistentry>
         <term><constant>SD_EVENT_INITIAL</constant></term>

         <listitem><para>The initial state the event loop is in,
         before each event loop iteration. Use
         <function>sd_event_prepare()</function> to transition the
         event loop into the <constant>SD_EVENT_ARMED</constant> or
         <constant>SD_EVENT_PENDING</constant> states.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_PREPARING</constant></term>

         <listitem><para>An event source is currently being prepared,
         i.e. the preparation handler is currently being executed, as
         set with
         <citerefentry><refentrytitle>sd_event_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
         state is only seen in the event source preparation handler
         that is invoked from the
         <function>sd_event_prepare()</function> call and is
         immediately followed by <constant>SD_EVENT_ARMED</constant> or
         <constant>SD_EVENT_PENDING</constant>.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_ARMED</constant></term>

         <listitem><para><function>sd_event_prepare()</function> has
         been called and no event sources were ready to be
         dispatched. Use <function>sd_event_wait()</function> to wait
         for new events, and transition into
         <constant>SD_EVENT_PENDING</constant> or back into
         <constant>SD_EVENT_INITIAL</constant>.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_PENDING</constant></term>

         <listitem><para><function>sd_event_prepare()</function> or
         <function>sd_event_wait()</function> have been called and
         there were event sources with events pending. Use
         <function>sd_event_dispatch()</function> to dispatch the
         highest priority event source and transition back to
         <constant>SD_EVENT_INITIAL</constant>, or
         <constant>SD_EVENT_FINISHED</constant>.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_RUNNING</constant></term>

         <listitem><para>A regular event source is currently being
         dispatched. This state is only seen in the event source
         handler that is invoked from the
         <function>sd_event_dispatch()</function> call, and is
         immediately followed by <constant>SD_EVENT_INITIAL</constant>
         or <constant>SD_EVENT_FINISHED</constant> as soon the event
         source handler returns. Note that during dispatching of exit
         event sources the <constant>SD_EVENT_EXITING</constant> state
         is seen instead.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_EXITING</constant></term>

         <listitem><para>Similar to
         <constant>SD_EVENT_RUNNING</constant> but is the state in
         effect while dispatching exit event sources. It is followed by
         <constant>SD_EVENT_INITIAL</constant> or
         <constant>SD_EVENT_FINISHED</constant> as soon as the event
         handler returns.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>SD_EVENT_FINISHED</constant></term>

         <listitem><para>The event loop has exited. All exit event
         sources have run. If the event loop is in this state it serves
         no purpose anymore, and should be freed.</para></listitem>
       </varlistentry>

     </variablelist>

     <para>A simplified flow chart of the states and the calls to
     transition between them is shown below. Note that
     <constant>SD_EVENT_PREPARING</constant>,
     <constant>SD_EVENT_RUNNING</constant> and
     <constant>SD_EVENT_EXITING</constant> are not shown here.</para>

     <programlisting>
           INITIAL -&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---&lt;---\
              |                                                     |
              |                                                     ^
              |                                                     |
              v                 ret == 0                            |
       sd_event_prepare() &gt;---&gt;---&gt;---&gt;---&gt;- ARMED                  |
              |                                |                    ^
              | ret > 0                        |                    |
              |                                |                    |
              v                                v          ret == 0  |
           PENDING &lt;---&lt;---&lt;---&lt;---&lt;---&lt; sd_event_wait() &gt;---&gt;---&gt;--+
              |           ret > 0                                   ^
              |                                                     |
              |                                                     |
              v                                                     |
       sd_event_dispatch() &gt;---&gt;---&gt;---&gt;---&gt;---&gt;---&gt;---&gt;---&gt;---&gt;---&gt;/
              |                             ret > 0
              | ret == 0
              |
              v
           FINISHED
     </programlisting>
   </refsect1>

   <refsect1>
     <title>Return Value</title>

     <para>On success, these functions return 0 or a positive integer.
     On failure, they return a negative errno-style error code. In case
     of <function>sd_event_prepare()</function> and
     <function>sd_event_wait()</function>, a positive, non-zero return
     code indicates that events are ready to be processed and zero
     indicates that no events are ready. In case of
     <function>sd_event_dispatch()</function>, a positive, non-zero
     return code indicates that the event loop returned to its initial
     state and zero indicates the event loop has
     exited. <function>sd_event_get_state()</function> returns a
     positive or zero state on success.</para>
   </refsect1>

