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diff --git a/src/libsystemd/sd_event_wait.xml b/src/libsystemd/sd_event_wait.xml new file mode 100644 index 0000000000..26327dc688 --- /dev/null +++ b/src/libsystemd/sd_event_wait.xml @@ -0,0 +1,356 @@ +<?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="libsystemd-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> |