<?xml version='1.0'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <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.</para> <para>The <parameter>handler</parameter> is a function to call or <constant>NULL</constant>. The handler function will be passed the <parameter>userdata</parameter> pointer, which may be chosen freely by the caller. The handler may return negative to signal an error (see below), other return values are ignored. If <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be used.</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 either be disabled after the invocation, even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to terminate, see <citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>. </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 <constant>NULL</constant> 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> <para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_defer()</function> or <function>sd_event_add_post()</function> is <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as the exit code parameter to <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Similar functionality is not available for <function>sd_event_add_exit()</function>, as these types of event sources are only dispatched when exiting anyway.</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> <refsect2> <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, library or module instance.</para></listitem> </varlistentry> </variablelist> </refsect2> </refsect1> <xi:include href="libsystemd-pkgconfig.xml" /> <refsect1> <title>History</title> <para><function>sd_event_add_defer()</function>, <function>sd_event_add_post()</function>, <function>sd_event_add_exit()</function>, and <function>sd_event_handler_t()</function> were added in version 217.</para> </refsect1> <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_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>