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

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

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

  <refentryinfo>
    <title>sd_event_add_child</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_child</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_event_add_child</refname>
    <refname>sd_event_source_get_child_pid</refname>
    <refname>sd_event_child_handler_t</refname>

    <refpurpose>Add a child process state change 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_child_handler_t</function>)</funcdef>
        <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
        <paramdef>const siginfo_t *<parameter>si</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_add_child</function></funcdef>
        <paramdef>sd_event *<parameter>event</parameter></paramdef>
        <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
        <paramdef>pid_t <parameter>pid</parameter></paramdef>
        <paramdef>int <parameter>options</parameter></paramdef>
        <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>
        <paramdef>void *<parameter>userdata</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>
        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
        <paramdef>pid_t *<parameter>pid</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_event_add_child()</function> adds a new child
    process state change event source to an event loop. The event loop
    object is specified in the <parameter>event</parameter> parameter,
    the event source object is returned in the
    <parameter>source</parameter> parameter. The
    <parameter>pid</parameter> parameter specifies the PID of the
    process to watch. The <parameter>handler</parameter> must
    reference a function to call when the process changes state. 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>siginfo_t</structname> structure containing
    information about the child process event. The
    <parameter>options</parameter> parameter determines which state
    changes will be watched for. It must contain an OR-ed mask of
    <constant>WEXITED</constant> (watch for the child process
    terminating), <constant>WSTOPPED</constant> (watch for the child
    process being stopped by a signal), and
    <constant>WCONTINUED</constant> (watch for the child process being
    resumed by a signal). See <citerefentry
    project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    for further information.</para>

    <para>Only a single handler may be installed for a specific
    child process. The handler is enabled for a single event
    (<constant>SD_EVENT_ONESHOT</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 when there's still a
    reference to it kept, consider setting the event source to
    <constant>SD_EVENT_OFF</constant> with
    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

    <para>If the second parameter of
    <function>sd_event_add_child()</function> is passed as NULL 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>Note that the <parameter>handler</parameter> function is
    invoked at a time where the child process is not reaped yet (and
    thus still is exposed as a zombie process by the kernel). However,
    the child will be reaped automatically after the function
    returns. Child processes for which no child process state change
    event sources are installed will not be reaped by the event loop
    implementation.</para>

    <para>If both a child process state change event source and a
    <constant>SIGCHLD</constant> signal event source is installed in
    the same event loop, the configured event source priorities decide
    which event source is dispatched first. If the signal handler is
    processed first, it should leave the child processes for which
    child process state change event sources are installed unreaped.</para>

    <para><function>sd_event_source_get_child_pid()</function>
    retrieves the configured PID of a child process state change event
    source created previously with
    <function>sd_event_add_child()</function>. It takes the event
    source object as the <parameter>source</parameter> parameter and a
    pointer to a <type>pid_t</type> variable to return the process ID
    in.
    </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. This includes
        specifying an empty mask in <parameter>options</parameter> or a mask
        which contains values different than a combination of
        <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
        <constant>WCONTINUED</constant>.
        </para></listitem>

