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<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_event_new</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_event_new</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_event_new</refname>
<refname>sd_event_default</refname>
<refname>sd_event_ref</refname>
<refname>sd_event_unref</refname>
<refname>sd_event_unrefp</refname>
<refname>sd_event_get_tid</refname>
<refname>sd_event</refname>
<refpurpose>Acquire and release an event loop object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
<funcsynopsisinfo><token>typedef</token> struct sd_event sd_event;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_event_new</function></funcdef>
<paramdef>sd_event **<parameter>event</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_default</function></funcdef>
<paramdef>sd_event **<parameter>event</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>sd_event *<function>sd_event_ref</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>sd_event *<function>sd_event_unref</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sd_event_unrefp</function></funcdef>
<paramdef>sd_event **<parameter>event</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_event_get_tid</function></funcdef>
<paramdef>sd_event *<parameter>event</parameter></paramdef>
<paramdef>pid_t *<parameter>tid</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_event_new()</function> allocates a new event
loop object. The event loop object is returned in the
<parameter>event</parameter> parameter. After use, drop
the returned reference with
<function>sd_event_unref()</function>. When the last reference is
dropped, the object is freed.</para>
<para><function>sd_event_default()</function> acquires a reference
to the default event loop object of the calling thread, possibly
allocating a new object if no default event loop object has been
allocated yet for the thread. After use, drop the returned
reference with <function>sd_event_unref()</function>. When the
last reference is dropped, the event loop is freed. If this
function is called while the object returned from a previous call
from the same thread is still referenced, the same object is
returned again, but the reference is increased by one. It is
recommended to use this call instead of
<function>sd_event_new()</function> in order to share event loop
objects between various components that are dispatched in the same
thread. All threads have exactly either zero or one default event loop
objects associated, but never more.</para>
<para>After allocating an event loop object, add event sources to
it with
<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>
or
<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
and then execute the event loop using
<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para><function>sd_event_ref()</function> increases the reference
count of the specified event loop object by one.</para>
<para><function>sd_event_unref()</function> decreases the
reference count of the specified event loop object by one. If
the count hits zero, the object is freed. Note that it
is freed regardless of whether it is the default event loop object for a
thread or not. This means that allocating an event loop with
<function>sd_event_default()</function>, then releasing it, and
then acquiring a new one with
<function>sd_event_default()</function> will result in two
distinct objects. Note that, in order to free an event loop object,
all remaining event sources of the event loop also need to be
freed as each keeps a reference to it.</para>
<para><function>sd_event_unrefp()</function> is similar to
<function>sd_event_unref()</function> but takes a pointer to a
pointer to an <type>sd_event</type> object. This call is useful in
conjunction with GCC's and LLVM's <ulink
url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
Variable Attribute</ulink>. Note that this function is defined as
inline function. Use a declaration like the following,
in order to allocate an event loop object that is freed
automatically as the code block is left:</para>
<programlisting>{
__attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
int r;
…
r = sd_event_default(&event);
if (r < 0)
fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
…
}</programlisting>
<para><function>sd_event_ref()</function>,
<function>sd_event_unref()</function> and
<function>sd_event_unrefp()</function> execute no operation if the
passed in event loop object is <constant>NULL</constant>.</para>
<para><function>sd_event_get_tid()</function> retrieves the thread
identifier ("TID") of the thread the specified event loop object
is associated with. This call is only supported for event loops
allocated with <function>sd_event_default()</function>, and
returns the identifier for the thread the event loop is the
default event loop of. See <citerefentry
project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for more information on thread identifiers.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success, <function>sd_event_new()</function>,
<function>sd_event_default()</function> and
<function>sd_event_get_tid()</function> return 0 or a positive
integer. On failure, they return a negative errno-style error
code. <function>sd_event_ref()</function> always returns a pointer
to the event loop object passed
in. <function>sd_event_unref()</function> always returns
<constant>NULL</constant>.</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 the object.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-EMFILE</constant></term>
<listitem><para>The maximum number of event loops has been allocated.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>-ENXIO</constant></term>
<listitem><para><function>sd_event_get_tid()</function> was
invoked on an event loop object that was not allocated with
<function>sd_event_default()</function>.</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_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_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_add_post</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_add_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_event_run</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>gettid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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