<?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"> <!-- This file is part of systemd. Copyright 2014 Zbigniew Jędrzejewski-Szmek systemd is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. systemd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with systemd; If not, see <http://www.gnu.org/licenses/>. --> <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 <systemd/sd-event.h></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>