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systemd/man/sd_event_wait.xml
Tom Gundersen 12b42c7667 man: revert dynamic paths for split-usr setups
This did not really work out as we had hoped. Trying to do this upstream
introduced several problems that probably makes it better suited as a
downstream patch after all. At any rate, it is not releaseable in the
current state, so we at least need to revert this before the release.

 * by adjusting the path to binaries, but not do the same thing to the
   search path we end up with inconsistent man-pages. Adjusting the search
   path too would be quite messy, and it is not at all obvious that this is
   worth the effort, but at any rate it would have to be done before we
   could ship this.

 * this means that distributed man-pages does not make sense as they depend
   on config options, and for better or worse we are still distributing
   man pages, so that is something that definitely needs sorting out before
   we could ship with this patch.

 * we have long held that split-usr is only minimally supported in order
   to boot, and something we hope will eventually go away. So before we start
   adding even more magic/effort in order to make this work nicely, we should
   probably question if it makes sense at all.
2015-06-18 19:47:44 +02:00

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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
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(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
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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 &lt;systemd/sd-event.h&gt;</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>