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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"> |
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4 | |
5 | <!-- | |
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6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
96b2fb93 | 8 | Copyright © 2014 Zbigniew Jędrzejewski-Szmek |
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9 | --> |
10 | ||
dc83f27a | 11 | <refentry id="sd_event_add_child" xmlns:xi="http://www.w3.org/2001/XInclude"> |
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12 | |
13 | <refentryinfo> | |
14 | <title>sd_event_add_child</title> | |
15 | <productname>systemd</productname> | |
16 | ||
17 | <authorgroup> | |
18 | <author> | |
19 | <contrib>More text</contrib> | |
20 | <firstname>Zbigniew</firstname> | |
21 | <surname>Jędrzejewski-Szmek</surname> | |
22 | <email>zbyszek@in.waw.pl</email> | |
23 | </author> | |
24 | </authorgroup> | |
25 | </refentryinfo> | |
26 | ||
27 | <refmeta> | |
28 | <refentrytitle>sd_event_add_child</refentrytitle> | |
29 | <manvolnum>3</manvolnum> | |
30 | </refmeta> | |
31 | ||
32 | <refnamediv> | |
33 | <refname>sd_event_add_child</refname> | |
34 | <refname>sd_event_source_get_child_pid</refname> | |
dc83f27a | 35 | <refname>sd_event_child_handler_t</refname> |
edf25737 | 36 | |
dc83f27a | 37 | <refpurpose>Add a child process state change event source to an event loop</refpurpose> |
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38 | </refnamediv> |
39 | ||
40 | <refsynopsisdiv> | |
41 | <funcsynopsis> | |
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42 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> |
43 | ||
44 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
45 | ||
46 | <funcprototype> | |
47 | <funcdef>typedef int (*<function>sd_event_child_handler_t</function>)</funcdef> | |
48 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
49 | <paramdef>const siginfo_t *<parameter>si</parameter></paramdef> | |
50 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
51 | </funcprototype> | |
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52 | |
53 | <funcprototype> | |
54 | <funcdef>int <function>sd_event_add_child</function></funcdef> | |
55 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
56 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
57 | <paramdef>pid_t <parameter>pid</parameter></paramdef> | |
58 | <paramdef>int <parameter>options</parameter></paramdef> | |
59 | <paramdef>sd_event_child_handler_t <parameter>handler</parameter></paramdef> | |
60 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
61 | </funcprototype> | |
62 | ||
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63 | <funcprototype> |
64 | <funcdef>int <function>sd_event_source_get_child_pid</function></funcdef> | |
65 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
66 | <paramdef>pid_t *<parameter>pid</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | </funcsynopsis> | |
70 | </refsynopsisdiv> | |
71 | ||
72 | <refsect1> | |
73 | <title>Description</title> | |
74 | ||
75 | <para><function>sd_event_add_child()</function> adds a new child | |
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76 | process state change event source to an event loop. The event loop |
77 | object is specified in the <parameter>event</parameter> parameter, | |
78 | the event source object is returned in the | |
79 | <parameter>source</parameter> parameter. The | |
80 | <parameter>pid</parameter> parameter specifies the PID of the | |
81 | process to watch. The <parameter>handler</parameter> must | |
82 | reference a function to call when the process changes state. The | |
83 | handler function will be passed the | |
84 | <parameter>userdata</parameter> pointer, which may be chosen | |
85 | freely by the caller. The handler also receives a pointer to a | |
86 | <structname>siginfo_t</structname> structure containing | |
87 | information about the child process event. The | |
88 | <parameter>options</parameter> parameter determines which state | |
89 | changes will be watched for. It must contain an OR-ed mask of | |
90 | <constant>WEXITED</constant> (watch for the child process | |
edf25737 | 91 | terminating), <constant>WSTOPPED</constant> (watch for the child |
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92 | process being stopped by a signal), and |
93 | <constant>WCONTINUED</constant> (watch for the child process being | |
94 | resumed by a signal). See <citerefentry | |
95 | project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
922d948b | 96 | for further information.</para> |
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97 | |
98 | <para>Only a single handler may be installed for a specific | |
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99 | child process. The handler is enabled for a single event |
100 | (<constant>SD_EVENT_ONESHOT</constant>), but this may be changed | |
101 | with | |
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102 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
103 | If the handler function returns a negative error code, it will be | |
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104 | disabled after the invocation, even if the |
105 | <constant>SD_EVENT_ON</constant> mode was requested before. | |
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106 | </para> |
107 | ||
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108 | <para>To destroy an event source object use |
109 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
110 | but note that the event source is only removed from the event loop | |
111 | when all references to the event source are dropped. To make sure | |
112 | an event source does not fire anymore, even when there's still a | |
113 | reference to it kept, consider setting the event source to | |
114 | <constant>SD_EVENT_OFF</constant> with | |
115 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
116 | ||
