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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="sd_event_add_defer" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_event_add_defer</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_event_add_defer</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_event_add_defer</refname>
<refname>sd_event_add_post</refname>
<refname>sd_event_add_exit</refname>
<refname>sd_event_handler_t</refname>
<refpurpose>Add static event sources to an event loop</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
<funcprototype>
<funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_add_defer</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_add_post</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_add_exit</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>These three functions add new static event sources to an
event loop. The event loop object is specified in the
<parameter>event</parameter> parameter, the event source object is
returned in the <parameter>source</parameter> parameter. The event
sources are enabled statically and will "fire" when the event loop
is run and the conditions described below are met. The handler
function will be passed the <parameter>userdata</parameter>
pointer, which may be chosen freely by the caller.</para>
<para><function>sd_event_add_defer()</function> adds a new event
source that will be dispatched instantly, before the event loop
goes to sleep again and waits for new events. By default, the
handler will be called once
(<constant>SD_EVENT_ONESHOT</constant>). Note that if the event
source is set to <constant>SD_EVENT_ON</constant> the event loop
will never go to sleep again, but continuously call the handler,
possibly interleaved with other event sources.</para>
<para><function>sd_event_add_post()</function> adds a new event
source that is run before the event loop will sleep and wait
for new events, but only after at least one other non-post event
source was dispatched. By default, the source is enabled
permanently (<constant>SD_EVENT_ON</constant>). Note that this
event source type will still allow the event loop to go to sleep
again, even if set to <constant>SD_EVENT_ON</constant>, as long as
no other event source is ever triggered.</para>
<para><function>sd_event_add_exit()</function> adds a new event
source that will be dispatched when the event loop is terminated
with <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>The
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
function may be used to enable the event source permanently
(<constant>SD_EVENT_ON</constant>) or to make it fire just once
(<constant>SD_EVENT_ONESHOT</constant>).</para>
<para>If the handler function returns a negative error code, it
will be disabled after the invocation, even if the
<constant>SD_EVENT_ON</constant> mode was requested before.</para>
<para>To destroy an event source object use
<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
but note that the event source is only removed from the event loop
when all references to the event source are dropped. To make sure
an event source does not fire anymore, even when there's still a
reference to it kept, consider setting the event source to
<constant>SD_EVENT_OFF</constant> with
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>If the second parameter of these functions is passed as
NULL no reference to the event source object is returned. In this
case the event source is considered "floating", and will be
destroyed implicitly when the event loop itself is
destroyed.</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.</para>
</refsect1>
<refsect1>
<title>Errors</title>
<para>Returned errors may indicate the following problems:</para>
<variablelist>
<varlistentry>
<term><constant>-ENOMEM</constant></term>
<listitem><para>Not enough memory to allocate an object.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>An invalid argument has been passed.</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>
</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</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_now</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_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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