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