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

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

<refentryinfo>

<title>sd_event_add_signal</title>

<productname>systemd</productname>

<authorgroup>

<author>

<contrib>More text</contrib>

<firstname>Zbigniew</firstname>

<surname>Jędrzejewski-Szmek</surname>

<email>zbyszek@in.waw.pl</email>

</author>

</authorgroup>

</refentryinfo>

<refmeta>

<refentrytitle>sd_event_add_signal</refentrytitle>

<manvolnum>3</manvolnum>

</refmeta>

<refnamediv>

<refname>sd_event_add_signal</refname>

<refname>sd_event_source_get_signal</refname>

<refname>sd_event_signal_handler_t</refname>

<refpurpose>Add a UNIX process signal event source to an event

loop</refpurpose>

</refnamediv>

<refsynopsisdiv>

<funcsynopsis>

<funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>

<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>

<funcprototype>

<funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>

<paramdef>sd_event_source *<parameter>s</parameter></paramdef>

<paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>

<paramdef>void *<parameter>userdata</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>int <function>sd_event_add_signal</function></funcdef>

<paramdef>sd_event *<parameter>event</parameter></paramdef>

<paramdef>sd_event_source **<parameter>source</parameter></paramdef>

<paramdef>int <parameter>signal</parameter></paramdef>

<paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>

<paramdef>void *<parameter>userdata</parameter></paramdef>

</funcprototype>

<funcprototype>

<funcdef>int <function>sd_event_source_get_signal</function></funcdef>

<paramdef>sd_event_source *<parameter>source</parameter></paramdef>

</funcprototype>

</funcsynopsis>

</refsynopsisdiv>

<refsect1>

<title>Description</title>

<para><function>sd_event_add_signal()</function> adds a new UNIX

process signal event source to an event loop. The event loop

object is specified in the <parameter>event</parameter> parameter,

and the event source object is returned in the

<parameter>source</parameter> parameter. The

<parameter>signal</parameter> parameter specifies the numeric

signal to be handled (see <citerefentry

project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).

The <parameter>handler</parameter> parameter must reference a

function to call when the signal is received or be

<constant>NULL</constant>. The handler function will be passed

the <parameter>userdata</parameter> pointer, which may be chosen

freely by the caller. The handler also receives a pointer to a

<structname>signalfd_siginfo</structname> structure containing

information about the received signal. See <citerefentry

project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>

for further information.</para>

<para>Only a single handler may be installed for a specific

signal. The signal will be unblocked by this call, and must be

blocked before this function is called in all threads (using

<citerefentry

project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If

the handler is not specified (<parameter>handler</parameter> is

<constant>NULL</constant>), a default handler which causes the

program to exit cleanly will be used.</para>

<para>By default, the event source is enabled permanently

(<constant>SD_EVENT_ON</constant>), but this may be changed with

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.

If the handler function returns a negative error code, it will be

disabled after the invocation, even if the

<constant>SD_EVENT_ON</constant> mode was requested before.

</para>

<para>To destroy an event source object use

<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

but note that the event source is only removed from the event loop

when all references to the event source are dropped. To make sure

an event source does not fire anymore, even if it is still referenced,

disable the event source using

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>

with <constant>SD_EVENT_OFF</constant>.</para>

<para>If the second parameter of

<function>sd_event_add_signal()</function> is

<constant>NULL</constant> no reference to the event source object

is returned. In this case the event source is considered

"floating", and will be destroyed implicitly when the event loop

itself is destroyed.</para>

<para><function>sd_event_source_get_signal()</function> returns

the configured signal number of an event source created previously

with <function>sd_event_add_signal()</function>. It takes the

event source object as the <parameter>source</parameter>

parameter.</para>

</refsect1>

<refsect1>

<title>Return Value</title>

<para>On success, these functions return 0 or a positive

integer. On failure, they return a negative errno-style error

code.</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 an object.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EINVAL</constant></term>

<listitem><para>An invalid argument has been passed.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EBUSY</constant></term>

<listitem><para>A handler is already installed for this

signal or the signal was not blocked previously.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ESTALE</constant></term>

<listitem><para>The event loop is already terminated.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-ECHILD</constant></term>

<listitem><para>The event loop has been created in a different process.</para></listitem>

</varlistentry>

<varlistentry>

<term><constant>-EDOM</constant></term>

<listitem><para>The passed event source is not a signal event source.</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_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_now</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_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,

<citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>