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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_event_add_defer" xmlns:xi="http://www.w3.org/2001/XInclude">

<refentryinfo>

<title>sd_event_add_defer</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>More text</contrib>

<firstname>Zbigniew</firstname>

<surname>Jędrzejewski-Szmek</surname>

<email>zbyszek@in.waw.pl</email>

</author>

</authorgroup>

</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 &lt;systemd/sd-event.h&gt;</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, this 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_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>