   <refsect1>
     <title>Errors</title>

     <para>Returned errors may indicate the following problems:</para>

     <variablelist>
       <varlistentry>
         <term><constant>-EINVAL</constant></term>

         <listitem><para>The <parameter>event</parameter> parameter is
         invalid or <constant>NULL</constant>.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>-EBUSY</constant></term>

         <listitem><para>The event loop object is not in the right
         state.</para></listitem>
       </varlistentry>

       <varlistentry>
         <term><constant>-ESTALE</constant></term>

         <listitem><para>The event loop is already terminated.</para></listitem>

       </varlistentry>

       <varlistentry>
         <term><constant>-ECHILD</constant></term>

         <listitem><para>The event loop has been created in a different process.</para></listitem>

       </varlistentry>

     </variablelist>

     <para>Other errors are possible, too.</para>
   </refsect1>

   <xi:include href="libsystemd-pkgconfig.xml" />

   <refsect1>
     <title>See Also</title>

     <para>
       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
       <citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     </para>
   </refsect1>

 </refentry>
	<?xml version='1.0'?> <!--- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil --->
	<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

	<!--
	This file is part of systemd.

	Copyright 2015 Zbigniew Jędrzejewski-Szmek

	systemd is free software; you can redistribute it and/or modify it
	under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation; either version 2.1 of the License, or
	(at your option) any later version.

	systemd is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with systemd; If not, see <http://www.gnu.org/licenses/>.
	-->

	<refentry id="sd_event_wait" xmlns:xi="http://www.w3.org/2001/XInclude">

	<refentryinfo>
	<title>sd_event_wait</title>
	<productname>systemd</productname>

	<authorgroup>
	<author>
	<contrib>Developer</contrib>
	<firstname>Tom</firstname>
	<surname>Gundersen</surname>
	<email>teg@jklm.no</email>
	</author>
	</authorgroup>
	</refentryinfo>

	<refmeta>
	<refentrytitle>sd_event_wait</refentrytitle>
	<manvolnum>3</manvolnum>
	</refmeta>

	<refnamediv>
	<refname>sd_event_wait</refname>
	<refname>sd_event_prepare</refname>
	<refname>sd_event_dispatch</refname>
	<refname>sd_event_get_state</refname>
	<refname>sd_event_get_iteration</refname>
	<refname>SD_EVENT_INITIAL</refname>
	<refname>SD_EVENT_PREPARING</refname>
	<refname>SD_EVENT_ARMED</refname>
	<refname>SD_EVENT_PENDING</refname>
	<refname>SD_EVENT_RUNNING</refname>
	<refname>SD_EVENT_EXITING</refname>
	<refname>SD_EVENT_FINISHED</refname>

	<refpurpose>Low-level event loop operations</refpurpose>
	</refnamediv>

	<refsynopsisdiv>
	<funcsynopsis>
	<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>

	<funcsynopsisinfo><token>enum</token> {
	<constant>SD_EVENT_INITIAL</constant>,
	<constant>SD_EVENT_PREPARING</constant>,
	<constant>SD_EVENT_ARMED</constant>,
	<constant>SD_EVENT_PENDING</constant>,
	<constant>SD_EVENT_RUNNING</constant>,
	<constant>SD_EVENT_EXITING</constant>,
	<constant>SD_EVENT_FINISHED</constant>,
	};</funcsynopsisinfo>

	<funcprototype>
	<funcdef>int <function>sd_event_prepare</function></funcdef>
	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	</funcprototype>

	<funcprototype>
	<funcdef>int <function>sd_event_wait</function></funcdef>
	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	<paramdef>uint64_t <parameter>usec</parameter></paramdef>
	</funcprototype>

	<funcprototype>
	<funcdef>int <function>sd_event_dispatch</function></funcdef>
	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	</funcprototype>

	<funcprototype>
	<funcdef>int <function>sd_event_get_state</function></funcdef>
	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	</funcprototype>

