mirror of
https://github.com/systemd/systemd.git
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11a1589223
Files which are installed as-is (any .service and other unit files, .conf files, .policy files, etc), are left as is. My assumption is that SPDX identifiers are not yet that well known, so it's better to retain the extended header to avoid any doubt. I also kept any copyright lines. We can probably remove them, but it'd nice to obtain explicit acks from all involved authors before doing that.
236 lines
9.6 KiB
XML
236 lines
9.6 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2014 Lennart Poettering
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-->
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<refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_new</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_new</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_new</refname>
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<refname>sd_event_default</refname>
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<refname>sd_event_ref</refname>
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<refname>sd_event_unref</refname>
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<refname>sd_event_unrefp</refname>
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<refname>sd_event_get_tid</refname>
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<refname>sd_event</refname>
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<refpurpose>Acquire and release an event loop object</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 sd_event;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_event_new</function></funcdef>
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<paramdef>sd_event **<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_default</function></funcdef>
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<paramdef>sd_event **<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_event *<function>sd_event_ref</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_event *<function>sd_event_unref</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_event_unrefp</function></funcdef>
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<paramdef>sd_event **<parameter>event</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_get_tid</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>pid_t *<parameter>tid</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><function>sd_event_new()</function> allocates a new event
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loop object. The event loop object is returned in the
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<parameter>event</parameter> parameter. After use, drop
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the returned reference with
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<function>sd_event_unref()</function>. When the last reference is
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dropped, the object is freed.</para>
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<para><function>sd_event_default()</function> acquires a reference
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to the default event loop object of the calling thread, possibly
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allocating a new object if no default event loop object has been
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allocated yet for the thread. After use, drop the returned
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reference with <function>sd_event_unref()</function>. When the
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last reference is dropped, the event loop is freed. If this
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function is called while the object returned from a previous call
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from the same thread is still referenced, the same object is
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returned again, but the reference is increased by one. It is
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recommended to use this call instead of
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<function>sd_event_new()</function> in order to share event loop
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objects between various components that are dispatched in the same
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thread. All threads have exactly either zero or one default event loop
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objects associated, but never more.</para>
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<para>After allocating an event loop object, add event sources to
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it with
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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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or
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<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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and then execute the event loop using
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<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para><function>sd_event_ref()</function> increases the reference
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count of the specified event loop object by one.</para>
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<para><function>sd_event_unref()</function> decreases the
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reference count of the specified event loop object by one. If
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the count hits zero, the object is freed. Note that it
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is freed regardless of whether it is the default event loop object for a
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thread or not. This means that allocating an event loop with
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<function>sd_event_default()</function>, then releasing it, and
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then acquiring a new one with
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<function>sd_event_default()</function> will result in two
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distinct objects. Note that, in order to free an event loop object,
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all remaining event sources of the event loop also need to be
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freed as each keeps a reference to it.</para>
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<para><function>sd_event_unrefp()</function> is similar to
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<function>sd_event_unref()</function> but takes a pointer to a
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pointer to an <type>sd_event</type> object. This call is useful in
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conjunction with GCC's and LLVM's <ulink
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url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
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Variable Attribute</ulink>. Note that this function is defined as
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inline function. Use a declaration like the following,
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in order to allocate an event loop object that is freed
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automatically as the code block is left:</para>
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<programlisting>{
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__attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
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int r;
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…
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r = sd_event_default(&event);
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if (r < 0)
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fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
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…
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}</programlisting>
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<para><function>sd_event_ref()</function>,
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<function>sd_event_unref()</function> and
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<function>sd_event_unrefp()</function> execute no operation if the
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passed in event loop object is <constant>NULL</constant>.</para>
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<para><function>sd_event_get_tid()</function> retrieves the thread
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identifier ("TID") of the thread the specified event loop object
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is associated with. This call is only supported for event loops
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allocated with <function>sd_event_default()</function>, and
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returns the identifier for the thread the event loop is the
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default event loop of. See <citerefentry
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project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for more information on thread identifiers.</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, <function>sd_event_new()</function>,
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<function>sd_event_default()</function> and
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<function>sd_event_get_tid()</function> return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code. <function>sd_event_ref()</function> always returns a pointer
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to the event loop object passed
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in. <function>sd_event_unref()</function> always returns
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<constant>NULL</constant>.</para>
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</refsect1>
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<refsect1>
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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 the object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EMFILE</constant></term>
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<listitem><para>The maximum number of event loops has been allocated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENXIO</constant></term>
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<listitem><para><function>sd_event_get_tid()</function> was
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invoked on an event loop object that was not allocated with
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<function>sd_event_default()</function>.</para></listitem>
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</varlistentry>
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</variablelist>
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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_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_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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