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<?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" conditional="ENABLE_KDBUS">
<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>
<refpurpose>Run parts of libsystemd event loop</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-event.h></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>timeout</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_dispatch</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>Functions described here form parts of an event loop.</para>
<para><function>sd_event_prepare</function> checks for pending
events and arms necessary timers. If any events are ready to be
processed, it returns a positive value, and the events should be
processed with <function>sd_event_dispatch</function>.
<function>sd_event_dispatch</function> runs a handler for one of
the events from the sources with the highest priority. On success,
<function>sd_event_dispatch</function> returns either 0, which
means that the loop is finished, or a positive value, which means
that the loop is again in the initial state and
<function>sd_event_prepare</function> should be called again.
</para>
<para>In case <function>sd_event_prepare</function> returned 0,
<function>sd_event_wait</function> should be called to wait for
events or a timeout. If any events are ready to be processed, it
returns a positive value, and the events should be processed with
<function>sd_event_dispatch</function>. Otherwise, the loop is
back in the inital state and <function>sd_event_prepare</function>
should be called again.</para>
<programlisting>
┌──────────┐
│ initial ├──←←←←←←←←←←←←←←←←←←←─┐
└───┬──────┘ ↑
│ ↑
sd_event_prepare ┌─────────┐ ↑
├ 0 →→→→→→→──┤ armed │ ↑
1 └───┬─────┘ ↑
↓ │ ↑
↓ sd_event_wait ↑
├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘
┌───┴──────┐ ↑
│ pending │ ↑
└───┬──────┘ ↑
│ ↑
sd_event_dispatch ↑
↓ ↑
├ 1 ──────────→→→→→→→─────────┘
0
↓
┌───┴──────┐
│ finished │
└──────────┘
</programlisting>
<para>All three functions as the first argument take the event
loop object <parameter>event</parameter> that is created with with
<function>sd_event_new</function>. The timeout for
<function>sd_event_wait</function> is specified with
<parameter>timeout</parameter> in milliseconds.
<constant>(uint64_t) -1</constant> may be used to specify an
infinite timeout.</para>
</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 value means that
events are ready to be processed and 0 means that no events are
ready. In case of <function>sd_event_dispatch</function> a
positive value means that the loop is again in the initial state
and 0 means the loop is finished. For any of those functions, a
negative return value means the loop must be aborted.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>Parameter <parameter>event</parameter> is
<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>
<refsect1>
<title>Notes</title>
<para>Functions described here are available
as a shared library, which can be compiled and linked to with the
<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<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_run</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>.
</para>
</refsect1>
</refentry>
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