	<funcprototype>
	<funcdef>int <function>sd_event_get_iteration</function></funcdef>
	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	<paramdef>uint64_t *<parameter>ret</parameter></paramdef>
	</funcprototype>

	</funcsynopsis>
	</refsynopsisdiv>

	<refsect1>
	<title>Description</title>

	<para>The low-level <function>sd_event_prepare()</function>,
	<function>sd_event_wait()</function> and
	<function>sd_event_dispatch()</function> functions may be used to
	execute specific phases of an event loop. See
	<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>
	and
	<citerefentry><refentrytitle>sd_event_loop</refentrytitle><manvolnum>3</manvolnum></citerefentry>
	for higher-level functions that execute individual but complete
	iterations of an event loop or run it continuously.</para>

	<para><function>sd_event_prepare()</function> checks for pending
	events and arms necessary timers. If any events are ready to be
	processed ("pending"), it returns a positive, non-zero value, and the caller
	should process these events with
	<function>sd_event_dispatch()</function>.</para>

	<para><function>sd_event_dispatch()</function> dispatches the
	highest priority event source that has a pending event. On
	success, <function>sd_event_dispatch()</function> returns either
	zero, which indicates that no further event sources may be
	dispatched and exiting of the event loop was requested via
	<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>;
	or a positive non-zero value, which means that an event source was
	dispatched and the loop returned to its initial state, and the
	caller should initiate the next event loop iteration by invoking
	<function>sd_event_prepare()</function> again.</para>

	<para>In case <function>sd_event_prepare()</function> returned
	zero, <function>sd_event_wait()</function> should be called to
	wait for further events or a timeout. If any events are ready to
	be processed, it returns a positive, non-zero value, and the
	events should be dispatched with
	<function>sd_event_dispatch()</function>. Otherwise, the event
	loop returned to its initial state and the next event loop
	iteration should be initiated by invoking
	<function>sd_event_prepare()</function> again.</para>

	<para><function>sd_event_get_state()</function> may be used to
	determine the state the event loop is currently in. It returns one
	of the states described below.</para>

	<para><function>sd_event_get_iteration()</function> may be used to determine the current iteration of the event
	loop. It returns an unsigned 64bit integer containing a counter that increases monotonically with each iteration of
	the event loop, starting with 0. The counter is increased at the time of the
	<function>sd_event_prepare()</function> invocation.</para>

	<para>All five functions take, as the first argument, the event loop object <parameter>event</parameter> that has
	been created with <function>sd_event_new()</function>. The timeout for <function>sd_event_wait()</function> is
	specified in <parameter>usec</parameter> in microseconds. <constant>(uint64_t) -1</constant> may be used to
	specify an infinite timeout.</para>
	</refsect1>

	<refsect1>
	<title>State Machine</title>

	<para>The event loop knows the following states, that may be
	queried with <function>sd_event_get_state()</function>.</para>

	<variablelist>
	<varlistentry>
	<term><constant>SD_EVENT_INITIAL</constant></term>

	<listitem><para>The initial state the event loop is in,
	before each event loop iteration. Use
	<function>sd_event_prepare()</function> to transition the
	event loop into the <constant>SD_EVENT_ARMED</constant> or
	<constant>SD_EVENT_PENDING</constant> states.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_PREPARING</constant></term>

	<listitem><para>An event source is currently being prepared,
	i.e. the preparation handler is currently being executed, as
	set with
	<citerefentry><refentrytitle>sd_event_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
	state is only seen in the event source preparation handler
	that is invoked from the
	<function>sd_event_prepare()</function> call and is
	immediately followed by <constant>SD_EVENT_ARMED</constant> or
	<constant>SD_EVENT_PENDING</constant>.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_ARMED</constant></term>

	<listitem><para><function>sd_event_prepare()</function> has
	been called and no event sources were ready to be
	dispatched. Use <function>sd_event_wait()</function> to wait
	for new events, and transition into
	<constant>SD_EVENT_PENDING</constant> or back into
	<constant>SD_EVENT_INITIAL</constant>.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_PENDING</constant></term>

