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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd_event_new" xmlns:xi="http://www.w3.org/2001/XInclude">

<refentryinfo>

<title>sd_event_new</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>Developer</contrib>

<firstname>Lennart</firstname>

<surname>Poettering</surname>

<email>lennart@poettering.net</email>

</author>

</authorgroup>

</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 &lt;systemd/sd-event.h&gt;</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(&amp;event);

if (r &lt; 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> and

<function>sd_event_default()</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>