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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
217 lines
9.5 KiB
XML
217 lines
9.5 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_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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</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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<citerefentry><refentrytitle>sd_event_add_inotify</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> or
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<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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and then execute the event loop using
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<citerefentry><refentrytitle>sd_event_loop</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>, <function>sd_event_default()</function> and
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<function>sd_event_get_tid()</function> return 0 or a positive integer. On failure, they return a
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negative errno-style error code. <function>sd_event_ref()</function> always returns a pointer to the
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event loop object passed in. <function>sd_event_unref()</function> always returns
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<constant>NULL</constant>.</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 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 invoked on an event loop object that
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was not allocated with <function>sd_event_default()</function>.</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_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_add_defer</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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