<?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"> <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 initial 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>