	<listitem><para><function>sd_event_prepare()</function> or
	<function>sd_event_wait()</function> have been called and
	there were event sources with events pending. Use
	<function>sd_event_dispatch()</function> to dispatch the
	highest priority event source and transition back to
	<constant>SD_EVENT_INITIAL</constant>, or
	<constant>SD_EVENT_FINISHED</constant>.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_RUNNING</constant></term>

	<listitem><para>A regular event source is currently being
	dispatched. This state is only seen in the event source
	handler that is invoked from the
	<function>sd_event_dispatch()</function> call, and is
	immediately followed by <constant>SD_EVENT_INITIAL</constant>
	or <constant>SD_EVENT_FINISHED</constant> as soon the event
	source handler returns. Note that during dispatching of exit
	event sources the <constant>SD_EVENT_EXITING</constant> state
	is seen instead.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_EXITING</constant></term>

	<listitem><para>Similar to
	<constant>SD_EVENT_RUNNING</constant> but is the state in
	effect while dispatching exit event sources. It is followed by
	<constant>SD_EVENT_INITIAL</constant> or
	<constant>SD_EVENT_FINISHED</constant> as soon as the event
	handler returns.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>SD_EVENT_FINISHED</constant></term>

	<listitem><para>The event loop has exited. All exit event
	sources have run. If the event loop is in this state it serves
	no purpose anymore, and should be freed.</para></listitem>
	</varlistentry>

	</variablelist>

	<para>A simplified flow chart of the states and the calls to
	transition between them is shown below. Note that
	<constant>SD_EVENT_PREPARING</constant>,
	<constant>SD_EVENT_RUNNING</constant> and
	<constant>SD_EVENT_EXITING</constant> are not shown here.</para>

	<programlisting>
	INITIAL -<---<---<---<---<---<---<---<---<---<---<---<---\
	\| \|
	\| ^
	\| \|
	v ret == 0 \|
	sd_event_prepare() >--->--->--->--->- ARMED \|
	\| \| ^
	\| ret > 0 \| \|
	\| \| \|
	v v ret == 0 \|
	PENDING <---<---<---<---<---< sd_event_wait() >--->--->--+
	\| ret > 0 ^
	\| \|
	\| \|
	v \|
	sd_event_dispatch() >--->--->--->--->--->--->--->--->--->--->/
	\| ret > 0
	\| ret == 0
	\|
	v
	FINISHED
	</programlisting>
	</refsect1>

	<refsect1>
	<title>Return Value</title>

	<para>On success, these functions return 0 or a positive integer.
	On failure, they return a negative errno-style error code. In case
	of <function>sd_event_prepare()</function> and
	<function>sd_event_wait()</function>, a positive, non-zero return
	code indicates that events are ready to be processed and zero
	indicates that no events are ready. In case of
	<function>sd_event_dispatch()</function>, a positive, non-zero
	return code indicates that the event loop returned to its initial
	state and zero indicates the event loop has
	exited. <function>sd_event_get_state()</function> returns a
	positive or zero state on success.</para>
	</refsect1>

	<refsect1>
	<title>Errors</title>

	<para>Returned errors may indicate the following problems:</para>

	<variablelist>
	<varlistentry>
	<term><constant>-EINVAL</constant></term>

	<listitem><para>The <parameter>event</parameter> parameter is
	invalid or <constant>NULL</constant>.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>-EBUSY</constant></term>

	<listitem><para>The event loop object is not in the right
	state.</para></listitem>
	</varlistentry>

	<varlistentry>
	<term><constant>-ESTALE</constant></term>

	<listitem><para>The event loop is already terminated.</para></listitem>

	</varlistentry>

	<varlistentry>
	<term><constant>-ECHILD</constant></term>

	<listitem><para>The event loop has been created in a different process.</para></listitem>

	</varlistentry>

	</variablelist>

	<para>Other errors are possible, too.</para>
	</refsect1>

	<xi:include href="libsystemd-pkgconfig.xml" />

	<refsect1>
	<title>See Also</title>

	<para>
	<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_get_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	<citerefentry><refentrytitle>sd_event_source_set_prepare</refentrytitle><manvolnum>3</manvolnum></citerefentry>
	</para>
	</refsect1>

	</refentry>