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Also, document this functionality more prominently, including with a reference from sd_event_exit(). This is mostly to make things complete, as previously we supported NULL callbacks only in _add_time() and _add_signal(). However, I think this makes snese for IO event sources too (think: when some fd such as a pipe end sees SIGHUP or so, exit), as well as defer or post event sources (i.e. exit once we got nothing else to do). This also adds support for inotify event sources, simply to complete things (I can't see the immediate use, but maybe someone else comes up with it). The only event source type that doesn't allow callback=NULL now are exit callbacks, but for them they make little sense, as the event loop is exiting then anyway.
198 lines
9.2 KiB
XML
198 lines
9.2 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_event_add_defer" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_defer</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_add_defer</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_add_defer</refname>
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<refname>sd_event_add_post</refname>
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<refname>sd_event_add_exit</refname>
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<refname>sd_event_handler_t</refname>
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<refpurpose>Add static event sources to an event loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_defer</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_post</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_exit</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>sd_event_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>These three functions add new static event sources to an
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event loop. The event loop object is specified in the
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<parameter>event</parameter> parameter, the event source object is
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returned in the <parameter>source</parameter> parameter. The event
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sources are enabled statically and will "fire" when the event loop
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is run and the conditions described below are met. The handler
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function will be passed the <parameter>userdata</parameter>
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pointer, which may be chosen freely by the caller.</para>
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<para><function>sd_event_add_defer()</function> adds a new event
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source that will be dispatched instantly, before the event loop
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goes to sleep again and waits for new events. By default, the
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handler will be called once
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(<constant>SD_EVENT_ONESHOT</constant>). Note that if the event
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source is set to <constant>SD_EVENT_ON</constant> the event loop
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will never go to sleep again, but continuously call the handler,
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possibly interleaved with other event sources.</para>
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<para><function>sd_event_add_post()</function> adds a new event
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source that is run before the event loop will sleep and wait
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for new events, but only after at least one other non-post event
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source was dispatched. By default, the source is enabled
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permanently (<constant>SD_EVENT_ON</constant>). Note that this
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event source type will still allow the event loop to go to sleep
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again, even if set to <constant>SD_EVENT_ON</constant>, as long as
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no other event source is ever triggered.</para>
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<para><function>sd_event_add_exit()</function> adds a new event
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source that will be dispatched when the event loop is terminated
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with <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>The
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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function may be used to enable the event source permanently
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(<constant>SD_EVENT_ON</constant>) or to make it fire just once
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(<constant>SD_EVENT_ONESHOT</constant>).</para>
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<para>If the handler function returns a negative error code, it
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will be disabled after the invocation, even if the
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<constant>SD_EVENT_ON</constant> mode was requested before.</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but note that the event source is only removed from the event loop
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when all references to the event source are dropped. To make sure
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an event source does not fire anymore, even when there's still a
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reference to it kept, consider setting the event source to
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<constant>SD_EVENT_OFF</constant> with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the second parameter of these functions is passed as <constant>NULL</constant> no reference to
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the event source object is returned. In this case the event source is considered "floating", and will be
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destroyed implicitly when the event loop itself is destroyed.</para>
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<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_defer()</function> or
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<function>sd_event_add_post()</function> is <constant>NULL</constant>, and the event source fires, this
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will be considered a request to exit the event loop. In this case, the <parameter>userdata</parameter>
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parameter, cast to an integer, is passed as the exit code parameter to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Similar
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functionality is not available for <function>sd_event_add_exit()</function>, as these types of event
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sources are only dispatched when exiting anyway.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The event loop is already terminated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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