--- /dev/null
+<?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="libelogind-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>
~ianmdlvl / elogind.git / blobdiff