7f3fdb7f | 117 | <para>If the second parameter of |
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118 | <function>sd_event_add_child()</function> is passed as NULL no |
119 | reference to the event source object is returned. In this case the | |
120 | event source is considered "floating", and will be destroyed | |
121 | implicitly when the event loop itself is destroyed.</para> | |
122 | ||
123 | <para>Note that the <parameter>handler</parameter> function is | |
124 | invoked at a time where the child process is not reaped yet (and | |
125 | thus still is exposed as a zombie process by the kernel). However, | |
126 | the child will be reaped automatically after the function | |
127 | returns. Child processes for which no child process state change | |
128 | event sources are installed will not be reaped by the event loop | |
129 | implementation.</para> | |
130 | ||
131 | <para>If both a child process state change event source and a | |
132 | <constant>SIGCHLD</constant> signal event source is installed in | |
133 | the same event loop, the configured event source priorities decide | |
134 | which event source is dispatched first. If the signal handler is | |
135 | processed first, it should leave the child processes for which | |
136 | child process state change event sources are installed unreaped.</para> | |
137 | ||
edf25737 | 138 | <para><function>sd_event_source_get_child_pid()</function> |
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139 | retrieves the configured PID of a child process state change event |
140 | source created previously with | |
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141 | <function>sd_event_add_child()</function>. It takes the event |
142 | source object as the <parameter>source</parameter> parameter and a | |
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143 | pointer to a <type>pid_t</type> variable to return the process ID |
144 | in. | |
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145 | </para> |
146 | </refsect1> | |
147 | ||
148 | <refsect1> | |
149 | <title>Return Value</title> | |
150 | ||
151 | <para>On success, these functions return 0 or a positive | |
152 | integer. On failure, they return a negative errno-style error | |
153 | code.</para> | |
154 | </refsect1> | |
155 | ||
156 | <refsect1> | |
157 | <title>Errors</title> | |
158 | ||
159 | <para>Returned errors may indicate the following problems:</para> | |
160 | ||
161 | <variablelist> | |
162 | <varlistentry> | |
8474b70c | 163 | <term><constant>-ENOMEM</constant></term> |
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164 | |
165 | <listitem><para>Not enough memory to allocate an object.</para></listitem> | |
166 | </varlistentry> | |
167 | ||
168 | <varlistentry> | |
8474b70c | 169 | <term><constant>-EINVAL</constant></term> |
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170 | |
171 | <listitem><para>An invalid argument has been passed. This includes | |
cc98b302 | 172 | specifying an empty mask in <parameter>options</parameter> or a mask |
f131770b | 173 | which contains values different than a combination of |
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174 | <constant>WEXITED</constant>, <constant>WSTOPPED</constant>, and |
175 | <constant>WCONTINUED</constant>. | |
176 | </para></listitem> | |
177 | ||
178 | </varlistentry> | |
179 | ||
180 | <varlistentry> | |
8474b70c | 181 | <term><constant>-EBUSY</constant></term> |
edf25737 | 182 | |
a8eaaee7 | 183 | <listitem><para>A handler is already installed for this |
dc83f27a | 184 | child process.</para></listitem> |
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185 | |
186 | </varlistentry> | |
187 | ||
188 | <varlistentry> | |
8474b70c | 189 | <term><constant>-ESTALE</constant></term> |
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190 | |
191 | <listitem><para>The event loop is already terminated.</para></listitem> | |
192 | ||
193 | </varlistentry> | |
194 | ||
195 | <varlistentry> | |
8474b70c | 196 | <term><constant>-ECHILD</constant></term> |
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197 | |
198 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
199 | ||
200 | </varlistentry> | |
201 | ||
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202 | <varlistentry> |
203 | <term><constant>-EDOM</constant></term> | |
edf25737 | 204 | |
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205 | <listitem><para>The passed event source is not a child process event source.</para></listitem> |
206 | </varlistentry> | |
edf25737 | 207 | |
dc83f27a | 208 | </variablelist> |
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209 | </refsect1> |
210 | ||
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211 | <xi:include href="libsystemd-pkgconfig.xml" /> |
212 | ||
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213 | <refsect1> |
214 | <title>See Also</title> | |
215 | ||
216 | <para> | |
217 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
218 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
219 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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220 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
221 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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222 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
223 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 224 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
4dfefc19 | 225 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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226 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
227 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
228 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
229 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
230 | <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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231 | </para> |
232 | </refsect1> | |
233 | ||
234 | </refentry> |