214 lines
8.3 KiB
XML
214 lines
8.3 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2015 Zbigniew Jędrzejewski-Szmek
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_event_wait">
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<refentryinfo>
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<title>sd_event_wait</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Tom</firstname>
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<surname>Gundersen</surname>
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<email>teg@jklm.no</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_wait</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_wait</refname>
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<refname>sd_event_prepare</refname>
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<refname>sd_event_dispatch</refname>
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<refpurpose>Run parts of the libsystemd event loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_event_prepare</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_wait</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>uint64_t <parameter>timeout</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_dispatch</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>Functions described here form parts of an event loop.</para>
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<para><function>sd_event_prepare</function> checks for pending
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events and arms necessary timers. If any events are ready to be
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processed, it returns a positive value, and the events should be
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processed with <function>sd_event_dispatch</function>.
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<function>sd_event_dispatch</function> runs a handler for one of
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the events from the sources with the highest priority. On success,
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<function>sd_event_dispatch</function> returns either 0, which
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means that the loop is finished, or a positive value, which means
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that the loop is again in the initial state and
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<function>sd_event_prepare</function> should be called again.
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</para>
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<para>In case <function>sd_event_prepare</function> returned 0,
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<function>sd_event_wait</function> should be called to wait for
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events or a timeout. If any events are ready to be processed, it
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returns a positive value, and the events should be processed with
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<function>sd_event_dispatch</function>. Otherwise, the loop is
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back in the initial state and <function>sd_event_prepare</function>
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should be called again.</para>
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<programlisting>
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┌──────────┐
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│ initial ├──←←←←←←←←←←←←←←←←←←←─┐
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└───┬──────┘ ↑
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│ ↑
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sd_event_prepare ┌─────────┐ ↑
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├ 0 →→→→→→→──┤ armed │ ↑
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1 └───┬─────┘ ↑
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↓ │ ↑
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↓ sd_event_wait ↑
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├───←←←←←←←─── 1 ┴─ 0 →→→→→→→─┘
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┌───┴──────┐ ↑
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│ pending │ ↑
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└───┬──────┘ ↑
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│ ↑
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sd_event_dispatch ↑
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↓ ↑
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├ 1 ──────────→→→→→→→─────────┘
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0
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↓
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┌───┴──────┐
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│ finished │
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└──────────┘
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</programlisting>
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<para>All three functions take, as the first argument, the event
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loop object <parameter>event</parameter> that is created with
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<function>sd_event_new</function>. The timeout for
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<function>sd_event_wait</function> is specified with
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<parameter>timeout</parameter> in milliseconds.
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<constant>(uint64_t) -1</constant> may be used to specify an
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infinite timeout.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive integer.
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On failure, they return a negative errno-style error code. In case
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of <function>sd_event_prepare</function> and
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<function>sd_event_wait</function>, a positive value means that
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events are ready to be processed and 0 means that no events are
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ready. In case of <function>sd_event_dispatch</function>, a
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positive value means that the loop is again in the initial state
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and 0 means the loop is finished. For any of these functions, a
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negative return value means the loop must be aborted.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>The <parameter>event</parameter> parameter is
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<constant>NULL</constant>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EBUSY</constant></term>
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<listitem><para>The event loop object is not in the right
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state.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>Other errors are possible, too.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>Functions described here are available
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as a shared library, which can be compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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</refsect1>
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</refentry>
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