      </varlistentry>

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

        <listitem><para>A handler is already installed for this
        child process.</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 child process 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_signal</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_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
Commit	Line	Data
3802a3d3	1	<?xml version='1.0'?> <!--- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil --->
edf25737	2	<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
12b42c76	3	"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
edf25737 ZJS	4
edf25737 ZJS	5	<!--
572eb058 ZJS	6	SPDX-License-Identifier: LGPL-2.1+
572eb058 ZJS	7
5de0ccff	8	This file is part of systemd.
edf25737	9
5de0ccff	10	Copyright 2014 Zbigniew Jędrzejewski-Szmek
edf25737 ZJS	11	-->
edf25737 ZJS	12
dc83f27a	13	<refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude">
edf25737 ZJS	14
	15	<refentryinfo>
	16	<title>sd_event_add_child</title>
	17	<productname>systemd</productname>
	18
	19	<authorgroup>
	20	<author>
	21	<contrib>More text</contrib>
	22	<firstname>Zbigniew</firstname>
	23	<surname>Jędrzejewski-Szmek</surname>
	24	<email>zbyszek@in.waw.pl</email>
	25	</author>
	26	</authorgroup>
	27	</refentryinfo>
	28
	29	<refmeta>
	30	<refentrytitle>sd_event_add_child</refentrytitle>
	31	<manvolnum>3</manvolnum>
	32	</refmeta>
	33
	34	<refnamediv>
	35	<refname>sd_event_add_child</refname>
	36	<refname>sd_event_source_get_child_pid</refname>
dc83f27a	37	<refname>sd_event_child_handler_t</refname>
edf25737	38
dc83f27a	39	<refpurpose>Add a child process state change event source to an event loop</refpurpose>
edf25737 ZJS	40	</refnamediv>
	41
	42	<refsynopsisdiv>
	43	<funcsynopsis>
dc83f27a LP	44	<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
	45
	46	<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
	47
	48	<funcprototype>
	49	<funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef>
	50	<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
	51	<paramdef>const siginfo_t *<parameter>si</parameter></paramdef>
	52	<paramdef>void *<parameter>userdata</parameter></paramdef>
	53	</funcprototype>
edf25737 ZJS	54
	55	<funcprototype>
	56	<funcdef>int <function>sd_event_add_child</function></funcdef>
	57	<paramdef>sd_event *<parameter>event</parameter></paramdef>
	58	<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
	59	<paramdef>pid_t <parameter>pid</parameter></paramdef>
	60	<paramdef>int <parameter>options</parameter></paramdef>
	61	<paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>
	62	<paramdef>void *<parameter>userdata</parameter></paramdef>
	63	</funcprototype>
	64
edf25737 ZJS	65	<funcprototype>
	66	<funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>
	67	<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
	68	<paramdef>pid_t *<parameter>pid</parameter></paramdef>
	69	</funcprototype>
	70
	71	</funcsynopsis>
	72	</refsynopsisdiv>
	73
	74	<refsect1>
	75	<title>Description</title>
	76
	77	<para><function>sd_event_add_child()</function> adds a new child
dc83f27a LP	78	process state change event source to an event loop. The event loop
	79	object is specified in the <parameter>event</parameter> parameter,
	80	the event source object is returned in the
	81	<parameter>source</parameter> parameter. The
	82	<parameter>pid</parameter> parameter specifies the PID of the
	83	process to watch. The <parameter>handler</parameter> must
	84	reference a function to call when the process changes state. The
	85	handler function will be passed the
	86	<parameter>userdata</parameter> pointer, which may be chosen
	87	freely by the caller. The handler also receives a pointer to a
	88	<structname>siginfo_t</structname> structure containing
	89	information about the child process event. The
	90	<parameter>options</parameter> parameter determines which state
	91	changes will be watched for. It must contain an OR-ed mask of
	92	<constant>WEXITED</constant> (watch for the child process
edf25737	93	terminating), <constant>WSTOPPED</constant> (watch for the child
dc83f27a LP	94	process being stopped by a signal), and
	95	<constant>WCONTINUED</constant> (watch for the child process being
	96	resumed by a signal). See <citerefentry
	97	project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
922d948b	98	for further information.</para>
edf25737 ZJS	99
edf25737 ZJS	100	<para>Only a single handler may be installed for a specific
dc83f27a LP	101	child process. The handler is enabled for a single event
	102	(<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
	103	with
edf25737 ZJS	104	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
edf25737 ZJS	105	If the handler function returns a negative error code, it will be
dc83f27a LP	106	disabled after the invocation, even if the
dc83f27a LP	107	<constant>SD_EVENT_ON</constant> mode was requested before.
edf25737 ZJS	108	</para>
edf25737 ZJS	109
dc83f27a LP	110	<para>To destroy an event source object use
	111	<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	112	but note that the event source is only removed from the event loop
