mirror of
https://github.com/systemd/systemd
synced 2024-09-06 00:41:36 +00:00
![Lennart Poettering](/assets/img/avatar_default.png)
This extends the existing event loop iteration counter to 64bit, and exposes it via a new function sd_event_get_iteration(). This is helpful for cases like issue #3612. After all, since we maintain the counter anyway, we might as well expose it. (This also fixes an unrelated issue in the man page for sd_event_wait() where micro and milliseconds got mixed up)
357 lines
15 KiB
XML
357 lines
15 KiB
XML
<?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>
|