[thirdparty/systemd.git] / man / sd_event_add_signal.xml

<?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+

  Copyright © 2014 Zbigniew Jędrzejewski-Szmek
-->

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

  <refentryinfo>
    <title>sd_event_add_signal</title>
    <productname>systemd</productname>
  </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_inotify</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>
Commit	Line	Data
	1	<?xml version='1.0'?> <!--- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil --->
	2	<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
	3	"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
	4
	5	<!--
	6	SPDX-License-Identifier: LGPL-2.1+
	7
	8	Copyright © 2014 Zbigniew Jędrzejewski-Szmek
	9	-->
	10
	11	<refentry id="sd_event_add_signal" xmlns:xi="http://www.w3.org/2001/XInclude">
	12
	13	<refentryinfo>
	14	<title>sd_event_add_signal</title>
	15	<productname>systemd</productname>
	16	</refentryinfo>
	17
	18	<refmeta>
	19	<refentrytitle>sd_event_add_signal</refentrytitle>
	20	<manvolnum>3</manvolnum>
	21	</refmeta>
	22
	23	<refnamediv>
	24	<refname>sd_event_add_signal</refname>
	25	<refname>sd_event_source_get_signal</refname>
	26	<refname>sd_event_signal_handler_t</refname>
	27
	28	<refpurpose>Add a UNIX process signal event source to an event
	29	loop</refpurpose>
	30	</refnamediv>
	31
	32	<refsynopsisdiv>
	33	<funcsynopsis>
	34	<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
	35
	36	<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
	37
	38	<funcprototype>
	39	<funcdef>typedef int (*<function>sd_event_signal_handler_t</function>)</funcdef>
	40	<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
	41	<paramdef>const struct signalfd_siginfo *<parameter>si</parameter></paramdef>
	42	<paramdef>void *<parameter>userdata</parameter></paramdef>
	43	</funcprototype>
	44
	45	<funcprototype>
	46	<funcdef>int <function>sd_event_add_signal</function></funcdef>
	47	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	48	<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
	49	<paramdef>int <parameter>signal</parameter></paramdef>
	50	<paramdef>sd_event_signal_handler_t <parameter>handler</parameter></paramdef>
	51	<paramdef>void *<parameter>userdata</parameter></paramdef>
	52	</funcprototype>
	53
	54	<funcprototype>
	55	<funcdef>int <function>sd_event_source_get_signal</function></funcdef>
	56	<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
	57	</funcprototype>
	58
	59	</funcsynopsis>
	60	</refsynopsisdiv>
	61
	62	<refsect1>
	63	<title>Description</title>
	64
	65	<para><function>sd_event_add_signal()</function> adds a new UNIX
	66	process signal event source to an event loop. The event loop
	67	object is specified in the <parameter>event</parameter> parameter,
	68	and the event source object is returned in the
	69	<parameter>source</parameter> parameter. The
	70	<parameter>signal</parameter> parameter specifies the numeric
	71	signal to be handled (see <citerefentry
	72	project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
	73	The <parameter>handler</parameter> parameter must reference a
	74	function to call when the signal is received or be
	75	<constant>NULL</constant>. The handler function will be passed
	76	the <parameter>userdata</parameter> pointer, which may be chosen
	77	freely by the caller. The handler also receives a pointer to a
	78	<structname>signalfd_siginfo</structname> structure containing
	79	information about the received signal. See <citerefentry
	80	project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
	81	for further information.</para>
	82
	83	<para>Only a single handler may be installed for a specific
	84	signal. The signal will be unblocked by this call, and must be
	85	blocked before this function is called in all threads (using
	86	<citerefentry
	87	project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>). If
	88	the handler is not specified (<parameter>handler</parameter> is
	89	<constant>NULL</constant>), a default handler which causes the
	90	program to exit cleanly will be used.</para>
	91
	92	<para>By default, the event source is enabled permanently
	93	(<constant>SD_EVENT_ON</constant>), but this may be changed with
	94	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
	95	If the handler function returns a negative error code, it will be
	96	disabled after the invocation, even if the
	97	<constant>SD_EVENT_ON</constant> mode was requested before.
	98	</para>
	99
	100	<para>To destroy an event source object use
	101	<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	102	but note that the event source is only removed from the event loop
	103	when all references to the event source are dropped. To make sure
	104	an event source does not fire anymore, even if it is still referenced,
	105	disable the event source using
	106	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
	107	with <constant>SD_EVENT_OFF</constant>.</para>
	108
	109	<para>If the second parameter of
	110	<function>sd_event_add_signal()</function> is
	111	<constant>NULL</constant> no reference to the event source object
	112	is returned. In this case the event source is considered
	113	"floating", and will be destroyed implicitly when the event loop
	114	itself is destroyed.</para>
	115
	116	<para><function>sd_event_source_get_signal()</function> returns
	117	the configured signal number of an event source created previously
	118	with <function>sd_event_add_signal()</function>. It takes the
	119	event source object as the <parameter>source</parameter>
	120	parameter.</para>
	121	</refsect1>
	122
	123	<refsect1>
	124	<title>Return Value</title>
	125
	126	<para>On success, these functions return 0 or a positive
	127	integer. On failure, they return a negative errno-style error
	128	code.</para>
	129	</refsect1>
	130
	131	<refsect1>
	132	<title>Errors</title>
	133
	134	<para>Returned errors may indicate the following problems:</para>
	135
	136	<variablelist>
	137	<varlistentry>
	138	<term><constant>-ENOMEM</constant></term>
	139
	140	<listitem><para>Not enough memory to allocate an object.</para></listitem>
	141	</varlistentry>
	142
	143	<varlistentry>
	144	<term><constant>-EINVAL</constant></term>
	145
	146	<listitem><para>An invalid argument has been passed.</para></listitem>
	147	</varlistentry>
	148
	149	<varlistentry>
	150	<term><constant>-EBUSY</constant></term>
	151
	152	<listitem><para>A handler is already installed for this
	153	signal or the signal was not blocked previously.</para></listitem>
	154	</varlistentry>
	155
	156	<varlistentry>
	157	<term><constant>-ESTALE</constant></term>
	158
	159	<listitem><para>The event loop is already terminated.</para></listitem>
	160	</varlistentry>
	161
	162	<varlistentry>
	163	<term><constant>-ECHILD</constant></term>
	164
	165	<listitem><para>The event loop has been created in a different process.</para></listitem>
	166	</varlistentry>
	167
	168	<varlistentry>
	169	<term><constant>-EDOM</constant></term>
	170
	171	<listitem><para>The passed event source is not a signal event source.</para></listitem>
	172	</varlistentry>
	173
	174	</variablelist>
	175	</refsect1>
	176
	177	<xi:include href="libsystemd-pkgconfig.xml" />
	178
	179	<refsect1>
	180	<title>See Also</title>
	181
	182	<para>
	183	<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
	184	<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	185	<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	186	<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	187	<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	188	<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	189	<citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	190	<citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	191	<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	192	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	193	<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	194	<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	195	<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
	196	<citerefentry project='man-pages'><refentrytitle>signalfd</refentrytitle><manvolnum>2</manvolnum></citerefentry>
	197	</para>
	198	</refsect1>
	199
	200	</refentry>