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

<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>