	113	when all references to the event source are dropped. To make sure
	114	an event source does not fire anymore, even when there's still a
	115	reference to it kept, consider setting the event source to
	116	<constant>SD_EVENT_OFF</constant> with
	117	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
	118
7f3fdb7f	119	<para>If the second parameter of
dc83f27a LP	120	<function>sd_event_add_child()</function> is passed as NULL no
	121	reference to the event source object is returned. In this case the
	122	event source is considered "floating", and will be destroyed
	123	implicitly when the event loop itself is destroyed.</para>
	124
	125	<para>Note that the <parameter>handler</parameter> function is
	126	invoked at a time where the child process is not reaped yet (and
	127	thus still is exposed as a zombie process by the kernel). However,
	128	the child will be reaped automatically after the function
	129	returns. Child processes for which no child process state change
	130	event sources are installed will not be reaped by the event loop
	131	implementation.</para>
	132
	133	<para>If both a child process state change event source and a
	134	<constant>SIGCHLD</constant> signal event source is installed in
	135	the same event loop, the configured event source priorities decide
	136	which event source is dispatched first. If the signal handler is
	137	processed first, it should leave the child processes for which
	138	child process state change event sources are installed unreaped.</para>
	139
edf25737	140	<para><function>sd_event_source_get_child_pid()</function>
dc83f27a LP	141	retrieves the configured PID of a child process state change event
dc83f27a LP	142	source created previously with
edf25737 ZJS	143	<function>sd_event_add_child()</function>. It takes the event
edf25737 ZJS	144	source object as the <parameter>source</parameter> parameter and a
dc83f27a LP	145	pointer to a <type>pid_t</type> variable to return the process ID
dc83f27a LP	146	in.
edf25737 ZJS	147	</para>
	148	</refsect1>
	149
	150	<refsect1>
	151	<title>Return Value</title>
	152
	153	<para>On success, these functions return 0 or a positive
	154	integer. On failure, they return a negative errno-style error
	155	code.</para>
	156	</refsect1>
	157
	158	<refsect1>
	159	<title>Errors</title>
	160
	161	<para>Returned errors may indicate the following problems:</para>
	162
	163	<variablelist>
	164	<varlistentry>
8474b70c	165	<term><constant>-ENOMEM</constant></term>
edf25737 ZJS	166
	167	<listitem><para>Not enough memory to allocate an object.</para></listitem>
	168	</varlistentry>
	169
	170	<varlistentry>
8474b70c	171	<term><constant>-EINVAL</constant></term>
edf25737 ZJS	172
edf25737 ZJS	173	<listitem><para>An invalid argument has been passed. This includes
cc98b302	174	specifying an empty mask in <parameter>options</parameter> or a mask
f131770b	175	which contains values different than a combination of
edf25737 ZJS	176	<constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
	177	<constant>WCONTINUED</constant>.
	178	</para></listitem>
	179
	180	</varlistentry>
	181
	182	<varlistentry>
8474b70c	183	<term><constant>-EBUSY</constant></term>
edf25737	184
a8eaaee7	185	<listitem><para>A handler is already installed for this
dc83f27a	186	child process.</para></listitem>
edf25737 ZJS	187
	188	</varlistentry>
	189
	190	<varlistentry>
8474b70c	191	<term><constant>-ESTALE</constant></term>
edf25737 ZJS	192
	193	<listitem><para>The event loop is already terminated.</para></listitem>
	194
	195	</varlistentry>
	196
	197	<varlistentry>
8474b70c	198	<term><constant>-ECHILD</constant></term>
edf25737 ZJS	199
	200	<listitem><para>The event loop has been created in a different process.</para></listitem>
	201
	202	</varlistentry>
	203
dc83f27a LP	204	<varlistentry>
dc83f27a LP	205	<term><constant>-EDOM</constant></term>
edf25737	206
dc83f27a LP	207	<listitem><para>The passed event source is not a child process event source.</para></listitem>
dc83f27a LP	208	</varlistentry>
edf25737	209
dc83f27a	210	</variablelist>
edf25737 ZJS	211	</refsect1>
edf25737 ZJS	212
dc83f27a LP	213	<xi:include href="libsystemd-pkgconfig.xml" />
dc83f27a LP	214
edf25737 ZJS	215	<refsect1>
	216	<title>See Also</title>
	217
	218	<para>
	219	<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
	220	<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	221	<citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
dc83f27a LP	222	<citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
dc83f27a LP	223	<citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
edf25737 ZJS	224	<citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
edf25737 ZJS	225	<citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
4dfefc19	226	<citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
dc83f27a LP	227	<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	228	<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	229	<citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	230	<citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
	231	<citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
edf25737 ZJS	232	</para>
	233	</refsect1>
	234
	235	</refentry>