man/sd_event_add_child.xml

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   8   Copyright 2014 Zbigniew Jędrzejewski-Szmek
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  23
  24 <refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude">
  25
  26   <refentryinfo>
  27     <title>sd_event_add_child</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>More text</contrib>
  33         <firstname>Zbigniew</firstname>
  34         <surname>Jędrzejewski-Szmek</surname>
  35         <email>zbyszek@in.waw.pl</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_event_add_child</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_event_add_child</refname>
  47     <refname>sd_event_source_get_child_pid</refname>
  48     <refname>sd_event_child_handler_t</refname>
  49
  50     <refpurpose>Add a child process state change event source to an event loop</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <funcsynopsis>
  55       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  56
  57       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  58
  59       <funcprototype>
  60         <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef>
  61         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  62         <paramdef>const siginfo_t *<parameter>si</parameter></paramdef>
  63         <paramdef>void *<parameter>userdata</parameter></paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_event_add_child</function></funcdef>
  68         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  69         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  70         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  71         <paramdef>int <parameter>options</parameter></paramdef>
  72         <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef>
  73         <paramdef>void *<parameter>userdata</parameter></paramdef>
  74       </funcprototype>
  75
  76       <funcprototype>
  77         <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef>
  78         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  79         <paramdef>pid_t *<parameter>pid</parameter></paramdef>
  80       </funcprototype>
  81
  82     </funcsynopsis>
  83   </refsynopsisdiv>
  84
  85   <refsect1>
  86     <title>Description</title>
  87
  88     <para><function>sd_event_add_child()</function> adds a new child
  89     process state change event source to an event loop. The event loop
  90     object is specified in the <parameter>event</parameter> parameter,
  91     the event source object is returned in the
  92     <parameter>source</parameter> parameter. The
  93     <parameter>pid</parameter> parameter specifies the PID of the
  94     process to watch. The <parameter>handler</parameter> must
  95     reference a function to call when the process changes state. The
  96     handler function will be passed the
  97     <parameter>userdata</parameter> pointer, which may be chosen
  98     freely by the caller. The handler also receives a pointer to a
  99     <structname>siginfo_t</structname> structure containing
 100     information about the child process event. The
 101     <parameter>options</parameter> parameter determines which state
 102     changes will be watched for. It must contain an OR-ed mask of
 103     <constant>WEXITED</constant> (watch for the child process
 104     terminating), <constant>WSTOPPED</constant> (watch for the child
 105     process being stopped by a signal), and
 106     <constant>WCONTINUED</constant> (watch for the child process being
 107     resumed by a signal). See <citerefentry
 108     project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 109     for further information.</para>
 110
 111     <para>Only a single handler may be installed for a specific
 112     child process. The handler is enabled for a single event
 113     (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed
 114     with
 115     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 116     If the handler function returns a negative error code, it will be
 117     disabled after the invocation, even if the
 118     <constant>SD_EVENT_ON</constant> mode was requested before.
 119     </para>
 120
 121     <para>To destroy an event source object use
 122     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 123     but note that the event source is only removed from the event loop
 124     when all references to the event source are dropped. To make sure
 125     an event source does not fire anymore, even when there's still a
 126     reference to it kept, consider setting the event source to
 127     <constant>SD_EVENT_OFF</constant> with
 128     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 129
 130     <para>If the second parameter of
 131     <function>sd_event_add_child()</function> is passed as NULL no
 132     reference to the event source object is returned. In this case the
 133     event source is considered "floating", and will be destroyed
 134     implicitly when the event loop itself is destroyed.</para>
 135
 136     <para>Note that the <parameter>handler</parameter> function is
 137     invoked at a time where the child process is not reaped yet (and
 138     thus still is exposed as a zombie process by the kernel). However,
 139     the child will be reaped automatically after the function
 140     returns. Child processes for which no child process state change
 141     event sources are installed will not be reaped by the event loop
 142     implementation.</para>
 143
 144     <para>If both a child process state change event source and a
 145     <constant>SIGCHLD</constant> signal event source is installed in
 146     the same event loop, the configured event source priorities decide
 147     which event source is dispatched first. If the signal handler is
 148     processed first, it should leave the child processes for which
 149     child process state change event sources are installed unreaped.</para>
 150
 151     <para><function>sd_event_source_get_child_pid()</function>
 152     retrieves the configured PID of a child process state change event
 153     source created previously with
 154     <function>sd_event_add_child()</function>. It takes the event
 155     source object as the <parameter>source</parameter> parameter and a
 156     pointer to a <type>pid_t</type> variable to return the process ID
 157     in.
 158     </para>
 159   </refsect1>
 160
 161   <refsect1>
 162     <title>Return Value</title>
 163
 164     <para>On success, these functions return 0 or a positive
 165     integer. On failure, they return a negative errno-style error
 166     code.</para>
 167   </refsect1>
 168
 169   <refsect1>
 170     <title>Errors</title>
 171
 172     <para>Returned errors may indicate the following problems:</para>
 173
 174     <variablelist>
 175       <varlistentry>
 176         <term><constant>-ENOMEM</constant></term>
 177
 178         <listitem><para>Not enough memory to allocate an object.</para></listitem>
 179       </varlistentry>
 180
 181       <varlistentry>
 182         <term><constant>-EINVAL</constant></term>
 183
 184         <listitem><para>An invalid argument has been passed. This includes
 185         specifying an empty mask in <parameter>options</parameter> or a mask
 186         which contains values different than a combination of
 187         <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and
 188         <constant>WCONTINUED</constant>.
 189         </para></listitem>
 190
 191       </varlistentry>
 192
 193       <varlistentry>
 194         <term><constant>-EBUSY</constant></term>
 195
 196         <listitem><para>A handler is already installed for this
 197         child process.</para></listitem>
 198
 199       </varlistentry>
 200
 201       <varlistentry>
 202         <term><constant>-ESTALE</constant></term>
 203
 204         <listitem><para>The event loop is already terminated.</para></listitem>
 205
 206       </varlistentry>
 207
 208       <varlistentry>
 209         <term><constant>-ECHILD</constant></term>
 210
 211         <listitem><para>The event loop has been created in a different process.</para></listitem>
 212
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><constant>-EDOM</constant></term>
 217
 218         <listitem><para>The passed event source is not a child process event source.</para></listitem>
 219       </varlistentry>
 220
 221     </variablelist>
 222   </refsect1>
 223
 224   <xi:include href="libsystemd-pkgconfig.xml" />
 225
 226   <refsect1>
 227     <title>See Also</title>
 228
 229     <para>
 230       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 231       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 232       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 233       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 234       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 235       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 236       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 237       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 238       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 239       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 240       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 241       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 242       <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 243     </para>
 244   </refsect1>
 245
 246 </refentry>